Conventional Units and SI Units in JAMA Network Journals - Units of Measure

AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020

Conventional Units and SI Units in JAMA Network Journals
Units of Measure

In the United States, most physicians and other health care professionals use conventional units for most commonly encountered clinical measurements (eg, blood pressure), and most clinical laboratories report many laboratory values by means of conventional units. To serve these readers, but also to serve the needs of readers more familiar with JAMA Network journals have adopted an approach for reporting units of measure that includes a combination of SI units and conventional units.

17.5.1 Length, Area, Volume, Mass.

Measurements of length, area, volume, and mass are reported by means of metric units rather than English units (Table 17.5-1).

Table 17.5-1. Conversions to Metric Measures

Symbol

Known quantity

Multiply by

To find

Metric symbol

Length

in

inches

2.54

centimeters

cm

ft

feet

30

centimeters

cm

ft

feet

0.3

meters

m

yd

yards

0.9

meters

m


miles

1.6

kilometers

km

Area

sq in

square inches

6.5

square centimeters

cm2

sq ft

square feet

0.09

square meters

m2

sq yd

square yards

0.8

square meters

m2


square miles

2.6

square kilometers

km2

Mass

oz

ounces

28

grams

g

lb

pounds

0.45

kilograms

kg

Volume

tsp

teaspoons

5

milliliters

mL

tbsp

tablespoons

15

milliliters

mL

fl oz

fluid ounces

30

milliliters

mL

c

cups

0.24

liters

L

pt

US pints

0.47

liters

L

qt

US quarts

0.95

liters

L

gal

US gallons

3.8

liters

L

cu ft

cubic feet

0.03

cubic meters

m3

cu yd

cubic yards

0.76

cubic meters

m3

In less formal, nonscientific texts, such as essays, use of nonmetric units, such as miles or inches, and the use of idioms, such as “An ounce of prevention is worth a pound of cure” or “give an inch,” are acceptable. In addition, if the nonmetric unit was used as part of a survey or questionnaire, the original measure should be retained.

The patients were asked, “Do you have difficulty walking 15 feet?”

Similarly, if data were measured in SI units and are displayed as such in an organized way (eg, cholesterol given in 5-mmol increments along a figure axis), the original measure may be retained, with a conversion given for the conventional unit.

17.5.2 Temperature.

The Celsius scale (°C) is used for temperature measurement rather than the base SI unit for temperature, the kelvin (K), which has little application in medicine. Although the kelvin and Celsius scales have the same interval value for temperature differences, they differ in their absolute values. For example, a temperature of 273.15 K is equal to 0 °C. Temperature values generally are reported in degrees Celsius, and values given in degrees Fahrenheit (°F) are converted to degrees Celsius (°C).

(°F − 32)(0.556) = °C

17.5.3 Time.

The SI unit for time is the second, although minute, hour, and day also are used. Other units of time, such as week, month, and year, are not part of the SI but also are used. The abbreviations for minute, hour, and day are min, h, and d, respectively, and the abbreviations for week, month, and year are wk, mo, and y, respectively. These abbreviations are used in tables, figures, and virgule constructions and are never capitalized (see 13.12, Units of Measure, and 8.4, Forward Slash [Virgule, Solidus]).

The patient reported smoking 20 cigarettes/d.

She had mild apnea, with 1 episode/h.

Respirations were 60/min; pulse rate was 98/min.

17.5.4 Visual Acuity.

Visual acuity should be reported on the basis of how the measurement was determined. For example, using the Snellen fraction with English units, 20/20 or 20/100 indicates that the person being evaluated can see at 20 ft what a person with normal visual acuity can see at 20 ft or at 100 ft, respectively. The equivalent metric measurements for visual acuity are 6/6 and 6/30, respectively (see 14.13, Nomenclature, Ophthalmology Terms).

17.5.5 Pressure.

Blood pressure and intraocular pressure are reported in millimeters of mercury (mm Hg); cerebrospinal fluid pressure is reported as centimeters of water (cm H2O). The pascal (newton per square meter [N/m2]) is the recommended SI unit for pressure but generally is not used for reporting these common physiologic pressure measurements. Partial pressure of gases (eg, of oxygen and carbon dioxide) may be reported as millimeters of mercury (mm Hg) or as kilopascals (kPa) (see 14.16, Pulmonary and Respiratory Terminology).

17.5.6 pH.

Although SI nomenclature could be used to express values of hydrogen ion concentration (nmol/L), the pH scale (1-14) is used.

17.5.7 Solutions and Concentration.

A molar solution contains 1 mol (1 g molecular weight) of solute in 1 L of solution. The SI style for reporting molar solutions is mol/L; for solutions with millimolar concentrations, mmol/L is used; and for solutions with micromolar concentrations, μmol/L is used. The concentration is given as 4-mmol/L potassium chloride not 4 mmol/L of potassium chloride.

The gel was incubated at 40 °C after applying 10 mL of a solution of 4-mmol/L potassium chloride and 5 mL of a solution of 1-mol/L sodium chloride.

Molar concentrations of solutions and reagents also may be expressed by using M to designate molar and SI prefixes to denote concentration (eg, mM for millimolar; μM for micromolar). Note that the molar concentration unit is set closed up to the number.

The gel was incubated at 40 °C after applying 10 mL of a solution of 4mM potassium chloride and 5 mL of a solution of 1M sodium chloride.

A normal solution contains a concentration of 1 gram-equivalent of solute per liter.

To show the concentration of a solution in relation to normality (N), the abbreviation N is used, with no space between the numerical value and the N (eg, 3N). Half normal is indicated as 0.5N or N/2.

17.5.8 Energy.

The calorie is the unit of measure often used in chemistry and biochemistry for reporting heat energy. A value of 1 calorie is the amount of energy (heat) required to raise the temperature of 1 g of pure water by 1 °C. The joule is the preferred SI unit for energy, and calories and kilocalories may be converted to joules (J) and kilojoules (kJ) by using the following formulas:

1 calorie = 4.186 J

1 kilocalorie = 4.186 kJ

JAMA Network journals prefer to report heat energy in calories or kilocalories.

Formerly a distinction was made between the small calorie (with a lowercase c) and the large calorie, designated as Calorie (with a capital C and abbreviated Cal)2 and equivalent to 1000 calories or 1 kilocalorie (kcal). In metabolic studies, the Calorie is the amount of heat energy required to raise or lower 1 kg of pure liquid water by 1 °C.4 The Calorie also is used in nutrition to express the energy content of food.5 By convention, the use of the capitalized C in dietary Calories indicates kilocalories (ie, 1 Cal is equivalent to 1 kcal or 1000 cal). For example, if the label on a food package indicates that a serving contains 300 Cal, that serving would yield 300 kcal (not 300 cal) of heat energy when subjected to complete combustion. JAMA Network journals prefer Calories or kilocalories for expressing the energy content of food.

Energy expenditure also is reported as Calories (or kilocalories) to reflect the amount of energy required for the work done. The values for Calorie expenditure are based on the metabolic cost, expressed as metabolic equivalents (METs). One MET represents the metabolic rate for an adult at rest (ie, set at 3.5 mL of oxygen consumed per kilogram of body mass per minute) or approximately 1 kcal/kg/h.5 Activities with MET values near 1 are sedentary activities (eg, sitting quietly), whereas activities with higher MET values involve higher levels of energy expenditure (eg, brisk walking has a MET value of 3, or 3 times the resting metabolic rate).

17.5.9 Drug Doses.

Drug doses are expressed in conventional metric mass units (eg, milligrams or milligrams per kilogram) rather than in molar SI units. Moreover, certain drugs (such as insulin or heparin) may be prepared as mixtures and have no specific molecular weight, thereby precluding their expression in mass units. Although other drug dose units, such as drops (for ophthalmologic preparations), grains (for aspirin), and various apothecary system measurements (eg, teaspoonfuls, ounces, and drams), may be encountered clinically, these units generally are not used.

Another such example is cc for mL; cc is sometimes used in clinical settings, but to avoid confusion mL should be used in scientific publications. In addition, the units for drug doses are often different from the units used to measure drug concentrations, such as in therapeutic drug levels.

17.5.10 Laboratory Values.

In JAMA Network journals, laboratory values for clinical chemistry analyses, hematologic tests, immunologic assays, metabolic and endocrine tests, therapeutic drug monitoring, toxicology determinations, and urinalysis are reported by means of conventional laboratory units. Table 17.5-2 provides examples of conventional units and SI units and is intended to facilitate conversion from conventional units to SI units (and vice versa). A conversion calculator is freely available online at www.amamanualofstyle.com.

Laboratory reference values and units vary considerably among individual laboratories and are highly dependent on the analytic methods used. For reports of diagnostic tests or interpretations, the reference range followed by the local laboratory should be included. Several resources6,7,8,9,10 contain detailed information about these topics and tables with laboratory reference values and SI conversion factors.

Table 17.5-2. Selected Laboratory Tests, With Conversion Factorsa

Analyte

Specimen

Conventional unit

Conversion factor (multiply by)

SI unit

Acetaminophen/paracetamol

Serum, plasma

μg/mL

6.614

μmol/L

Acetoacetate

Serum, plasma

mg/dL

97.95

μmol/L

Acetone

Serum, plasma

mg/dL

0.172

mmol/L

Acid phosphatase

Serum

U/L

16.667

nkat/L

Activated partial thromboplastin time (APTT)

Whole blood

s

1.0

s

Adenosine deaminase

Serum

U/L

16.667

nkat/L

Adrenocorticotropic hormone (ACTH)

Plasma

pg/mL

0.22

pmol/L

Alanine

Plasma

mg/dL

112.2

μmol/L

Alanine aminotransferase (ALT)

Serum

U/L

0.0167

μkat/L

Albumin

Serum

g/dL

10

g/L

Alcohol dehydrogenase

Serum

U/L

16.667

nkat/L

Aldolase

Serum

U/L

0.0167

μkat/L

Aldosterone

Serum, plasma

ng/dL

27.74

pmol/L

Alkaline phosphatase

Serum

U/L

0.0167

μkat/L

Alprazolam

Serum, plasma

ng/mL

3.24

nmol/L

Amikacin

Serum, plasma

μg/mL

1.708

μmol/L

α-Aminobutyric acid

Plasma

mg/dL

96.97

μmol/L

δ-Aminolevulinic acid

Serum

μg/dL

0.0763

μmol/L

Amiodarone

Serum, plasma

μg/mL

1.55

μmol/L

Amitriptyline

Plasma

ng/mL

3.605

nmol/L

Ammonia (as nitrogen)

Serum, plasma

μg/dL

0.714

μmol/L

Amobarbital

Serum

μg/mL

4.42

μmol/L

Amphetamine

Serum, plasma

ng/mL

7.4

nmol/L

Amylase

Serum

U/L

0.0167

μkat/L

Androstenedione

Serum

ng/dL

0.0349

nmol/L

Angiotensin I

Plasma

pg/mL

0.772

pmol/L

Angiotensin II

Plasma

pg/mL

0.957

pmol/L

Angiotensin-converting enzyme

Serum

U/L

16.667

nkat/L

Anion gap Na+− (Cl + HCO3)

Serum, plasma

mEq/L

1.0

mmol/L

Antidiuretic hormone (ADH)

Plasma

pg/mL

0.923

pmol/L

Antithrombin III

Plasma

mg/dL

10

mg/L

α1-Antitrypsin

Serum

mg/dL

0.184

μmol/L

Apolipoprotein A-I

Serum

mg/dL

0.01

g/L

Apolipoprotein B

Serum, plasma

mg/dL

0.01

g/L

Arginine

Serum

mg/dL

57.4

μmol/L

Arsenic

Whole blood

μg/L

0.0133

μmol/L

Ascorbic acid (see vitamin C)





Asparagine

Plasma

mg/dL

75.689

μmol/L

Aspartate aminotransferase (AST)

Serum

U/L

0.0167

μkat/L

Aspartic acid

Plasma

mg/dL

75.13

μmol/L

Atrial natriuretic hormone

Plasma

pg/mL

1

ng/L

Bands (see white blood cell count)





Base excess

Whole blood

mEq/L

1.0

mmol/L

Basophils (see white blood cell count)





Bicarbonate

Serum

mEq/L

1.0

mmol/L

Bile acids (total)

Serum

μg/mL

2.448

μmol/L

Bilirubin, direct (conjugated)

Serum

mg/dL

17.104

μmol/L

Bilirubin, total

Serum

mg/dL

17.104

μmol/L

Biotin

Serum

pg/mL

0.00409

nmol/L

Bismuth

Whole blood

μg/L

4.785

nmol/L

Blood gases





Carbon dioxide, PCO2

Arterial blood

mm Hg

0.133

kPa

pH

Arterial blood


1.0


Oxygen, PO2

Arterial blood

mm Hg

0.133

kPa

Brain-type natriuretic peptide (BNP)

Plasma

pg/mL

1.0

ng/L

Bromide (toxic)

Serum

μg/mL

0.0125

mmol/L

C1 esterase inhibitor

Serum

mg/dL

10

mg/L

C3 complement

Serum

mg/dL

0.01

g/L

C4 complement

Serum

mg/dL

0.01

g/L

Cadmium

Whole blood

μg/L

8.896

nmol/L

Caffeine (therapeutic)

Serum, plasma

μg/mL

5.15

μmol/L

Calcitonin

Plasma

pg/mL

0.292

pmol/L

Calcium, ionized

Serum

mg/dL

0.25

mmol/L

Calcium, total

Serum

mg/dL

0.25

mmol/L

Cancer antigen (CA) 125

Serum

U/mL

1.0

kU/L

Carbamazepine

Serum, plasma

μg/mL

4.233

μmol/L

Carbon dioxide (total)

Serum, plasma

mEq/L

1.0

mmol/L

Carboxyhemoglobin, toxic

Whole blood

%

0.01

Proportion of 1.0

Carcinoembryonic antigen (CEA)

Serum

ng/mL

1.0

μg/L

β-Carotene

Serum

μg/dL

0.01863

μmol/L

Carotenoids

Serum

μg/dL

0.01863

μmol/L

Ceruloplasmin

Serum

mg/dL

10

mg/L

Chloramphenicol

Serum

μg/mL

3.095

μmol/L

Chlordiazepoxide

Serum, plasma

μg/mL

3.336

μmol/L

Chloride

Serum, plasma

mEq/L

1.0

mmol/L

Chlorpromazine

Plasma

ng/mL

3.136

nmol/L

Chlorpropamide

Plasma

mg/L

3.61

μmol/L

Cholecalciferol (see vitamin D)





Cholesterol





Total

Serum, plasma

mg/dL

0.0259

mmol/L

High-density lipoprotein (HDL)

Serum, plasma

mg/dL

0.0259

mmol/L

Low-density lipoprotein (LDL)

Serum, plasma

mg/dL

0.0259

mmol/L

Cholinesterase

Serum

U/mL

1.0

kU/L

Chorionic gonadotropin (β-hCG) (nonpregnant)

Serum

mIU/mL

1.0

IU/L

Chromium

Whole blood

μg/L

19.232

nmol/L

Citrate

Serum

mg/dL

52.05

μmol/L

Citrulline

Plasma

mg/dL

57.081

μmol/L

Clonazepam (therapeutic)

Serum

ng/mL

3.167

nmol/L

Clonidine

Serum, plasma

ng/mL

4.35

nmol/L

Clozapine

Serum

ng/mL

0.003

μmol/L

Coagulation factor I

Plasma

g/dL

29.41

μmol/L

(Fibrinogen)

Plasma

mg/dL

0.01

g/L

Coagulation factor II (prothrombin)

Plasma

%

0.01

Proportion of 1.0

Coagulation factor V

Plasma

%

0.01

Proportion of 1.0

Coagulation factor VII

Plasma

%

0.01

Proportion of 1.0

Coagulation factor VIII

Plasma

%

0.01

Proportion of 1.0

Coagulation factor IX

Plasma

%

0.01

Proportion of 1.0

Coagulation factor X

Plasma

%

0.01

Proportion of 1.0

Coagulation factor XI

Plasma

%

0.01

Proportion of 1.0

Coagulation factor XII

Plasma

%

0.01

Proportion of 1.0

Cobalt

Serum

μg/L

16.968

nmol/L

Cocaine (toxic)

Serum

ng/mL

3.297

nmol/L

Codeine

Serum

ng/mL

3.34

nmol/L

Coenzyme Q10 (ubiquinone)

Plasma

μg/mL

1.0

mg/L

Copper

Serum

μg/dL

0.157

μmol/L

Coproporphyrin

Urine

μg/24 h

1.527

μmol/d

Corticotropin

Plasma

pg/mL

0.22

pmol/L

Cortisol

Serum, plasma

μg/dL

27.588

nmol/L

Cotinine

Plasma

μg/L

5.675

nmol/L

C-peptide

Serum

ng/mL

0.331

nmol/L

C-reactive protein

Serum

mg/dL

10

mg/L

Creatine

Serum

mg/dL

76.25

μmol/L

Creatine kinase (CK)

Serum

U/L

0.0167

μkat/L

Creatine kinase—MB fraction

Serum

ng/mL

1.0

μg/L

Creatinine

Serum, plasma

mg/dL

88.4

μmol/L

Creatinine clearance

Serum, plasma

mL/min/1.73 m2

0.0167

mL/s/m2

Cyanide (toxic)

Whole blood

μg/mL

38.4

μmol/L

Cyclic adenosine monophosphate (cAMP)

Plasma

ng/mL

3.04

μmol/L

Cyclosporine

Serum

ng/mL

0.832

nmol/L

Cystine

Plasma

mg/dL

41.615

μmol/L

D-dimer

Plasma

μg/mL

5.476

nmol/L

Dehydroepiandrosterone (DHEA)

Serum

ng/mL

3.47

nmol/L

Dehydroepiandrosterone sulfate (DHEA-S)

Serum

μg/dL

0.027

μmol/L

Deoxycorticosterone

Serum

ng/dL

0.0303

nmol/L

Desipramine

Serum, plasma

ng/mL

3.754

nmol/L

Diazepam

Serum, plasma

ng/mL

0.0035

μmol/L

Digoxin

Plasma

ng/mL

1.281

nmol/L

Diltiazem

Serum

mg/L

2.412

μmol/L

Disopyramide

Serum, plasma

μg/mL

2.946

μmol/L

Dopamine

Plasma

pg/mL

6.528

pmol/L

Doxepin

Serum, plasma

ng/mL

3.579

nmol/L

Electrophoresis (protein)





Proportion of total protein





 Albumin

Serum

%

0.01

Proportion of 1.0

 α1-Globulin

Serum

%

0.01

Proportion of 1.0

 α2-Globulin

Serum

%

0.01

Proportion of 1.0

 β-Globulin

Serum

%

0.01

Proportion of 1.0

 γ-Globulin

Serum

%

0.01

Proportion of 1.0

Concentration





 Albumin

Serum

g/dL

10.0

g/L

 α1-Globulin

Serum

g/dL

10.0

g/L

 α2-Globulin

Serum

g/dL

10.0

g/L

 β-Globulin

Serum

g/dL

10.0

g/L

 γ-Globulin

Serum

g/dL

10.0

g/L

Eosinophils (see white blood cell count)





Ephedrine (toxic)

Serum

μg/mL

6.052

μmol/L

Epinephrine

Plasma

pg/mL

5.459

pmol/L

Erythrocyte count (see red blood cell count)





Erythrocyte sedimentation rate

Whole blood

mm/h

1.0

mm/h

Erythropoietin

Serum

mIU/mL

1.0

IU/L

Estradiol (E2)

Serum

pg/mL

3.671

pmol/L

Estriol (E3)

Serum

ng/mL

3.467

nmol/L

Estrogens (total)

Serum

pg/mL

1.0

ng/L

Estrone (E1)

Serum, plasma

pg/mL

3.698

pmol/L

Ethanol (ethyl alcohol)

Serum, whole blood

mg/dL

0.2171

mmol/L

Ethchlorvynol (toxic)

Serum, plasma

μg/mL

6.915

μmol/L

Ethosuximide

Serum

mg/L

7.084

μmol/L

Ethylene glycol (toxic)

Serum, plasma

mg/dL

0.1611

mmol/L

Fatty acids (nonesterified)

Serum, plasma

mg/dL

0.0355

mmol/L

Fecal fat (as stearic acid)

Stool

g/d

1.0

g/24 h

Fentanyl

Serum

μg/mL

2.972

μmol/L

Ferritin

Serum

ng/mL

1.0

μg/L

α-Fetoprotein (AFP)

Serum

ng/mL

1.0

μg/L

Fibrin degradation products

Plasma

μg/mL

1.0

mg/L

Fibrinogen

Plasma

mg/dL

0.01

g/L

Flecainide

Serum, plasma

μg/mL

2.413

μmol/L

Fluoride

Whole blood

mg/dL

0.5263

mmol/L

Fluoxetine

Serum

ng/mL

0.00323

μmol/L

Flurazepam (toxic)

Serum, plasma

μg/mL

2.578

μmol/L

Folate (folic acid)

Serum

ng/mL

2.266

nmol/L

Follicle-stimulating hormone (FSH)

Serum, plasma

mIU/mL

1.0

IU/L

Fructosamine

Serum

mg/L

5.581

mmol/L

Fructose

Serum

mg/dL

55.506

μmol/L

Galactose

Serum, plasma

mg/dL

0.0555

mmol/L

Gastrin

Serum

pg/mL

0.481

pmol/L

Gentamicin

Serum

μg/mL

2.090

μmol/L

Glucagon

Plasma

pg/mL

1.0

ng/L

Glucose

Serum

mg/dL

0.0555

mmol/L

Glucose-6-phosphate dehydrogenase

Whole blood

U/g of hemoglobin

0.0167

nkat/g hemoglobin

Glutamic acid

Plasma

mg/dL

67.967

μmol/L

Glutamine

Plasma

mg/dL

68.423

μmol/L

γ-Glutamyltransferase (GGT)

Serum

U/L

0.0167

μkat/L

Glutethimide

Serum

μg/mL

4.603

μmol/L

Glycerol (free)

Serum

mg/dL

0.1086

mmol/L

Glycine

Plasma

mg/dL

133.2

μmol/L

Gold

Serum

μg/dL

50.770

nmol/L

Growth hormone (GH)

Serum

ng/mL

1.0

μg/L

Haloperidol

Serum, plasma

ng/mL

2.66

nmol/L

Haptoglobin

Serum

mg/dL

10

mg/L

Hematocrit

Whole blood

%

0.01

Proportion of 1.0

Hemoglobin

Whole blood

g/dL

10.0

g/L

 Mean corpuscular hemoglobin (MCH)

Whole blood

pg/cell

1.0

pg/cell

 Mean corpuscular hemoglobin concentration (MCHC)

Whole blood

g/dL

10

g/L

 Mean corpuscular volume (MCV)

Whole blood

μm3

1.0

fL

Hemoglobin A1c (glycated hemoglobin)

Whole blood

% of total hemoglobin (can be dual-reported as mmol/mol)b

0.01

Proportion of total hemoglobin

Hemoglobin A2

Whole blood

%

0.01

Proportion of 1.0

Histamine

Plasma

μg/L

8.997

nmol/L

Histidine

Plasma

mg/dL

64.45

μmol/L

Homocysteine

Plasma

mg/L

7.397

μmol/L

Homovanillic acid

Urine

mg/24 h

5.489

μmol/d

Hydrocodone

Serum

μg/mL

3.34

μmol/L

Hydromorphone

Serum

μg/mL

3504

nmol/L

β-Hydroxybutyric acid

Plasma

mg/dL

96.06

μmol/L

5-Hydroxyindoleacetic acid (5-HIAA)

Urine

mg/24 h

5.23

μmol/d

Hydroxyproline

Plasma

mg/dL

76.266

μmol/L

Ibuprofen

Serum

μg/mL

4.848

μmol/L

Imipramine

Plasma

ng/mL

3.566

nmol/L

Immunoglobulin A (IgA)

Serum

mg/dL

0.01

g/L

Immunoglobulin D (IgD)

Serum

mg/dL

10

mg/L

Immunoglobulin E (IgE)

Serum

mg/dL

10

mg/L

Immunoglobulin G (IgG)

Serum

mg/dL

0.01

g/L

Immunoglobulin M (IgM)

Serum

mg/dL

0.01

g/L

Insulin

Serum

μIU/mL

6.945

pmol/L

Insulinlike growth factor

Serum

ng/mL

0.131

nmol/L

Iodine

Serum

μg/L

7.880

nmol/L

Iron

Serum

μg/dL

0.179

μmol/L

Iron-binding capacity

Serum

μg/dL

0.179

μmol/L

Isoleucine

Plasma

mg/dL

76.236

μmol/L

Isoniazid

Plasma

μg/mL

7.291

μmol/L

Isopropanol (toxic)

Serum, plasma

mg/L

0.0166

mmol/L

Kanamycin

Serum, plasma

μg/mL

2.064

μmol/L

Ketamine

Serum

μg/mL

4.206

μmol/L

17-Ketosteroids

Urine

mg/24 h

3.33

μmol/d

Lactate

Plasma

mg/dL

0.111

mmol/L

Lactate dehydrogenase (LDH)

Serum

U/L

0.0167

μkat/L

LDH isoenzymes





LD1

Serum

%

0.01

Proportion of 1.0

LD2

Serum

%

0.01

Proportion of 1.0

LD3

Serum

%

0.01

Proportion of 1.0

LD4

Serum

%

0.01

Proportion of 1.0

LD5

Serum

%

0.01

Proportion of 1.0

Lead

Serum

μg/dL

0.0483

μmol/L

Leucine

Plasma

mg/dL

76.237

μmol/L

Leukocytes (see white blood cell count)





Lidocaine

Serum, plasma

μg/mL

4.267

μmol/L

Lipase

Serum

U/L

0.0167

μkat/L

Lipoprotein(a) [Lp(a)]c

Serum

mg/dL

0.1

mg/L

Lithium

Serum

mEq/L

1.0

mmol/L

Lorazepam

Serum

ng/mL

3.114

nmol/L

Luteinizing hormone (LH)

Serum, plasma

mIU/mL

1.0

IU/L

Lycopene

Serum

mg/L

1.863

μmol/L

Lymphocytes (see white blood cell count)





Lysergic acid diethylamide (LSD)

Serum

μg/mL

3092

nmol/L

Lysine

Plasma

mg/dL

68.404

μmol/L

Lysozyme

Serum, plasma

mg/dL

10

mg/L

Magnesium

Serum

mg/dL

0.4114

mmol/L

Manganese

Whole blood

μg/L

18.202

nmol/L

Maprotiline

Plasma

ng/mL

1.0

μg/L

Melatonin

Serum

ng/L

4.305

pmol/L

Meperidine

Serum, plasma

ng/mL

4.043

nmol/L

Mercury

Serum

μg/L

4.985

nmol/L

Metanephrine (total)

Urine

mg/24 h

5.07

μmol/d

Metformin

Serum

μg/mL

7.742

μmol/L

Methadone

Serum, plasma

ng/mL

0.00323

μmol/L

Methamphetamine

Serum

μg/mL

6.7

μmol/L

Methanol

Plasma

μg/mL

0.0312

mmol/L

Methaqualone

Serum, plasma

μg/mL

3.995

μmol/L

Methemoglobin

Whole blood

g/dL

155

μmol/L

Methemoglobin

Whole blood

% of total hemoglobin

0.01

Proportion of total hemoglobin

Methicillin

Serum

mg/L

2.636

μmol/L

Methionine

Plasma

mg/dL

67.02

μmol/L

Methotrexate

Serum, plasma

mg/L

2200

nmol/L

Methyldopa

Plasma

μg/mL

4.735

μmol/L

Metoprolol

Serum, plasma

ng/mL

3.74

nmol/L

β2-Microglobulin

Serum

mg/L

1.0

mg/L

Morphine

Serum, plasma

ng/mL

3.504

nmol/L

Myoglobin

Serum

μg/L

0.05814

nmol/L

Naproxen

Serum

μg/mL

4.343

μmol/L

Niacin (nicotinic acid)

Urine

mg/24 h

8.123

μmol/d

Nickel

Whole blood

μg/L

17.033

nmol/L

Nicotine

Plasma

mg/L

6.164

μmol/L

Nitrogen (nonprotein)

Serum

mg/dL

0.714

mmol/L

Nitroprusside (as thiocyanate)


μg/mL

17.2

μmol/L

Norepinephrine

Plasma

pg/mL

5.911

pmol/L

Nortriptyline

Serum, plasma

ng/mL

3.797

nmol/L

Ornithine

Plasma

mg/dL

75.666

μmol/L

Osmolality

Serum

mOsm/kg

1.0

mmol/kg

Osteocalcin

Serum

ng/mL

1.0

μg/L

Oxalate

Serum

mg/mL

11.107

μmol/L

Oxazepam

Serum, plasma

μg/mL

3.487

μmol/L

Oxycodone

Serum

ng/mL

3.171

nmol/L

Oxygen, partial pressure (Po2)

Arterial blood

mm Hg

0.133

kPa

Paraquat

Whole blood

μg/mL

5.369

μmol/L

Parathyroid hormone

Serum

pg/mL

1

ng/L

Pentobarbital

Serum, plasma

μg/mL

4.419

μmol/L

Pepsinogen

Serum

ng/mL

1.0

μg/L

pH (see blood gases)





Phencyclidine (toxic)

Serum, plasma

ng/mL

4.109

nmol/L

Phenobarbital

Serum, plasma

μg/mL

4.31

μmol/L

Phenylalanine

Plasma

mg/dL

60.544

μmol/L

Phenylpropanolamine

Serum

μg/mL

6613

nmol/L

Phenytoin

Serum, plasma

mg/L

3.968

μmol/L

Phosphorus (inorganic)

Serum

mg/dL

0.323

mmol/L

Placental lactogen

Serum

μg/mL

46.296

nmol/L

Plasminogen (antigenic)

Plasma

mg/dL

0.113

μmol/L

Plasminogen activator inhibitor

Plasma

ng/mL

22.19

pmol/L

Platelet count (thrombocytes)

Whole blood

×103/μL

1.0

×109/L

Potassium

Serum

mEq/L

1.0

mmol/L

Prealbumin

Serum

mg/dL

10

mg/L

Pregnanediol

Urine

mg/24 h

3.12

μmol/d

Pregnanetriol

Urine

mg/24 h

2.972

μmol/d

Primidone

Serum, plasma

μg/mL

4.582

μmol/L

Procainamide

Serum, plasma

μg/mL

4.25

μmol/L

Progesterone

Serum

ng/mL

3.18

nmol/L

Prolactin

Serum

ng/mL

1

μg/L

Proline

Plasma

mg/dL

86.858

μmol/L

Propoxyphene

Plasma

μg/mL

2.946

μmol/L

Propranolol

Serum

ng/mL

3.856

nmol/L

Prostate-specific antigen

Serum

ng/mL

1.0

μg/L

Protein (total)

Serum

g/dL

10.0

g/L

Prothrombin time (PT)

Plasma

s

1.0

s

Protoporphyrin

Red blood cells

μg/dL

0.0178

μmol/L

Protriptyline

Serum, plasma

μg/dL

3.787

nmol/L

Pyridoxine (see vitamin B6)





Pyruvate

Plasma

mg/dL

113.56

μmol/L

Quinidine

Serum

μg/mL

3.082

μmol/L

Red blood cell count

Whole blood

×106/μL

1.0

×1012/L

Renin

Plasma

pg/mL

0.0237

pmol/L

Reticulocyte count

Whole blood

×103/μL

1.0

×109/L

Reticulocyte count

Whole blood

% of red blood cells

0.01

Proportion of red blood cells

Retinol (see vitamin A)





Riboflavin (see vitamin B2)





Rifampin

Serum

mg/L

1.215

μmol/L

Salicylates

Serum, plasma

μg/mL

7.24

μmol/L

Selenium

Serum, plasma

μg/L

0.0127

μmol/L

Serine

Plasma

mg/dL

95.156

μmol/L

Serotonin (5-hydroxytryptamine)

Whole blood

ng/mL

0.00568

μmol/L

Sex hormone—binding globulin

Serum

μg/mL

8.896

nmol/L

Sodium

Serum

mEq/L

1.0

mmol/L

Somatomedin C (insulinlike growth factor)

Serum

ng/mL

0.131

nmol/L

Somatostatin

Plasma

pg/mL

0.611

pmol/L

Streptomycin

Serum

mg/L

1.719

μmol/L

Strychnine

Whole blood

mg/L

2.99

μmol/L

Substance P

Plasma

pg/mL

0.742

pmol/L

Sulfate

Serum

mg/L

10.41

μmol/L

Sulfmethemoglobin

Whole blood

% of total hemoglobin

0.01

Proportion of total hemoglobin

Taurine

Plasma

mg/dL

79.91

μmol/L

Testosterone

Serum

ng/dL

0.0347

nmol/L

Tetrahydrocannabinol

Serum

μg/mL

3.180

μmol/L

Theophylline

Serum, plasma

μg/mL

5.55

μmol/L

Thiamine (see vitamin B1)





Thiopental

Serum, plasma

μg/mL

4.144

μmol/L

Thioridazine

Serum, plasma

μg/mL

2.699

μmol/L

Threonine

Plasma

mg/dL

84

μmol/L

Thrombin time

Plasma

s

1.0

s

Thrombocytes (see platelet count)





Thyroglobulin

Serum

ng/mL

1.0

μg/L

Thyrotropin

Serum

mIU/L

1.0

mIU/L

Thyroxine, free (FT4)

Serum

ng/dL

12.87

pmol/L

Thyroxine, total (T4)

Serum

μg/dL

12.87

nmol/L

Thyroxine-binding globulin

Serum

μg/mL

17.094

nmol/L

Tissue plasminogen activator

Plasma

IU/mL

1000

IU/L

Tobramycin

Serum, plasma

μg/mL

2.139

μmol/L

Tocainide

Serum

μg/mL

5.201

μmol/L

α-Tocopherol (see vitamin E)





Tolbutamide

Serum

μg/mL

3.70

μmol/L

Transferrin

Serum

mg/dL

0.123

μmol/L

Triglycerides

Serum

mg/dL

0.0113

mmol/L

Triiodothyronine, free (FT3)

Serum

pg/dL

0.0154

pmol/L

Triiodothyronine, total (T3)

Serum

ng/dL

0.0154

nmol/L

Troponin I

Serum

ng/mL

1.0

μg/L

Troponin T

Serum

ng/mL

1.0

μg/L

Tryptophan

Plasma

mg/dL

48.967

μmol/L

Tyrosine

Plasma

mg/dL

55.19

μmol/L

Urea nitrogen

Serum

mg/dL

0.357

mmol/L

Uric acid

Serum

mg/dL

0.0595

mmol/L

Urobilinogen

Urine

mg/24 h

1.7

μmol/d

Valine

Plasma

mg/dL

85.361

μmol/L

Valproic acid

Serum, plasma

μg/mL

6.934

μmol/L

Vancomycin

Serum, plasma

μg/mL

0.690

μmol/L

Vanillylmandelic acid (VMA)

Urine

mg/24 h

5.046

μmol/d

Vasoactive intestinal polypeptide

Plasma

pg/mL

0.296

pmol/L

Vasopressin

Plasma

pg/mL

0.923

pmol/L

Verapamil

Serum, plasma

ng/mL

2.20

nmol/L

Vitamin A (retinol)

Serum

μg/dL

0.0349

μmol/L

Vitamin B1 (thiamine)

Serum

μg/dL

29.6

nmol/L

Vitamin B2 (riboflavin)

Serum

μg/dL

26.6

nmol/L

Vitamin B3

Whole blood

μg/mL

4.56

μmol/L

Vitamin B6 (pyridoxine)

Plasma

ng/mL

4.046

nmol/L

Vitamin B12

Serum

pg/mL

0.7378

pmol/L

Vitamin C (ascorbic acid)

Serum

mg/dL

56.78

μmol/L

Vitamin D (1,25-dihydroxyvitamin D)

Serum

pg/mL

2.4

pmol/L

Vitamin D (25-hydroxyvitamin D)

Plasma

ng/mL

2.496

nmol/L

Vitamin E (α-tocopherol)

Serum

μg/mL

2.322

μmol/L

Vitamin K

Serum

ng/mL

2.22

nmol/L

Warfarin

Serum, plasma

μg/mL

3.247

μmol/L

White blood cell count

Whole blood

/μL

0.001

×109/L

Differential count





 Neutrophils—segmented

Whole blood

/μL

0.001

×109/L

 Neutrophils—bands

Whole blood

/μL

0.001

×109/L

 Lymphocytes

Whole blood

/μL

0.001

×109/L

 Monocytes

Whole blood

/μL

0.001

×109/L

 Eosinophils

Whole blood

/μL

0.001

×109/L

 Basophils

Whole blood

/μL

0.001

×109/L

Differential count (number fraction)





 Neutrophils—segmented

Whole blood

%

0.01

Proportion of 1.0

 Neutrophils—bands

Whole blood

%

0.01

Proportion of 1.0

 Lymphocytes

Whole blood

%

0.01

Proportion of 1.0

 Monocytes

Whole blood

%

0.01

Proportion of 1.0

 Eosinophils

Whole blood

%

0.01

Proportion of 1.0

 Basophils

Whole blood

%

0.01

Proportion of 1.0

Zidovudine

Serum, plasma

μg/mL

3.7

μmol/L

Zinc

Serum

μg/dL

0.153

μmol/L

a The laboratory values are provided for illustration only and are not intended to be comprehensive or definitive. Each laboratory determines its own values. The information in this table is adapted from and based on the following sources: Kratz et al,6 Young and Huth,7 McPherson and Pincus,8 Goldman and Schaeffer,9 Longo et al,10 Lipoprotein a Foundation,11 and Laposata.12

b Most laboratories do not convert to molar units; conversion of Lp(a) is difficult unless the size (large or small) of an individual’s Lp(a) molecules is known.

c For dual reporting hemoglobin A1c (HbA1c) as both a percentage of total hemoglobin and mmol HbA1c/mol Hb, see the NGSP website IFCC Standardization of HbA1c.13

For laboratory values reported in JAMA Network journals, factors for converting conventional units to SI units should be provided in the article. In text, the conversion factor should be given once, at first mention of the laboratory value, in parentheses following the conventional unit.

The blood glucose concentration of 126 mg/dL (to convert to mmol/L, multiply by 0.0555) was used as a criterion for diagnosing diabetes.

For articles in which several laboratory values are reported in text, the conversion factors may be listed in a paragraph at the end of the Methods section but not in the abstract of the article. For figures or tables, the conversion factors should be included in legends or in footnotes, respectively, (see 4.1.3.10, Footnotes). For articles in which there is no Methods section, conversion factors can be given at first mention of the value, and reference ranges for the local laboratory can be included as well.

When the results were returned, serum ammonia levels were markedly elevated at 643 µg/dL (to convert to µmol/L, multiply by 0.714). A subsequent hepatic panel was notable for mildly elevated levels of alanine aminotransferase (89 U/L; to convert to µkat/L, multiply by 0.0167) and γ-glutamyltransferase (81 U/L; to convert to µkat/L, multiply by 0.0167).

Hematologic values should be reported by means of conventional units.

The complete blood cell count showed a hemoglobin level of 13.4 g/dL, hematocrit of 41%, platelet count of 180 000/μL, and white blood cell count of 6500/μL.

Standardization is emerging for reporting hemoglobin A1c,13 and we recommend dual reporting, as shown in Table 17.5-3.

Table 17.5-3. Primary End Points

Primary end point

CGM, mean (95% CI)

Conventional therapy, mean (95% CI)

Least square means or mean for difference: CGM−conventional treatment (95% CI)

P value

HbA1c, %a

7.92 (7.79 to 8.05)

8.35 (8.19 to 8.51)

−0.43 (−0.57 to −0.29)

<.001

HbA1c, mmol/mol

63 (61.6 to 64.5)

68 (66.0 to 69.4)

−4.7 (−6.27 to −3.13)


Abbreviations: CGM, continuous glucose monitoring; HbA1c, hemoglobin A1c.

SI conversion factor: To convert percentage of total hemoglobin to proportion of total hemoglobin, multiply by 0.01.

a Values are reported as last observation carried forward with HbA1c measurement standardized by NGSP (http://www.ngsp.org/ifccngsp.asp).

For enzymatic activity, the international unit (IU) is used; 1 IU equals the amount of enzyme generating 1  μmol of product per minute.

The peak follicle-stimulating hormone level was 48 mIU/mL.

17.5.11 Radiation.

Measurements of ionizing radiation and radioactivity should be reported by means of SI units. The SI units for radiation are established by international agreement.2 The unit for activity of a radionuclide is the becquerel; the absorbed dose of radiation (absorbed per unit weight of tissue) is the gray (Gy); and the dose equivalent used to indicate the detrimental effects of an absorbed radiation dose on biological tissue is the sievert (Sv).

A 1-Gy dose is equivalent to 1 joule (J) of radiation energy absorbed per kilogram of organ or tissue weight. The rad is the older, non-SI unit and is still in use as a unit of absorbed dose (100 rad   =  1 Gy). However, equal doses of all types of ionizing radiation are not equally harmful. Alpha particles produce greater harm than beta particles, γ rays, and x-rays for a given absorbed dose. To account for this difference, radiation dose is expressed as equivalent dose in sieverts (Sv).14

SI units for radiation and factors to convert values from SI units to conventional units are given in Table 17.5-4.

Table 17.5-4. Measurement Units for Radiation, With Conversion Factors

Quantity

SI unit (symbol)

Conversion factors

Non-SI unit

Radioactivity

becquerel (Bq)

1 Bq = 2.7 × 10−11 Ci (approx) 1 Ci = 3.7 × 1010 Bq 1 Bq = 27 picocurie (pCi)

curie (Ci)

Absorbed dose

gray (Gy)

1 Gy = 100 rad 1 rad = 0.01 Gya

rad

“Dose” equivalent

sievert (Sv)

1 Sv = 100 rem 1 rem = 0.01 Sv

rem

a Although 1 rad = 1 cGy, the prefix centi- is generally not preferred in SI. Therefore, despite the appeal of one-to-one conversion, rad should be converted to gray not centigray.

Although SI units are preferred, authors of some articles, such as those reporting studies that involve nuclear medicine or radiation oncology, may prefer to report results in both SI units and non-SI units. As with units for laboratory results, conversion factors to convert radiation from SI units to conventional units should be provided in the text, footnotes to tables or figures, and/or the Methods section of the article.

17.5.12 Currency.

Amounts of money are expressed as a decimal number or whole number preceded by the symbol for the unit of measure for the currency.

The cost-effectiveness analysis suggested a $7000 difference between the 2 treatment strategies.

Table 17.5-5 lists some international currencies and their symbols. Online currency converter programs are also available.15,16

Table 17.5-5. Selected International Currencies and Symbols

Country

Currency

Symbol or abbreviation

Argentina

Argentine peso

$

Australia

Australian dollar

A$

Austria

euro

Bahamas

Bahamian dollar

B$

Belgium

euro

Bermuda

Bermuda dollar

Bd$

Bolivia

boliviano

$

Brazil

Brazilian real

R$

Canada

Canadian dollar

CAD$

Chile

Chilean peso

Ch$

China

yuan renminbi

¥

Colombia

Colombian peso

Col$

Cuba

Cuban peso

$

Czech Republic

Czech koruna

Denmark

Danish krone

kr

Dominican Republic

Dominican peso

RD$

Egypt

Egyptian pound

£

Ethiopia

Ethiopian birr

ብር

European Union

euro

Finland

euro

France

euro

Germany

euro

Ghana

Ghana cedi

GH¢

Greece

euro

Hong Kong

Hong Kong dollar

HK$

Hungary

forint

ft

India

rupee

Iran

rial

IRR

Iraq

new Iraqi dinar

IQD

Ireland

euro

Israel

Israeli new sheqel

Italy

euro

Japan

yen

¥

Jordan

Jordanian dinars

JD

Lebanon

Lebanese pound

LBP

Luxembourg

euro

Malawi

kwacha

MK

Mexico

Mexican peso

Mex$

The Netherlands

euro

New Zealand

New Zealand dollar

NZ$

Nigeria

naira

Norway

Norwegian krone

kr

Pakistan

rupee

Rs

Peru

nuevos soles

S/

Poland

zloty

Zl

Portugal

euro

Russia

ruble

R

Saudi Arabia

Saudi riyal

SR

Singapore

Singapore dollar

SGD

South Africa

rand

R

South Korea

won

Spain

euro

Sweden

Swedish krona

Sk

Switzerland

Swiss franc

CHF

Taiwan

Taiwanese new dollar

NT$

Thailand

baht

฿

Turkey

Turkish new lira

Uganda

shilling

USh

Ukraine

hryvnia

United Kingdom

pound sterling

£

United States of America

US dollar

$

Vietnam

dong

Zambia

kwacha

ZK

Zimbabwe

dollar

$

For amounts reported in non-US currency, the current exchange rate should be used to calculate the amount in US dollars, and that amount should be shown in parentheses.

The baseline amount for the cost-benefit analysis was estimated from the procedure cost of CAD $3000 (US $2800).

The projected cost of the new research laboratory was €25 million (US $47.7 million).

The following example shows how the currency appears as a unit of measure in a table stub.

Household income, CAD$

Principal Authors: Lauren Fischer and Paul Frank

Acknowledgment

James C. Boyd, MD, University of Virginia Health System, Charlottesville, provided careful review of the SI conversion factors table. Hope J. Lafferty, AM, ELS, Hope J. Lafferty Communications, Marfa, Texas; Trevor Lane, MA, DPhil, Edanz Group, Fukuoka, Japan; Rochelle Lodder, formerly of JAMA Network; and Peter J. Olson, ELS, Sheridan Services, Waterbury, Vermont, provided input on an earlier version of the chapter.

References

1.Arbesman S. Liters and followers. Wall Street Journal. August 2, 2014:C6.

2.Bureau International des Poids et Mesures. The International System of Units (SI). 9th ed. Updated 2019. Accessed August 18, 2019. https://www.bipm.org/en/publications/si-brochure/

3.Thompson A, Taylor BN. Guide for the Use of the International System of Units (SI). National Institute of Standards and Technology, US Dept of Commerce; 2008. Accessed September 23, 2015. https://physics.nist.gov/cuu/pdf/sp811.pdf

4.Dorland’s Illustrated Medical Dictionary. 32nd ed. Elsevier Saunders; 2012.

5.Kriska AM, Caspersen CJ. Introduction to a collection of physical activity questionnaires. Med Sci Sports Exerc. 1997;29(6):S5-S9.

6.Kratz A, Ferraro M, Sluss PM, Lewandrowski KB. Normal reference laboratory values. N Engl J Med. 2004;351(15):1548-1563. doi:10.1056/NEJMcpc049016

7.Young DS, Huth EJ. SI Units for Clinical Measurement. American College of Physicians; 1998.

8.McPherson R, Pincus M, eds. Henry’s Clinical Diagnosis and Management by Laboratory Methods. 22nd ed. Elsevier Saunders; 2012.

9.Goldman L, Schaeffer AI. Goldman-Cecil Medicine. 25th ed. Elsevier Saunders; 2015.

10.Longo D, Fauci A, Kasper D, Hauser S, Jameson J, Loscalzo J, eds. Harrison’s Principles of Internal Medicine. 18th ed. McGraw-Hill Professional; 2011.

11.Lipoprotein a Foundation. Understand inherited lipoprotein(a). May 2017. Accessed August 1, 2019. https://www.lipoproteinafoundation.org/page/UnderstandLpa

12.Laposta M, ed. Laboratory Medicine: The Diagnosis of Disease in the Clinical Laboratory. 2nd ed. McGraw-Hill Education; 2014.

13.NGSP website. IFCC Standardization of HbA1c. 2010. Accessed June 30, 2017. http://www.ngsp.org/ifccngsp.asp

14.Canadian Centre for Occupational Health and Safety. What is ionizing radiation? Accessed September 23, 2015. https://www.ccohs.ca/oshanswers/phys_agents/ionizing.html

15.ISO 4217 Currency codes. International Organization for Standardization; 2017. Accessed July 5, 2019. https://www.iso.org/iso-4217-currency-codes.html

16.Oanda.com Currency Converter. Accessed September 23, 2015. https://www.oanda.com/currency/converter