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

# Conventional Units and SI Units in JAMA Network JournalsUnits 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.

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 Kč 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 T£ 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.

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