AMA Manual of Style - Stacy L. Christiansen, Cheryl Iverson 2020
Greek Letter vs Word
Greek letters are frequently used in statistical formulas and notations, mathematical composition, certain chemical names for drugs, and clinical and technical terms (see 13.12, Units of Measure; 14.0, Nomenclature; 19.0, Study Design and Statistics; and 20.0, Mathematical Composition).
κ light chain
κ/ λ light-chain ratio
16.1 Greek Letter vs Word.
Use of Greek letters rather than spelled-out words is preferred, unless common usage dictates otherwise (eg, tau protein). Consult Dorland’s and Stedman’s medical dictionaries for general terms. However, these sources may differ in the representation of terms (eg, α-fetoprotein in Stedman’s and alpha fetoprotein in Dorland’s).
For chemical terms, the use of Greek letters is almost always preferred.
ω-3 fatty acids
For electroencephalographic terms, use the word (see 14.11.2, Electroencephalographic Terms).
The electroencephalographic activity showed 2 spectral peaks: one in the theta range and the other at higher frequencies (25-50 Hz).
For drug names that contain Greek letters, consult the sources listed in 14.4, Drugs, for preferred usage. In some cases, when the Greek letter is part of the word (as in betamethasone), the Greek letter is spelled out and set closed up. For some drug names, the approved nonproprietary name uses the word and not the letter, with an intervening space (as in beta carotene). (However, the chemical name for beta carotene is β-carotene.) Other drug names use the Greek letter (as in β-lactam antibiotics).