Sources policy
Which documents the reference relies on and how a link earns its place on a page.
The hierarchy
For the English version, materials rely on open professional sources: MedlinePlus (U.S. National Library of Medicine) test encyclopedias and test pages, the UK National Health Service patient guidance, NICE guidance, the LOINC terminology, and ARUP Consult clinical topics. National equivalents serve the other language versions.
The verification rule
A source appears in an article's sources block only after an editor has opened the page and checked the facts against it. Links are never added from memory, from search snippets, or “by analogy”. An empty sources list is better than an invented one: when no verified source exists for a number, the number does not appear on the page.
Access dates
Each entry in a sources block carries the date the page was opened and checked. Medicine changes, so dates matter: they tell the reader which version of the source the text rests on.
What sources do not decide
Reference ranges printed by your own laboratory always outrank any range published here, because laboratories use different measurement methods. Our pages explain how to read a result; they never override your report.