Biotin can push a blood result too high or too low, by test type
Many lab tests capture what they measure using biotin. Extra biotin competes for that capture: in one test format the result reads too high, in another too low.
What the study found
Which way biotin breaks a blood test is set by the test's design
Many lab tests capture what they measure using biotin bound to streptavidin, a protein, so biotin in the blood competes for that capture. In a competitive-format test the excess reads as more of the substance; in a sandwich-format test it reads as less. Same vitamin, opposite errors.
The caveat · Trigger level differs by test
The direction rule is settled; the amount of biotin needed to trigger it is not. That threshold differs by manufacturer, by test and by how recent the reagent is, and cannot be predicted from one analyser to another. The panel study behind it added biotin to pooled serum in a laboratory rather than measuring people who had swallowed any.