Three Things Drive Most Differences

Method differences. LDL cholesterol can be calculated (Friedewald, Martin-Hopkins, Sampson-NIH) or measured directly, and those approaches don't always agree especially with high triglycerides or very low LDL. Rythm uses the Friedewald calculation because it has been the clinical standard for decades: FDA-recognized, reliable, and validated across the large trials that set today's cardiovascular risk cutoffs. Vitamin D assays vary by platform, which is why Rythm runs it on the Roche cobas pro, a clinically and FDA-validated analyzer with stable calibration.

Instrument and lab factors. Rythm's lab runs the same FDA-approved instruments and analyzers as the major clinical reference labs, validated under CLIA, CAP, and CLEP.

Biology. Fasting status, time of day (TSH, testosterone), menstrual phase (estradiol, progesterone), illness (CRP, ferritin), supplements (i.e large quantities of biotin), and recent heavy exercise all move numbers often more than the analyzer does.

Why “Identical” Was Never the Standard

Even the same sample run twice on the same analyzer show differences,CLIA actually defines how far two labs can differ on the same specimen and still both be considered fully accurate.

So How Should You Compare Labs?

Apples to apples: same fasting state, same time of day, same phase of the menstrual cycle, same lab, same methodology. For analytes without CLIA limits ApoB, SHBG, free T3, vitamin D, look for CDC/CAP standardization participation and rely on trend tracking within one method. Even in traditional medicine, hospital labs and reference labs routinely disagree by several percent on the same biomarkers; that's why clinicians emphasize trends over exact numerical matching.

As an at-home testing company, we hold ourselves to a higher bar to prove our results are as reliable as any traditional clinical lab's. If a result seems genuinely discrepant or unusual, message our team we'll investigate.