Why Is My LDL Different From My Doctor's?

2 min read

8/13/26

Key Takeaways

LDL-C can be calculated (Friedewald, Martin-Hopkins, Sampson-NIH) or measured directly and the approaches don't always agree.
Rythm uses Friedewald: the FDA-recognized clinical standard, validated across the major trials that set today's cardiovascular cutoffs.
CLIA allows up to ±20% between labs on directly measured LDL from the same sample. Track trends within one method.

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Biomarkers

Why Is My LDL Different From My Doctor's?

2 min read

8/13/26

Key Takeaways

LDL-C can be calculated (Friedewald, Martin-Hopkins, Sampson-NIH) or measured directly and the approaches don't always agree.
Rythm uses Friedewald: the FDA-recognized clinical standard, validated across the major trials that set today's cardiovascular cutoffs.
CLIA allows up to ±20% between labs on directly measured LDL from the same sample. Track trends within one method.

Calculated vs. Measured

Most LDL results you've ever received were calculated from total cholesterol, HDL, and triglycerides. Different equations and direct assays can produce different numbers from the same blood, especially when triglycerides are high or LDL is very low. Add machine, brand, and calibration differences, and two “correct” results can sit noticeably apart, all within federally acceptable limits.

Why Rythm Chose Friedewald

Friedewald has been the clinical standard for decades: simple, reliable, FDA-recognized, and crucially the equation used in the large trials that established the risk cutoffs your doctor uses today. Rythm also pairs LDL-C with ApoB, remnant cholesterol, and derived ratios, so you're never relying on a single lens to judge cardiovascular health.

How to Compare Fairly

Match the method, the lab, and the fasting state before you compare numbers and remember the ±20% CLIA window for direct LDL. A different number isn't a wrong number. An LDL of 120 mg/dL on one lab could come back anywhere from 96 to 144 mg/dL on the same sample at another lab, both "accurate" under CLIA. For decision-quality, stick with one method over time; that's what Rythm's repeat panel is built for.

Frequently Asked Questions

How is Rythm different?

Most blood testing companies charge $500 or more for a single test per biomarker, providing only a one-time snapshot that doesn’t capture your long-term health trends or reflect your true baseline. This approach can lead to missed patterns or even misdiagnoses due to limited data. Rythm takes a different approach, using monthly tracking to build a detailed picture of your health over time. This allows for more accurate insights, better optimization, and a clearer understanding of how your body is evolving.

Does Rythm help me improve?

Rythm provides actionable suggestions and tips to help you optimize each biomarker

Is Rythm HIPAA compliant?

Yes, Rythm is HIPAA compliant. Your data is securely stored and handled in accordance with strict privacy and security standards.

Can I cancel anytime without fees?

Yes, you can cancel anytime without any fees.

Does Rythm accept HSA/FSA payments?

Yes, Rythm is HSA/FSA eligible. You can use your HSA or FSA card at checkout or submit your Rythm receipt to your provider for reimbursement.

How long does it take to get my results?

You will receive your results within 3 business days – as long as it's returned within 7 days of receiving your kit. Delays can occur if you do not send your sample back in time.