Biomarker Library

What the number means, and what it does not

Biomarkers are useful precisely to the degree you understand their limits. Each entry states what the marker measures and, separately, what it cannot tell you.

Measures and limitations, side by side
No reference ranges or targets

These are explanations of what markers measure — not reference ranges, not targets, and not a basis for changing anything. Interpreting your results requires a clinician who knows your history. Optimising a number is not the same as improving your health.

Panel

Glucose regulation

HbA1c

Measures. Reflects average glucose exposure over roughly three months.

Limitation. Distorted by anything that changes red-cell lifespan — anaemia, haemoglobin variants, recent blood loss.

Fasting insulin

Measures. Used to infer insulin resistance, often via HOMA-IR.

Limitation. Assay methods are not standardised between laboratories, so absolute values are hard to compare across sites.

Continuous glucose monitoring

Measures. Shows glucose variability that point measurements miss.

Limitation. In people without diabetes, the clinical meaning of most variability metrics is not established.

Panel

Cardiovascular risk

ApoB

Measures. Counts atherogenic particles directly rather than inferring from cholesterol content.

Limitation. A risk marker, not a diagnosis. It informs a decision; it does not make one.

Lp(a)

Measures. Largely genetically determined and measured once in most people.

Limitation. Few interventions change it meaningfully, which limits what a repeat measurement adds.

hs-CRP

Measures. A non-specific marker of systemic inflammation.

Limitation. Rises with any recent infection, injury or intense exercise. A single elevated value usually means very little.

Panel

Body composition and ageing

DEXA lean mass

Measures. Tracks lean tissue — particularly relevant during rapid weight loss.

Limitation. Scan-to-scan variability and hydration status can produce changes that are not real tissue changes.

VO2 max

Measures. Among the strongest single predictors of all-cause mortality in observational data.

Limitation. Observational. Improving it is sensible on many grounds; the causal share of that association is debated.

Epigenetic age clocks

Measures. Research tools estimating biological age from methylation patterns.

Limitation. Substantial measurement variability, and no clock has been validated as a treatment target. Treat results as interesting, not actionable.