Reference Intervals for Plasma Apolipoprotein B: Results From the Framingham Offspring Study

A blood test is only useful once you know what counts as normal and what counts as worrying. This Framingham study did that foundational work for apolipoprotein B — establishing the reference ranges and risk thresholds that later made apoB clinically usable.

Using a standardized commercial assay in nearly 4,000 participants, the investigators defined population reference intervals (with men running higher than women) and identified an apoB of about 1.20 g/L (120 mg/dL) as a high-risk cutpoint — roughly equivalent to an LDL of 160 mg/dL. People above that threshold had significantly more coronary disease.

The significance is infrastructural. Before a marker can guide care, it needs a reliable assay and agreed-upon cutoffs; this study supplied both for apoB, helping move it from research curiosity toward a test a clinician could order and interpret.

We rate the evidence strong for its purpose. It is a careful, well-powered reference study; its clinical significance is high precisely because the thresholds it established underpin the apoB-based risk assessment now endorsed by consensus statements.