ApoB Conversion Calculator: nmol/L to mg/dL

What Is Apolipoprotein B (ApoB)?

Apolipoprotein B (ApoB) is the main structural protein found on all atherogenic (artery-damaging) lipoprotein particles. Every LDL, IDL, VLDL, and Lp(a) particle carries exactly one ApoB molecule. Because of this one-to-one relationship, measuring ApoB provides a direct count of the total number of atherogenic particles in the blood — something that LDL-cholesterol (LDL-C) does not do.

LDL-C measures the mass of cholesterol carried within LDL particles. ApoB measures the number of particles themselves. This distinction is clinically important because atherosclerotic risk generally tracks more closely with the number of ApoB-containing particles than with the cholesterol mass alone, especially when LDL-C and ApoB are discordant.

ApoB exists in two forms: ApoB-100, produced by the liver and present on VLDL, IDL, LDL, and Lp(a) particles; and ApoB-48, produced by the intestine and present on chylomicrons and their remnants. Routine laboratory ApoB assays measure total ApoB and do not distinguish between these forms. In usual fasting samples, circulating ApoB is predominantly ApoB-100. Importantly, ApoB testing does not require fasting for accurate measurement — unlike LDL-C calculations, which can be unreliable in non-fasting samples or when triglycerides are elevated.

Why ApoB Is a Better Marker Than LDL-C

At the population level, LDL-C, non-HDL-C, and ApoB are usually strongly correlated. In individual patients, however, important discordance can occur — meaning the two measurements give different risk signals. When LDL-C and ApoB disagree, ASCVD risk generally aligns better with ApoB or non-HDL-C than with LDL-C alone. This discordance has major clinical consequences.

When Discordance Occurs

Discordance between LDL-C and ApoB is most common in patients with cholesterol-depleted LDL particles — small, dense LDL that carry less cholesterol per particle. These patients may have an LDL-C that appears at goal, while their ApoB remains elevated, indicating a high number of atherogenic particles and persistent cardiovascular risk. This pattern is particularly common in patients with metabolic syndrome, type 2 diabetes, insulin resistance, obesity, elevated triglycerides, chronic kidney disease, and in patients already on statin therapy.

The 2026 ACC/AHA Dyslipidemia Guideline incorporates CKM syndrome (cardiovascular-kidney-metabolic syndrome) as an important clinical setting in which cholesterol-depleted LDL particles are common and ApoB discordance is especially relevant.

Risk Follows ApoB, Not LDL-C

Data from the Copenhagen General Population Study examined statin-treated patients and found that when ApoB and LDL-C were discordant, all-cause mortality risk followed ApoB. Patients with ApoB above the median but LDL-C below the median had increased risk, while patients with ApoB below the median — even with elevated LDL-C — did not show increased risk. Similar findings were observed for ApoB versus non-HDL-C discordance. This does not mean LDL-C is irrelevant, but rather that when LDL-C and ApoB disagree, ApoB is the more reliable indicator.

Mendelian randomisation analyses have confirmed this at the genetic level: when genetic variants produce discordant reductions in LDL-C and ApoB, the reduction in cardiovascular events tracks with the ApoB reduction, not the LDL-C reduction.

When Should ApoB Be Measured?

Based on the 2024 NLA Expert Clinical Consensus and the 2026 ACC/AHA Dyslipidemia Guideline, ApoB measurement adds clinical value in the following scenarios:

Adapted from: Soffer et al. J Clin Lipidol. 2024;18(5):e647–e663 and Blumenthal et al. Circulation. 2026;153:e00–e00.

ApoB Thresholds for Clinical Decision-Making

ApoB treatment targets are not yet as uniformly codified across guidelines as LDL-C targets. However, several useful thresholds have emerged from the 2024 NLA Expert Clinical Consensus and the 2026 ACC/AHA Guideline. These should be interpreted alongside LDL-C and non-HDL-C goals, not as replacements for them.

Sources: Soffer et al. J Clin Lipidol. 2024;18(5):e647–e663; Blumenthal et al. Circulation. 2026; Mach et al. Eur Heart J. 2020;41(1):111–188.

Evidence From Major Clinical Trials

While no randomised controlled trial has yet used ApoB as a primary treatment target, post hoc analyses from several landmark trials consistently demonstrate that ApoB is a strong predictor of cardiovascular events during treatment — often outperforming LDL-C.

ODYSSEY OUTCOMES (Alirocumab + Statin)

In over 18,000 patients with recent acute coronary syndrome, achieved ApoB remained predictive of MACE after adjustment for achieved LDL-C or non-HDL-C, suggesting that ApoB captures residual atherogenic particle risk not fully reflected by cholesterol targets alone. In contrast, achieved LDL-C and non-HDL-C were not individually predictive after adjustment for on-treatment ApoB.

FOURIER + IMPROVE-IT (Combined Analysis)

A combined analysis of evolocumab (FOURIER) and ezetimibe (IMPROVE-IT) data showed that achieved ApoB was the best predictor of myocardial infarction risk, remaining predictive even after adjustment for non-HDL-C and triglyceride concentrations.

TNT + IDEAL (Statin Monotherapy)

In combined data from these two statin trials, non-HDL-C and ApoB had the strongest relationships to MACE per standard deviation increase (HR 1.19 for both), compared with HR 1.15 for LDL-C. While confidence intervals overlapped, the consistent numerical superiority of ApoB and non-HDL-C supports their use alongside LDL-C for treatment monitoring.

ApoB and Lp(a): Understanding the Relationship

Lipoprotein(a), or Lp(a), is an LDL-like particle that carries one ApoB-100 molecule plus an additional apolipoprotein(a) strand. Because of this, Lp(a) particles are counted in the total ApoB measurement. In patients with elevated Lp(a), a portion of their measured total ApoB represents Lp(a)-associated particles that cannot be lowered by statins.

The Lp(a)-Corrected ApoB Calculator above provides an educational estimate of how much of total ApoB may be attributable to Lp(a) particles. This can help explain why a patient's ApoB appears higher than expected relative to their LDL-C, or why ApoB may not fall as much as anticipated with statin therapy.

For more information on Lp(a), see our comprehensive Lipoprotein(a) Review.

ApoB for Identifying Inherited Lipid Disorders

ApoB measurement, in combination with total cholesterol and triglycerides, can assist with lipoprotein phenotyping using the Fredrickson-Levy-Lees classification system. This helps clinicians characterise the underlying lipid disorder and identify inherited conditions:

Familial hypercholesterolaemia (FH): ApoB is often elevated in FH because LDL particle number is high, but ApoB alone is not diagnostic. Clinical criteria (such as the DLCN scoring system) and, when appropriate, genetic testing remain central to the diagnosis. The 2026 ACC/AHA guideline uses ApoB ≥140 mg/dL as a prompt for further evaluation in the setting of severe hypercholesterolaemia.

Familial combined hyperlipidaemia (FCH): elevated ApoB with variable elevations in LDL-C and/or triglycerides — the most common inherited lipid disorder, affecting approximately 1–2% of the population. ApoB is particularly helpful here because it captures the atherogenic burden even when LDL-C fluctuates.

Familial dysbetalipoproteinaemia (Type III): characterised by elevated triglycerides with a disproportionately low ApoB relative to cholesterol levels. ApoB is central to the diagnostic algorithm for this condition.

Identifying these conditions through ApoB-guided phenotyping enables targeted therapy and cascade screening of family members — potentially identifying at-risk individuals before they develop cardiovascular disease.

Practical Points About ApoB Testing

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