Lipid Panel: Beyond Total Cholesterol—Non-HDL, ApoB, Lp(a), and Secondary Causes

LDL-C is calculated, not measured. Non-HDL may be better. And nobody's checking Lp(a) yet even though they should be.

The lipid panel is ordered on nearly every adult in primary care, yet most providers look at the LDL-C, compare it to a target, and stop. The panel actually contains much more information—and the advanced markers that are increasingly recommended (non-HDL, apoB, Lp(a)) are the ones that predict cardiovascular events better than LDL alone.

The Standard Panel

• Total cholesterol: LDL + HDL + VLDL. Largely supplanted by its components for clinical decisions.
• LDL-C: Usually calculated by the Friedewald equation (TC − HDL − TG/5). Inaccurate when triglycerides >400 (equation breaks down) or when LDL is very low. Direct LDL measurement is available but not standard.
• HDL-C: Higher is generally protective. Very low HDL (<40 men, <50 women) increases cardiovascular risk. Pharmacologically raising HDL has NOT been shown to reduce events.
• Triglycerides: Fasting preferred for accuracy but non-fasting is acceptable for screening. >500 mg/dL = pancreatitis risk requiring treatment regardless of cardiovascular risk.
• Non-HDL cholesterol = Total cholesterol − HDL. Captures ALL atherogenic lipoproteins (LDL + VLDL + IDL + Lp(a)). Better predictor of cardiovascular risk than LDL-C alone, especially in patients with elevated triglycerides where calculated LDL is unreliable. Target: typically LDL goal + 30.

Advanced Markers: When to Go Beyond the Standard Panel

ApoB (Apolipoprotein B)

Each atherogenic lipoprotein particle (LDL, VLDL, IDL, Lp(a)) contains exactly one apoB molecule. ApoB therefore counts the total number of atherogenic particles, making it the single best measure of atherogenic burden. It's superior to LDL-C in patients with metabolic syndrome, diabetes, obesity, or high triglycerides where LDL-C may underestimate risk (discordance between particle number and cholesterol content). Consider ordering when LDL-C is at goal but the patient has metabolic syndrome or premature ASCVD.

Lp(a) (Lipoprotein(a))

The most underordered cardiovascular risk marker in medicine. Lp(a) is a genetically determined, highly atherogenic lipoprotein that is NOT lowered by statins, diet, or exercise. Elevated Lp(a) (>50 mg/dL or >125 nmol/L) independently increases ASCVD risk 2–3 fold and aortic stenosis risk. Current guidelines (2024 ESC, AHA/ACC consideration) recommend checking Lp(a) at least once in every adult's lifetime since it's genetically fixed. If elevated, it changes risk stratification (may warrant more aggressive LDL lowering) and will have targeted therapies (antisense oligonucleotides) entering the market.

When to Order Lp(a)

Check at least once in all adults. Especially important in: premature ASCVD (men <55, women <65), family history of premature ASCVD, recurrent events despite optimal statin therapy, borderline risk where Lp(a) could change the treatment decision, and calcific aortic stenosis.

Fasting vs. Non-Fasting

Current guidelines (2018 AHA/ACC, 2024 ESC) accept non-fasting lipid panels for initial screening. Triglycerides are the main value affected by fasting (can rise 20–30% postprandially). A fasting panel is needed when: triglycerides are >400 on non-fasting, you need accurate calculated LDL-C, or you're monitoring response to triglyceride-lowering therapy.

Secondary Causes of Dyslipidemia

Before attributing dyslipidemia to "genetics" or "diet," rule out secondary causes:

Lipid Abnormality	Secondary Causes to Consider
Elevated LDL	Hypothyroidism (check TSH!), nephrotic syndrome, obstructive liver disease, anorexia, medications (thiazides, cyclosporine, retinoids)
Elevated triglycerides	Uncontrolled diabetes/insulin resistance, alcohol, obesity, CKD, medications (steroids, beta-blockers, estrogen, retinoids, atypical antipsychotics, protease inhibitors)
Low HDL	Metabolic syndrome, smoking, sedentary lifestyle, anabolic steroids, beta-blockers, progestins
Severely elevated TG (>500)	Familial hypertriglyceridemia, uncontrolled diabetes, alcohol, medications, pregnancy

Don't Miss Hypothyroidism

Hypothyroidism is one of the most common reversible causes of elevated LDL. Always check TSH before starting a statin for new dyslipidemia. Correcting the thyroid may normalize the lipids without medication.

Pediatric Lipid Screening

• Universal screening: Non-fasting lipid panel once between ages 9–11 and again at 17–21 (NHLBI guidelines).
• Targeted screening: Children ≥2 years with family history of premature ASCVD, dyslipidemia, or risk factors (obesity, diabetes, hypertension).
• Familial hypercholesterolemia should be suspected when LDL >160 in a child or >190 in an adult. Cascade screening of family members is indicated.

Bottom Line

The lipid panel is more than LDL-C. Non-HDL is free (calculate from the standard panel) and better than LDL-C in metabolic syndrome. ApoB counts atherogenic particles directly. Lp(a) should be checked once in every adult. Always rule out secondary causes before starting a statin. And check that TSH.

Stay sharp out there.