Lipid Profile Interpretation
On this page
Direct answer
A standard lipid panel reports total cholesterol, HDL cholesterol, triglycerides and a calculated LDL cholesterol, most often by the Friedewald equation — LDL equals total cholesterol minus HDL minus triglycerides divided by five in mg/dL — an estimate that fails when triglycerides exceed 400 mg/dL, in which case direct LDL or non-HDL must carry the interpretation. Non-HDL cholesterol (total minus HDL), representing all atherogenic particles, is valid fasting or fed, and its goal is simply the LDL goal plus 30 mg/dL. Indian lipid profiles skew toward high triglycerides and low HDL (atherogenic dyslipidaemia of the metabolic syndrome), so the LDL-centric report hides risk that non-HDL and apolipoprotein B expose.
What you must remember
- Desirable ranges (adults, mg/dL): total cholesterol below 200, LDL below 100 (below 70 in established coronary disease or diabetes), HDL above 40 in men and 50 in women, triglycerides below 150; triglycerides of 500 or more signal pancreatitis risk and shift priority to fibrates first.
- Friedewald formula: LDL = TC − HDL − TG/5; invalid when TG > 400 mg/dL, in type III hyperlipoproteinaemia, or on non-fasting samples with high TG — use direct LDL-C or the non-HDL value instead.
- Non-HDL cholesterol = TC − HDL; goal = LDL goal + 30 mg/dL (e.g. < 100 mg/dL when the LDL goal is 70); it captures VLDL, IDL and Lp(a) cholesterol as well.
- Secondary causes to exclude before labelling any dyslipidaemia primary: hypothyroidism (check TSH — the commonest reversible cause in Indian clinics), diabetes, nephrotic syndrome, chronic kidney disease, obstructive liver disease, alcohol, thiazides, beta blockers, steroids, antiretrovirals.
- Indian phenotype: the atherogenic triad of high triglycerides, low HDL and small dense LDL predominates; LDL may look deceptively modest while non-HDL and apo B are high — a reason guidelines for South Asians recommend treating at lower LDL thresholds.
- Sample conditions: a 9-12 hour fast was traditional; non-fasting sampling is now acceptable for most purposes except known hypertriglyceridaemia, where fasting values guide fibrate therapy.
- Remnant cholesterol (approximately non-HDL minus LDL) is emerging as an inflammatory, atherogenic fraction — worth one line in a good answer.
Reading one report line by line
Consider a 45-year-old Sikh businessman with a family history of early MI: TC 232, HDL 34, TG 320 mg/dL. Friedewald gives LDL = 232 − 34 − 64 = 134 mg/dL, apparently only borderline. But two corrections follow. First, with TG at 320, the formula's TG/5 term is least reliable, so cross-check with non-HDL = 232 − 34 = 198 mg/dL — nearly double any reasonable goal of 100 for a high-risk South Asian. Second, request apo B: at this triglyceride level, particle number is likely high from small dense LDL and remnants. Now the plan becomes biochemically honest: rule out secondary causes with TSH, HbA1c, creatinine, urine protein; treat with a moderate- or high-intensity statin plus attention to refined carbohydrate and alcohol (both raise TG in Indians disproportionately); add fenofibrate only if TG stays above about 500 mg/dL for pancreatitis prevention, since fibrate-outcome data in combination therapy are neutral outside severe hypertriglyceridaemia. The teaching point is procedural: never read the LDL line alone — read the triglyceride line first, because it decides whether the LDL line can be trusted.
How the examiner frames it
Three recurring demands. One: "Why is non-HDL better than LDL in this report?" — because it includes every apo B particle's cholesterol and survives high TG. Two: "Patient non-fasting, does it invalidate?" — no for TC, HDL, non-HDL; TG rises modestly after food, so recheck fasting if TG is elevated. Three: the numerical trap of the Friedewald formula in SI units — divide triglycerides by 2.2, not 5, when everything is in mmol/L; Indian laboratories report both units, and candidates routinely mix them.
Frequently asked questions
When does the Friedewald formula fail?
When triglycerides exceed 400 mg/dL, in type III dysbetalipoproteinaemia, and with markedly non-fasting samples; use direct LDL or non-HDL instead.
How is non-HDL cholesterol calculated and what is its goal?
Total cholesterol minus HDL cholesterol, with a target of LDL goal plus 30 mg/dL; it needs no fasting sample.
Which secondary cause of dyslipidaemia must be excluded first?
Hypothyroidism, by a TSH assay, since it elevates LDL through reduced receptor clearance and is fully reversible with levothyroxine.
Why do Indian lipid profiles need tighter interpretation?
South Asian dyslipidaemia features high triglycerides, low HDL and small dense LDL, so risk persists at modest LDL levels and non-HDL or apo B uncovers it.
What triglyceride level changes management priority?
Above about 500 mg/dL, pancreatitis risk dominates and triglyceride lowering (fibrate, omega-3 fatty acids, strict diet, alcohol cessation) takes precedence over LDL.