CLS Lipid Panel Interpretation 2 — Questions and Answers
Question 1: A patient's lipid panel shows LDL-C 160 mg/dL, HDL-C 38 mg/dL, TG 280 mg/dL, and total cholesterol 254 mg/dL. The Friedewald equation was used. Why might the calculated LDL-C be unreliable?
- HDL-C is below 40 mg/dL in men
- Triglycerides exceed 200 mg/dL, reducing accuracy (Correct answer)
- Total cholesterol is above 240 mg/dL
- The patient was not fasting for 12 hours
Correct answer: Triglycerides exceed 200 mg/dL, reducing accuracy
The Friedewald equation becomes unreliable when triglycerides exceed 200 mg/dL and is invalid above 400 mg/dL because VLDL-C estimation (TG/5) is inaccurate at elevated TG levels.
Question 2: Which lipoprotein fraction is most directly measured in a standard fasting lipid panel rather than calculated?
- LDL cholesterol
- VLDL cholesterol
- HDL cholesterol (Correct answer)
- Non-HDL cholesterol
Correct answer: HDL cholesterol
HDL cholesterol is directly measured via precipitation or homogeneous assay methods, whereas LDL-C and VLDL-C are typically calculated from measured values.
Question 3: A non-fasting lipid panel is acceptable for initial cardiovascular risk screening primarily because which value is least affected by a recent meal?
- Triglycerides
- LDL-C by Friedewald equation
- HDL-C (Correct answer)
- VLDL-C
Correct answer: HDL-C
HDL-C remains relatively stable after meals and is the least postprandially affected major lipid fraction, making non-fasting panels useful for initial screening.
Question 4: A patient has TG of 650 mg/dL. Which parameter on the lipid panel can still be reliably used to guide statin therapy initiation?
- Calculated LDL-C
- Non-HDL cholesterol (Correct answer)
- VLDL cholesterol
- LDL particle number by NMR
Correct answer: Non-HDL cholesterol
Non-HDL cholesterol (total cholesterol minus HDL-C) is directly calculated from measured values and remains valid regardless of triglyceride levels, making it the preferred treatment target when TG exceed 400 mg/dL.
Question 5: In a patient with familial hypercholesterolemia, which lipid panel finding is most characteristic?
- Markedly elevated triglycerides with normal LDL-C
- Severely elevated LDL-C with relatively normal triglycerides and HDL-C (Correct answer)
- Low HDL-C with elevated VLDL-C
- Elevated Lp(a) with normal LDL-C and HDL-C
Correct answer: Severely elevated LDL-C with relatively normal triglycerides and HDL-C
Familial hypercholesterolemia is characterized by dramatically elevated LDL-C (often >190 mg/dL in adults) due to defective LDL receptor function, with triglycerides and HDL-C typically in the normal range.
Question 6: A lipid panel shows TC 180 mg/dL, HDL-C 55 mg/dL, TG 90 mg/dL, and LDL-C 107 mg/dL. What is the calculated non-HDL cholesterol?
- 107 mg/dL
- 125 mg/dL (Correct answer)
- 90 mg/dL
- 143 mg/dL
Correct answer: 125 mg/dL
Non-HDL cholesterol = Total cholesterol − HDL-C = 180 − 55 = 125 mg/dL, encompassing all atherogenic lipoproteins including LDL, VLDL, IDL, and Lp(a).
Question 7: Which lipid panel result pattern is most consistent with type III hyperlipoproteinemia (familial dysbetalipoproteinemia)?
- Isolated LDL-C elevation >190 mg/dL
- Near-equal elevations of both cholesterol and triglycerides with elevated remnant lipoproteins (Correct answer)
- Severely elevated TG >1000 mg/dL with normal LDL-C
- Isolated low HDL-C <40 mg/dL with normal LDL and TG
Correct answer: Near-equal elevations of both cholesterol and triglycerides with elevated remnant lipoproteins
Type III hyperlipoproteinemia (apoE2/E2 genotype) is characterized by roughly equal elevations of cholesterol and triglycerides (both often 250–500 mg/dL) due to accumulation of IDL and chylomicron remnants.
CLS Lipid Panel Interpretation 2
A patient's lipid panel shows LDL-C 160 mg/dL, HDL-C 38 mg/dL, TG 280 mg/dL, and total cholesterol 254 mg/dL.
The Friedewald equation was used.
Why might the calculated LDL-C be unreliable?