Lipids: interpretation and disease correlation

16 ASCP MLS practice questions on Lipids: interpretation and disease correlation, part of Chemistry. The first 16 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

1. Question 1 · Hard

   A 61-year-old woman with type 2 diabetes and a previous myocardial infarction takes a high-intensity statin. Her clinic's target is an LDL cholesterol below 100 mg/dL [2.6 mmol/L], with the non-HDL cholesterol target set 30 mg/dL [0.8 mmol/L] above the LDL target. Her fasting results: total cholesterol 186 mg/dL [4.81 mmol/L], HDL cholesterol 32 mg/dL [0.83 mmol/L], triglyceride 330 mg/dL [3.73 mmol/L]. The laboratory calculates LDL cholesterol with the Friedewald equation. How do her results compare with the clinic's targets?

   1. ABoth LDL and non-HDL at target
   2. BLDL at target; non-HDL above target
   3. CLDL above target; non-HDL at target
   4. DBoth LDL and non-HDL above target

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   Answer: B · LDL at target; non-HDL above target

   The triglyceride is below 400 mg/dL, so the Friedewald equation is valid: LDL = 186 - 32 - (330/5) = 186 - 32 - 66 = 88 mg/dL [2.28 mmol/L], which meets the target of below 100 mg/dL. Non-HDL cholesterol = 186 - 32 = 154 mg/dL [3.98 mmol/L], above its target of 100 + 30 = 130 mg/dL. Non-HDL cholesterol includes the cholesterol in VLDL and remnant particles, which is high when triglyceride is raised, so it shows risk that the LDL figure misses. This is why non-HDL cholesterol is used as a secondary target when triglyceride is 200 mg/dL or more.

   • A: Non-HDL is 186 - 32 = 154 mg/dL, above its 130 mg/dL target.
   • C: This swaps the two results: LDL is 88 mg/dL and non-HDL 154 mg/dL.
   • D: LDL is 88 mg/dL once TG/5 (66) is subtracted; leaving out the VLDL term gives 154.

2. Question 2 · Hard

   A 58-year-old man has yellow-orange deposits in the creases of both palms and raised yellow nodules on his elbows. He takes no lipid-lowering drugs, and his TSH is normal. Fasting results: total cholesterol 356 mg/dL [9.21 mmol/L], triglyceride 380 mg/dL [4.29 mmol/L], HDL cholesterol 36 mg/dL [0.93 mmol/L], apolipoprotein B 96 mg/dL (reference 60-130 mg/dL). Beta-quantification by ultracentrifugation gives VLDL cholesterol 202 mg/dL [5.22 mmol/L] and LDL cholesterol 118 mg/dL [3.05 mmol/L]. Lipoprotein electrophoresis shows one broad band spanning the beta and pre-beta zones. The most likely diagnosis is:

   1. AFamilial dysbetalipoproteinemia
   2. BFamilial chylomicronemia syndrome
   3. CHeterozygous familial hypercholesterolemia
   4. DFamilial combined hyperlipidemia

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   Answer: A · Familial dysbetalipoproteinemia

   Cholesterol and triglyceride are raised to a similar degree, and palmar crease xanthomas are almost specific for familial dysbetalipoproteinemia (type III). The Friedewald LDL would be 356 - 36 - 76 = 244 mg/dL, but ultracentrifugation shows a true LDL of only 118 mg/dL, because the cholesterol sits in cholesterol-rich remnant particles. The VLDL cholesterol to triglyceride ratio is 202/380 = 0.53; a ratio above 0.3 supports type III, and the broad beta band is the classic electrophoresis finding. Apo B is not raised, because the remnants are fewer but larger particles. Most patients are homozygous for apo E2, and a second factor such as obesity, diabetes or hypothyroidism brings out the disorder.

   • B: Chylomicronemia gives triglyceride usually above 1,000 mg/dL with eruptive, not palmar, xanthomas.
   • C: Familial hypercholesterolemia has a high true LDL, tendon xanthomas and usually normal triglyceride.
   • D: Familial combined hyperlipidemia has a raised apo B and no palmar xanthomas.

3. Question 3 · Easy

   The risk of acute pancreatitis rises sharply when fasting triglyceride is above about:

   1. A200 mg/dL (2.3 mmol/L)
   2. B1,000 mg/dL (11.3 mmol/L)
   3. C400 mg/dL (4.5 mmol/L)
   4. D150 mg/dL (1.7 mmol/L)

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   Answer: B · 1,000 mg/dL (11.3 mmol/L)

   Triglycerides above about 1,000 mg/dL (11.3 mmol/L) usually mean that chylomicrons are present. These can trigger pancreatitis, probably through toxic free fatty acids released by lipase in the pancreas. At this level, lowering triglyceride takes priority over lowering LDL. Such samples also cause lipemic interference in many other tests.

   • A: 200 mg/dL is where the high triglyceride range begins, not a pancreatitis threshold.
   • C: 400 mg/dL is the limit for using the Friedewald equation.
   • D: 150 mg/dL is the upper limit of normal triglyceride.

4. Question 4 · Medium

   Non-HDL cholesterol is a useful risk marker when triglycerides are high, because it includes the cholesterol carried in:

   1. ALDL particles alone
   2. BChylomicrons alone
   3. CAll apo B-containing lipoproteins
   4. DLipoprotein(a) alone

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   Answer: C · All apo B-containing lipoproteins

   Non-HDL cholesterol is total cholesterol minus HDL cholesterol, so it includes the cholesterol in VLDL, IDL, remnants, LDL and Lp(a). All of these carry apo B and can cause atherosclerosis. When triglycerides are high, more cholesterol is carried in VLDL and remnants, and LDL alone underestimates risk. The non-HDL target is usually 30 mg/dL (0.8 mmol/L) above the LDL target.

   • A: LDL alone misses the cholesterol in VLDL and remnants.
   • B: Chylomicrons are only one of the apo B particles included.
   • D: Lp(a) is included but is only a small part of non-HDL cholesterol.

5. Question 5 · Medium

   Apart from a triglyceride above 400 mg/dL (4.5 mmol/L), the Friedewald LDL calculation is also unreliable in a patient with:

   1. AFamilial dysbetalipoproteinemia
   2. BIsolated low HDL cholesterol
   3. CWell-controlled type 2 diabetes
   4. DFamilial hypercholesterolemia

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   Answer: A · Familial dysbetalipoproteinemia

   The Friedewald equation assumes that VLDL cholesterol equals triglyceride/5 in mg/dL, which holds for normal VLDL. In familial dysbetalipoproteinemia the remnant particles are rich in cholesterol, so TG/5 underestimates VLDL cholesterol and the calculated LDL is falsely high. The equation also fails when chylomicrons are present. Beta-quantification or a direct LDL method is used instead.

   • B: A low HDL is measured directly and does not affect the TG/5 assumption.
   • C: Well-controlled diabetes with normal triglyceride does not invalidate the equation.
   • D: In familial hypercholesterolemia, VLDL is usually normal, so the equation works.

6. Question 6 · Hard

   A fasting sample gives total cholesterol 245 mg/dL (6.34 mmol/L), HDL cholesterol 45 mg/dL (1.16 mmol/L) and triglyceride 480 mg/dL (5.42 mmol/L). Which calculated value is valid to report?

   1. AFriedewald LDL, 104 mg/dL
   2. BNon-HDL cholesterol, 200 mg/dL
   3. CFriedewald LDL, 200 mg/dL
   4. DNon-HDL cholesterol, 104 mg/dL

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7. Question 7 · Hard

   A 48-year-old man's fasting results are total cholesterol 260 mg/dL (6.72 mmol/L), HDL cholesterol 38 mg/dL (0.98 mmol/L) and triglyceride 210 mg/dL (2.37 mmol/L). Using the Friedewald equation, his LDL cholesterol is:

   1. A222 mg/dL
   2. B180 mg/dL
   3. C127 mg/dL
   4. D218 mg/dL

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8. Question 8 · Medium

   After overnight storage at 4 °C, a fasting plasma shows a creamy layer on top of a turbid lower layer. Which lipoprotein excess does this indicate?

   1. AChylomicrons and VLDL
   2. BLDL only
   3. CVLDL only
   4. DChylomicrons only

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9. Question 9 · Medium

   A 34-year-old man has xanthomas on both Achilles tendons. Fasting LDL cholesterol is 265 mg/dL (6.85 mmol/L), triglyceride 120 mg/dL (1.35 mmol/L), and his father had a myocardial infarction at 45. Which defect is most likely?

   1. ALipoprotein lipase deficiency
   2. BLDL receptor defect
   3. CApo E2 homozygosity
   4. DABCA1 transporter defect

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10. Question 10 · Hard

    Three members of one family are tested. One has raised LDL only, one raised triglyceride only, and one both; all three have raised apo B, and none has tendon xanthomas. The most likely diagnosis is:

    1. AFamilial combined hyperlipidemia
    2. BFamilial dysbetalipoproteinemia
    3. CFamilial chylomicronemia
    4. DFamilial hypercholesterolemia

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11. Question 11 · Medium

    Which lipid pattern is typical of insulin resistance and the metabolic syndrome?

    1. AChylomicrons with very low LDL
    2. BVery high LDL with normal TG
    3. CHigh TG, low HDL, small dense LDL
    4. DLow TG, high HDL, large buoyant LDL

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12. Question 12 · Hard

    A 2-year-old has fatty diarrhea, poor growth and acanthocytes on the blood smear. Total cholesterol is 38 mg/dL (0.98 mmol/L), triglyceride 8 mg/dL (0.09 mmol/L), and apo B is undetectable. Which protein is most likely defective?

    1. ACholesteryl ester transfer protein
    2. BLipoprotein lipase
    3. CMicrosomal triglyceride transfer protein
    4. DLecithin-cholesterol acyltransferase

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13. Question 13 · Medium

    A 52-year-old woman's LDL cholesterol has risen to 195 mg/dL (5.04 mmol/L) from 120 mg/dL (3.10 mmol/L) two years ago, with no change in diet. Which disorder is a common secondary cause that should be excluded?

    1. AHyperthyroidism
    2. BIntestinal malabsorption
    3. CAdvanced cirrhosis
    4. DHypothyroidism

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14. Question 14 · Easy

    Under NCEP ATP III cut points, an HDL cholesterol below which value is classed as low and counted as a risk factor?

    1. A60 mg/dL (1.6 mmol/L)
    2. B100 mg/dL (2.6 mmol/L)
    3. C40 mg/dL (1.0 mmol/L)
    4. D130 mg/dL (3.4 mmol/L)

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15. Question 15 · Hard

    A 25-year-old has enlarged orange-yellow tonsils, an enlarged spleen and peripheral neuropathy. HDL cholesterol is 3 mg/dL (0.08 mmol/L) and total cholesterol is low. Which defect is most likely?

    1. ALCAT defect
    2. BABCA1 defect
    3. CCETP defect
    4. DApo C-II defect

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16. Question 16 · Hard

    Total cholesterol 220 mg/dL, HDL 50 mg/dL and triglycerides 150 mg/dL. What is the LDL cholesterol by the Friedewald equation?

    1. A140 mg/dL
    2. B110 mg/dL
    3. C170 mg/dL
    4. D120 mg/dL

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