A 48-year-old woman has a lipid profile at a non-fasting workplace screening, drawn 2 hours after a large lunch: total cholesterol 5.6 mmol/L (217 mg/dL), HDL cholesterol 1.3 mmol/L (50 mg/dL), triglyceride 3.3 mmol/L (292 mg/dL), calculated LDL cholesterol 2.8 mmol/L (108 mg/dL). One week later, after a 12-hour fast, her results are total cholesterol 5.6 mmol/L, HDL cholesterol 1.3 mmol/L and triglyceride 1.3 mmol/L (115 mg/dL). The laboratory calculates LDL cholesterol with the Friedewald equation in mmol/L: LDL = total cholesterol - HDL - (triglyceride ÷ 2.2). What is her fasting LDL cholesterol, and why does it differ from the first result?

3.7 mmol/L; meal triglyceride inflated the VLDL term

4.0 mmol/L; meal triglyceride inflated the VLDL term

3.7 mmol/L; HDL cholesterol falls after a fatty meal

4.3 mmol/L; Friedewald cannot be used after a meal

A man is admitted with an acute myocardial infarction. When should his lipid profile be drawn so that it reflects his usual levels?

Within 24 hours of symptom onset

At 2 to 3 weeks after the event

On day 3 to 5, once he is stable

At 7 to 10 days, before discharge

Why can non-HDL cholesterol be reported reliably from a non-fasting sample?

Total and HDL cholesterol change little after a meal

Chylomicrons contain no cholesterol at all

HDL rises after a meal and offsets the triglyceride

The calculation corrects for the triglyceride rise

Lipid testing guidance asks that the patient sit for about 5 minutes before venipuncture. What is the reason?

Posture shifts plasma water and alters lipid levels

Sitting lowers triglyceride left from the last meal

Rest stops exercise-driven release of chylomicrons

Standing releases extra HDL from tissue stores

A 58-year-old with type 2 diabetes and a previous myocardial infarction has fasting results: total cholesterol 4.4 mmol/L (170 mg/dL), HDL cholesterol 0.9 mmol/L (35 mg/dL), triglyceride 4.0 mmol/L (354 mg/dL). His targets are LDL cholesterol below 1.8 mmol/L (70 mg/dL) and non-HDL cholesterol below 2.6 mmol/L (100 mg/dL). Using the Friedewald LDL, how do his results compare with the targets?

LDL at target, non-HDL above target

LDL and non-HDL both above target

LDL above target, non-HDL at target

Lipid testing and calculated LDL

14 DOH Abu Dhabi (HAAD) lab licensing practice questions on Lipid testing and calculated LDL, part of Clinical Chemistry. The first 14 are below; the first 5 with answers and explanations (tap Show answer after you have chosen), the rest in Learn with a free account.

Question 1 · Hard
A 48-year-old woman has a lipid profile at a non-fasting workplace screening, drawn 2 hours after a large lunch: total cholesterol 5.6 mmol/L (217 mg/dL), HDL cholesterol 1.3 mmol/L (50 mg/dL), triglyceride 3.3 mmol/L (292 mg/dL), calculated LDL cholesterol 2.8 mmol/L (108 mg/dL). One week later, after a 12-hour fast, her results are total cholesterol 5.6 mmol/L, HDL cholesterol 1.3 mmol/L and triglyceride 1.3 mmol/L (115 mg/dL). The laboratory calculates LDL cholesterol with the Friedewald equation in mmol/L: LDL = total cholesterol - HDL - (triglyceride ÷ 2.2). What is her fasting LDL cholesterol, and why does it differ from the first result?
1. A4.0 mmol/L; meal triglyceride inflated the VLDL term
2. B3.7 mmol/L; meal triglyceride inflated the VLDL term
3. C3.7 mmol/L; HDL cholesterol falls after a fatty meal
4. D4.3 mmol/L; Friedewald cannot be used after a meal
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Answer: B · 3.7 mmol/L; meal triglyceride inflated the VLDL term
Fasting LDL = 5.6 - 1.3 - (1.3 ÷ 2.2) = 5.6 - 1.3 - 0.59 = 3.7 mmol/L (143 mg/dL). Total and HDL cholesterol were the same on both days, so the whole difference comes from the triglyceride term. After a meal, chylomicrons and their remnants raise triglyceride but carry little cholesterol, so triglyceride ÷ 2.2 overestimates VLDL cholesterol and the non-fasting Friedewald LDL comes out too low (2.8 mmol/L). Dividing triglyceride by 5, the mg/dL factor, gives 4.0 mmol/L, and leaving the triglyceride term out gives the non-HDL cholesterol of 4.3 mmol/L. Non-fasting profiles are acceptable for screening, but when triglyceride is raised, a fasting repeat, a direct LDL or non-HDL cholesterol gives a truer picture.
- A: 4.0 mmol/L comes from dividing triglyceride by 5, the factor for mg/dL.
- C: Her HDL cholesterol is 1.3 mmol/L on both days, so it did not change.
- D: 4.3 mmol/L is total minus HDL cholesterol, which is non-HDL cholesterol, not LDL.
Question 2 · Medium
A man is admitted with an acute myocardial infarction. When should his lipid profile be drawn so that it reflects his usual levels?
1. AAt 2 to 3 weeks after the event
2. BWithin 24 hours of symptom onset
3. COn day 3 to 5, once he is stable
4. DAt 7 to 10 days, before discharge
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Answer: B · Within 24 hours of symptom onset
After a myocardial infarction, the acute-phase response lowers total, LDL and HDL cholesterol, starting about 24 to 48 hours after onset. Levels can stay depressed for 6 to 8 weeks, so a sample in that window underestimates the patient's usual lipids. A sample drawn in the first 24 hours reflects the baseline well; otherwise the profile is repeated after recovery. Surgery, infection and other acute illness have a similar effect.
- A: At 2 to 3 weeks, lipids have usually not returned to baseline.
- C: By day 3 to 5, cholesterol has already fallen with the acute-phase response.
- D: At 7 to 10 days, lipids are still depressed.
Question 3 · Medium
Why can non-HDL cholesterol be reported reliably from a non-fasting sample?
1. AChylomicrons contain no cholesterol at all
2. BTotal and HDL cholesterol change little after a meal
3. CHDL rises after a meal and offsets the triglyceride
4. DThe calculation corrects for the triglyceride rise
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Answer: B · Total and HDL cholesterol change little after a meal
After a usual meal, triglyceride rises by roughly 0.3 mmol/L (26 mg/dL), while total and HDL cholesterol change by only about 0.2 mmol/L or less. Non-HDL cholesterol is total cholesterol minus HDL cholesterol and uses no triglyceride, so it is barely affected by eating. It also counts the cholesterol in remnant particles, which adds to risk after meals. For this reason the EAS/EFLM consensus accepts non-fasting samples for routine lipid profiles.
- A: Chylomicrons carry some cholesterol, though mostly triglyceride.
- C: HDL does not rise meaningfully after a meal.
- D: Non-HDL cholesterol uses no triglyceride, so there is nothing to correct.
Question 4 · Medium
Lipid testing guidance asks that the patient sit for about 5 minutes before venipuncture. What is the reason?
1. APosture shifts plasma water and alters lipid levels
2. BSitting lowers triglyceride left from the last meal
3. CRest stops exercise-driven release of chylomicrons
4. DStanding releases extra HDL from tissue stores
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Answer: A · Posture shifts plasma water and alters lipid levels
When a person stands, water moves from the blood into the tissues, so lipoproteins and other large molecules become more concentrated; total cholesterol can be about 10% higher standing than lying down. Seating the patient for a standard time, and keeping the tourniquet on for less than a minute, makes results comparable between visits. This matters because treatment decisions rest on fixed cut-offs and small changes. The same posture effect applies to proteins and protein-bound analytes such as calcium.
- B: Five minutes of sitting does not change post-meal triglyceride.
- C: Chylomicrons come from dietary fat, not from exercise.
- D: HDL is not released from tissues on standing; it is concentrated with the other lipoproteins.
Question 5 · Hard
A 58-year-old with type 2 diabetes and a previous myocardial infarction has fasting results: total cholesterol 4.4 mmol/L (170 mg/dL), HDL cholesterol 0.9 mmol/L (35 mg/dL), triglyceride 4.0 mmol/L (354 mg/dL). His targets are LDL cholesterol below 1.8 mmol/L (70 mg/dL) and non-HDL cholesterol below 2.6 mmol/L (100 mg/dL). Using the Friedewald LDL, how do his results compare with the targets?
1. ALDL at target, non-HDL above target
2. BLDL and non-HDL both above target
3. CLDL and non-HDL both at target
4. DLDL above target, non-HDL at target
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Answer: A · LDL at target, non-HDL above target
VLDL cholesterol = 4.0 ÷ 2.2 = 1.8 mmol/L, so LDL = 4.4 − 0.9 − 1.8 = 1.7 mmol/L (65 mg/dL), just below target. Non-HDL cholesterol = 4.4 − 0.9 = 3.5 mmol/L (135 mg/dL), well above its target. The gap is the cholesterol in triglyceride-rich remnants, which LDL alone ignores, and Friedewald also tends to underestimate LDL at this triglyceride. In hypertriglyceridemia, non-HDL cholesterol or apo B better reflects the remaining risk.
- B: The LDL of 1.7 mmol/L is below its 1.8 mmol/L target.
- C: Non-HDL cholesterol of 3.5 mmol/L is well above its 2.6 mmol/L target.
- D: This reverses the results: LDL is at target and non-HDL is not.
Question 6 · Medium
In beta-quantification, the reference method for LDL cholesterol, ultracentrifugation of plasma at a density of 1.006 g/mL is used to:
1. AFloat off VLDL and chylomicrons
2. BRemove all apo B-containing particles
3. CSediment HDL from the plasma
4. DSeparate lipoprotein(a) from LDL
Answer and explanation in LearnFree account
Question 7 · Medium
Compared with Friedewald, the Martin-Hopkins equation is more accurate at high triglyceride and low LDL mainly because it:
1. ARequires an ultracentrifuged sample first
2. BUses a variable triglyceride-to-VLDL cholesterol factor
3. CMeasures VLDL cholesterol directly by precipitation
4. DAdds apolipoprotein B to the calculation
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Question 8 · Hard
In a precipitation method for HDL cholesterol, a sample with triglyceride 7.5 mmol/L (664 mg/dL) still has a cloudy supernatant after centrifugation. The reported HDL cholesterol will be:
1. AAccurate, as only HDL remains in solution
2. BFalsely low, as lipid inhibits the enzymes
3. CFalsely high, from VLDL left in the supernatant
4. DFalsely low, from HDL lost in the precipitate
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Question 9 · Hard
A fasting sample gives total cholesterol 6.4 mmol/L (247 mg/dL), HDL cholesterol 1.2 mmol/L (46 mg/dL) and triglyceride 2.2 mmol/L (195 mg/dL). The Friedewald LDL cholesterol is:
1. A3.0 mmol/L (116 mg/dL)
2. B4.8 mmol/L (186 mg/dL)
3. C4.2 mmol/L (162 mg/dL)
4. D5.2 mmol/L (201 mg/dL)
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Question 10 · Easy
Homogeneous direct LDL cholesterol assays run on automated analyzers with no separation step. They achieve this by:
1. AMasking or clearing non-LDL lipoproteins with detergents
2. BMeasuring apolipoprotein B by immunoturbidimetry
3. CCalculating LDL from total cholesterol, HDL and triglyceride
4. DPrecipitating LDL and measuring the supernatant
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Question 11 · Hard
A 50-year-old woman on a high-dose statin has fasting results: total cholesterol 3.6 mmol/L (139 mg/dL), HDL cholesterol 0.8 mmol/L (31 mg/dL), triglyceride 3.9 mmol/L (345 mg/dL). The Friedewald LDL is 1.0 mmol/L (39 mg/dL), but a direct LDL method gives 1.5 mmol/L (58 mg/dL). What best explains the difference?
1. AFriedewald overestimates VLDL cholesterol at high triglyceride
2. BFriedewald overestimates LDL when HDL is low
3. CDirect LDL methods also measure HDL cholesterol
4. DStatins interfere with homogeneous direct LDL assays
Answer and explanation in LearnFree account
Question 12 · Hard
After a new LIS calculation goes live, a fasting profile reads total cholesterol 6.0 mmol/L, HDL cholesterol 1.0 mmol/L, triglyceride 2.0 mmol/L and calculated LDL 4.6 mmol/L. Which setup error explains the LDL?
1. AHDL cholesterol not subtracted
2. BWhole triglyceride subtracted
3. CTriglyceride divided by 5 instead of 2.2
4. DTriglyceride term left out
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Question 13 · Medium
Using the Friedewald equation in mmol/L, LDL = total cholesterol − HDL − (triglyceride ÷ 2.2), what LDL cholesterol should be reported for Patient B in the table shown?
Figure: MedExams
1. A4.8 mmol/L
2. B3.9 mmol/L
3. C5.2 mmol/L
4. D4.4 mmol/L
Answer and explanation in LearnFree account
Question 14 · Easy
Which lipid result is most affected by a recent meal?
1. ATriglycerides
2. BApolipoprotein A1
3. CTotal cholesterol
4. DHDL cholesterol
Answer and explanation in LearnFree account

Lipid testing and calculated LDL

A man is admitted with an acute myocardial infarction. When should his lipid profile be drawn so that it reflects his usual levels?

Why can non-HDL cholesterol be reported reliably from a non-fasting sample?

Lipid testing guidance asks that the patient sit for about 5 minutes before venipuncture. What is the reason?

In beta-quantification, the reference method for LDL cholesterol, ultracentrifugation of plasma at a density of 1.006 g/mL is used to:

Compared with Friedewald, the Martin-Hopkins equation is more accurate at high triglyceride and low LDL mainly because it:

In a precipitation method for HDL cholesterol, a sample with triglyceride 7.5 mmol/L (664 mg/dL) still has a cloudy supernatant after centrifugation. The reported HDL cholesterol will be:

A fasting sample gives total cholesterol 6.4 mmol/L (247 mg/dL), HDL cholesterol 1.2 mmol/L (46 mg/dL) and triglyceride 2.2 mmol/L (195 mg/dL). The Friedewald LDL cholesterol is:

Homogeneous direct LDL cholesterol assays run on automated analyzers with no separation step. They achieve this by:

After a new LIS calculation goes live, a fasting profile reads total cholesterol 6.0 mmol/L, HDL cholesterol 1.0 mmol/L, triglyceride 2.0 mmol/L and calculated LDL 4.6 mmol/L. Which setup error explains the LDL?

Using the Friedewald equation in mmol/L, LDL = total cholesterol − HDL − (triglyceride ÷ 2.2), what LDL cholesterol should be reported for Patient B in the table shown?

Which lipid result is most affected by a recent meal?