How should I order a serum apolipoprotein B test?

How to Order Apolipoprotein B (Apo-B) Levels

Order apolipoprotein B as an individually orderable test (not part of a standard lipid panel), either as an in-house or send-out test, and the sample does not require fasting. 1

Ordering Specifications

Test Ordering Details

• Order as a standalone test: Apo-B should be requested separately from the standard lipid panel (which includes total cholesterol, LDL-C, HDL-C, non-HDL-C, and triglycerides) 1
• Fasting not required: Apo-B levels are unaffected by fasting status and can be measured in both fasting and non-fasting states 2
• Laboratory availability: If your laboratory doesn't perform the test in-house, it should be available as a send-out test 1

When to Order Apo-B

The most recent Canadian guidelines 1 recommend offering Apo-B as an individually orderable test, particularly useful in specific clinical scenarios:

Primary indications for ordering:

• Patients with elevated triglycerides (≥200 mg/dL): Apo-B ≥130 mg/dL should be considered a risk-enhancing factor 3
• Metabolic syndrome or insulin resistance: Where LDL-C may underestimate atherogenic particle burden 2
• Discordance assessment: When you suspect LDL-C may not accurately reflect cardiovascular risk 2
• Monitoring lipid-lowering therapy adequacy: Apo-B appears to be a better index of treatment adequacy than LDL-C 4
• Familial hyperlipidemia differentiation: Helps distinguish between familial hypertriglyceridemia and familial combined hyperlipidemia 5

Clinical Context and Interpretation

Target Levels Based on Risk Category

For very high CV risk patients (established CVD, diabetes with target organ damage):

• Apo-B goal: <80 mg/dL 6

For high CV risk patients:

• Apo-B goal: <100 mg/dL 6, 4

Risk-enhancing threshold:

• Apo-B ≥130 mg/dL constitutes a risk-enhancing factor, corresponding roughly to LDL-C ≥160 mg/dL 3

Important Caveats

Standardization challenges: While Apo-B measurement offers technical advantages (good immunochemical methods, no fasting requirement, not sensitive to high triglycerides), there is ongoing work to establish reference measurement procedures and commutable reference materials 1. The IFCC Working Group is actively working to standardize measurements using mass spectrometry 1, 7.

Not universally recommended as primary target: Despite evidence suggesting Apo-B may outperform LDL-C in risk prediction, most guidelines still maintain LDL-C as the primary target because virtually all clinical trials used LDL-C endpoints 8. However, Apo-B serves as an excellent secondary marker and treatment target 6.

Complementary to standard lipids: Approximately 95% of patients who achieve LDL-C and non-HDL-C targets also achieve Apo-B targets 9, but the 5% who don't represent an important group with residual risk that would be missed without Apo-B measurement.

Practical Ordering Approach

1. Check laboratory capabilities: Confirm whether your lab performs Apo-B in-house or requires send-out
2. Order as separate test: Request "Apolipoprotein B" or "Apo-B" as an individual test code
3. No special preparation needed: Patient does not need to fast
4. Document clinical indication: Note reason for ordering (e.g., "elevated triglycerides," "risk assessment with metabolic syndrome," "treatment monitoring")
5. Ensure assay method is reported: The laboratory report should state which assay method was used 1

The measurement adds particular value when traditional lipid markers may be misleading, especially in patients with hypertriglyceridemia, metabolic syndrome, or when assessing adequacy of lipid-lowering therapy 2, 4.