ApoA1 + B + Ratio Lab Test Does NOT Check Lipoprotein(a) or Lipoprotein(b)
No, the Apolipoprotein A1 (ApoA1) + Apolipoprotein B (ApoB) ratio lab test does NOT measure lipoprotein(a) [Lp(a)] or lipoprotein(b)—these are completely different molecules that require separate testing.
What This Test Actually Measures
The ApoA1 + ApoB + ratio panel measures three distinct parameters 1:
- Apolipoprotein A1 (ApoA1): The major protein component of HDL ("good cholesterol") particles, providing an estimate of HDL particle concentration 1
- Apolipoprotein B (ApoB): The protein found in all atherogenic lipoproteins (LDL, VLDL, IDL), with each atherogenic particle containing exactly one ApoB molecule, making it a direct measure of total atherogenic particle number 2, 1
- ApoB/ApoA1 ratio: Represents the balance between atherogenic (bad) and protective (good) lipoproteins 2
Why Lipoprotein(a) Is Different
Lipoprotein(a) [Lp(a)] is a distinct lipoprotein particle that requires its own separate blood test 3, 4:
- Lp(a) consists of an LDL-like particle (which contains one ApoB molecule) attached to an additional unique protein called apolipoprotein(a) 5
- While Lp(a) does contain ApoB, standard ApoB measurements cannot distinguish between ApoB in regular LDL particles versus ApoB in Lp(a) particles 3
- Lp(a) must be specifically ordered as a separate test to identify patients with genetically elevated levels (target <50 mg/dL or <125 nmol/L) 3
- The European Society of Cardiology recommends measuring Lp(a) once in all high-risk patients, as levels are genetically determined and remain stable throughout life 3
Clinical Significance of the Distinction
This distinction matters because 3, 4:
- In patients with elevated Lp(a) (>30-50 mg/dL), standard ApoB measurements may underestimate total cardiovascular risk 3
- Lp(a) contributes to residual cardiovascular risk even when LDL-cholesterol and ApoB are well-controlled with statin therapy 4
- Elevated Lp(a) requires more aggressive ApoB lowering strategies, as event rates remain elevated at any achieved LDL-cholesterol level when Lp(a) is high 3
Practical Testing Recommendations
Based on current guidelines 1, 3:
- Order ApoA1 and ApoB testing for cardiovascular risk assessment, particularly in patients with metabolic syndrome, diabetes, chronic kidney disease, or when triglycerides are persistently ≥200 mg/dL 1, 3
- Separately order Lp(a) testing at least once in high-risk patients to identify those with genetically elevated levels 3
- ApoA1 and ApoB testing does not require fasting and can be collected at any time of day 1
- Lp(a) also does not require fasting and needs to be measured only once, as levels are genetically determined 3
Note on "Lipoprotein(b)"
There is no clinically relevant lipoprotein called "lipoprotein(b)"—you may be confusing this with either:
- Apolipoprotein B (ApoB): The protein measured in this test
- Lipoprotein(a) [Lp(a)]: The separate cardiovascular risk marker discussed above