Can a Person Have Both Apolipoprotein A and Apolipoprotein B?
Yes, every person normally has both apolipoprotein A (apo A) and apolipoprotein B (apo B) in their circulation—these are distinct proteins found on different lipoprotein particles that serve opposite physiological roles. 1
Normal Physiology of Apolipoproteins
Apo A1 is the major protein component of HDL (high-density lipoprotein), the "protective" cholesterol particles that transport cholesterol away from arteries back to the liver. 1, 2
Apo B is the major protein found on all atherogenic (artery-damaging) lipoproteins, including VLDL, IDL, and LDL particles, with each atherogenic particle containing exactly one apo B molecule. 1, 3
These two apolipoproteins represent opposing forces in cardiovascular health: apo B reflects the total burden of atherogenic particles, while apo A1 reflects the protective HDL system. 2
Clinical Significance of Having Both
The apo B/apo A1 ratio represents the balance between atherogenic and protective lipoproteins and has been used in large prospective studies as an indicator of cardiovascular risk. 1, 2
Normal reference ranges exist for both: apo A1 levels <120 mg/dL for men and <140 mg/dL for women are considered low, while apo B levels ≥130 mg/dL constitute a cardiovascular risk-enhancing factor. 1, 4
Disorders Affecting Both Apolipoproteins
Familial combined hyperlipidemia (FCHL) is a common genetic disorder (1-2% of white populations) characterized by increased production of apo B lipoproteins, which can occur alongside abnormal apo A1 levels. 1
Patients with premature coronary artery disease frequently have both decreased apo A1 and increased apo B levels simultaneously, with stepwise discriminant analysis showing that decreased apo A1 and increased apo B are both significant independent factors distinguishing patients with coronary disease from controls. 5
Rare genetic conditions like abetalipoproteinemia result in absent apo B-containing lipoproteins (undetectable LDL-C), but these patients still produce apo A1 and HDL particles. 1
Clinical Assessment Approach
When evaluating cardiovascular risk, both apo A1 and apo B provide complementary information, though current treatment strategies prioritize lowering apo B rather than raising apo A1, as the evidence base for apo B reduction is substantially stronger. 2, 4
The primary therapeutic focus should be lowering apo B levels to targets of <100 mg/dL for high-risk patients and <80 mg/dL for very high-risk patients, using statin therapy as first-line treatment. 4
Apo B measurement is particularly valuable in patients with metabolic syndrome, chronic kidney disease, or diabetes, where discordance between LDL-C and actual atherogenic particle number is common. 4