ApoB and ApoA‑1 are apolipoproteins: protein components of lipoprotein particles that transport cholesterol and triglycerides in blood. ApoB is found on LDL, VLDL, and other atherogenic particles and serves as a marker of particle number; ApoA‑1 is the primary protein of HDL and is involved in reverse cholesterol transport and lipid exchange. The ApoB/ApoA‑1 ratio combines these two measures into a single index of lipid particle balance. Clinically, the ratio has been studied as a complement to conventional cholesterol measures because it captures particle-level relationships rather than just cholesterol mass. Research over decades has shown that comparing atherogenic particle count to protective HDL-associated protein can highlight patterns of lipid-related risk that do not always appear when looking at total cholesterol or LDL cholesterol alone.

Higher ApoB/ApoA‑1 ratios are associated with a greater relative number of atherogenic particles compared with protective HDL particles. In clinical studies this pattern often aligns with other markers of metabolic stress, inflammation, or elevated atherogenic lipids, suggesting a lipid profile that may be more likely to coincide with vascular stress markers. Interpretation should consider the whole Cardio Zoomer panel—ApoB, LDL particle characteristics, Lp(a), inflammatory markers, and genetics—to understand drivers and context. Lower ApoB/ApoA‑1 ratios indicate relatively fewer ApoB-bearing particles compared with ApoA‑1, a pattern that frequently corresponds with more favorable lipid particle balance. Low ratios must also be interpreted alongside other biomarkers and clinical factors, since genetics, recent illness, or changes in lipid metabolism can influence apolipoprotein levels independently.

Cardio Zoomer includes ApoB/ApoA‑1 to assess the balance between atherogenic and protective lipoprotein particles. As a summary metric, the ratio helps clinicians see whether lipid-related risk is driven by particle burden, lack of HDL‑associated capacity, or a mix—information that complements inflammation, oxidative stress, and genetic markers to support personalized risk patterning.