Lipoprotein-Associated Phospholipase A2 (Lp-PLA2)

The numbers feel precise, but notice how much rides on which line a lab chooses. The same draw can read "borderline" against the single 225 cutoff and "normal" against a man's 250, or "elevated" against a woman's 200. A test that genuinely isolated dangerous plaque activity would not depend so heavily on where the percentile knife falls.

The intuitive reading is that a high Lp-PLA2 means the enzyme is busy chewing up oxidized cholesterol in your artery walls, so the walls must be inflamed and unstable. People often arrive with exactly this worry: my Lp-PLA2 is high, does this mean I have plaque. The honest answer is more deflating. Because the enzyme is mostly a passenger on LDL, a high number frequently means there is a lot of LDL for it to ride on.

The evidence for the impostor reading is unusually direct. The American Academy of Family Physicians reports that once you adjust for the standard risk factors, including BMI, diabetes, smoking, blood pressure, cholesterol, and CRP, the test's predictive association was no longer statistically significant. After the things your doctor already measures are accounted for, the extra warning Lp-PLA2 seemed to give mostly disappears. The same review puts its sensitivity at just 31% to 37% at the manufacturer cutoff, so the test misses most of the people who go on to have events.

There is a real argument on the other side. Unlike hs-CRP, which the liver makes in response to inflammation anywhere in the body, Lp-PLA2 is produced by macrophages and foam cells inside the plaque itself, which is why some research describes it as a relatively vascular-specific signal. So the enzyme is not pure noise. The problem is the arithmetic of one measurement: the plaque-made portion and the LDL-riding portion arrive added together, and the report cannot tell you which is which.

If Lp-PLA2 caused unstable plaque, lowering it should make hearts safer. That hypothesis was tested at scale, and it failed. The STABILITY trial, summarized by the American College of Cardiology, gave the drug darapladib to 15,828 patients with established coronary artery disease and followed them for a median of 3.7 years. Darapladib lowered Lp-PLA2 markedly. It did not reduce the combined rate of cardiovascular death, heart attack, and stroke: 9.7% on the drug versus 10.4% on placebo, a hazard ratio of 0.94 with a confidence interval crossing 1 and a p-value of 0.20.

That is the signature of a passenger, not a cause. A marker that travels with risk but does not create it will fall when you target it and leave the outcomes untouched, which is what happened here. The number reflects the convoy more than the road.

Lp-PLA2 sits in the cardiac panel among markers that try to add detail beyond the basic lipids, and it overlaps most with the very numbers it rides on. The particle count carrying cholesterol into the artery wall is read by apolipoprotein B, and a separately inherited risk lipid is measured as lipoprotein(a); both tell you things Lp-PLA2 largely cannot. For inflammation, hs-CRP answers the body-wide question while galectin-3 speaks more to fibrosis and heart-failure risk. The guide to reading cardiac markers walks through where each one earns its place, and the guide to reading inflammation markers covers how a vessel-made signal differs from a liver-made one.

Because so much of a single Lp-PLA2 value is borrowed from the LDL it travels with, one reading in isolation is the least informative way to use it. What a clinician can sometimes use is the direction over time once the lipids are stable, since that trend is the only way to tell a real change in vessel-wall activity from the convoy getting larger.