ApoA1

Cholesterol does not dissolve in blood and therefore travels in particles with a protein on the outside. On the LDL particles and the other particles that can deposit cholesterol in the vessel wall that is ApoB; on the HDL particles, which bring cholesterol back out of the vessel wall and take it to the liver, that is ApoA1. That protein does more than hold the particles together: it switches on the enzyme that locks cholesterol inside the particle, and it is the key with which the particle collects cholesterol from the vessel wall. That difference decides what you measure. HDL cholesterol weighs how much cholesterol the HDL particles carry; ApoA1 counts the particles themselves. Two people with the same HDL cholesterol can have a different number of particles: one with few heavily loaded particles, the other with many light ones. Many particles with little cholesterol in them give a high ApoA1 with a modest HDL, and that means many collectors are circulating that still have room. Your report prints ApoA1 in g/L; unlike the cholesterol values you do not need to watch mmol/L against mg/dL here. Normal is roughly 1.04 to 1.78 g/L in men and 1.08 to 1.99 g/L in women, where the labs overlap, and women naturally sit slightly higher through oestrogen. Higher is favourable.

ApoA1 is the counterpart of ApoB: the one protein sits on the particles that can deposit cholesterol in the vessel wall, the other on the particles that take it back out. Anyone who measures both counts the supply and removal of cholesterol in particles instead of in weight, and the ratio between those two predicted the risk of a heart attack more strongly than LDL cholesterol in large studies. The second reason is that ApoA1 shows what lifestyle does to the collecting side. Exercise, losing weight and stopping smoking lift the number of HDL particles, and ApoA1 moves along. Belly fat, little exercise and insulin resistance lower it, as does smoking. A low ApoA1 with high triglycerides is the fat pattern of insulin resistance, and that is the pattern lifestyle changes most. The honest limitation is that the Dutch risk estimate does not work with it. It works with LDL and non-HDL, and does not recommend measuring apolipoproteins routinely. A high HDL, and so a high ApoA1, also protects less than was long thought: lifting HDL with medicines turned out not to prevent heart attacks. So read ApoA1 beside your HDL and ApoB, not instead of them, and let the decision on a statin fall on LDL and non-HDL.

A low ApoA1 means there are fewer particles bringing cholesterol back out of the vessel wall. Usually it is the first and rarely the last: excess weight, little movement and insulin resistance, the pattern that lowers HDL and pulls the carrying protein down with it; smoking, which lowers the number of HDL particles; and an underactive thyroid, which changes the whole fat balance. A low value therefore usually moves along with a low HDL, and the approach is the same. A high ApoA1 is favourable and belongs with a high HDL: more particles means more carrying protein, so the two usually move together. Regular exercise lifts it by the same route as HDL cholesterol, and women naturally sit higher through oestrogen; oestrogen in tablet form lifts it further still. If ApoA1 and HDL diverge, that says something about the loading of the particles: many particles with little cholesterol in them give a high ApoA1 with a modest HDL. ApoA1 belongs beside your HDL cholesterol, because the two describe the same particles from two sides, beside ApoB, because the ratio between those two is what this test is usually requested for, and beside the triglycerides, which show whether the pattern of insulin resistance is at play. Compare only with the band on your own report, because the two labs that publish one set it differently.