The next time you go in for a medical checkup, your doctor will probably make a mistake that could endanger your life, contends cardiologist Allan Sniderman of McGill University in Montreal, Canada.

Most physicians order what he considers the wrong test to gauge heart disease risk: a standard cholesterol readout, which may indicate levels of low-density lipoprotein (LDL) or non-high density lipoprotein (non-HDL) cholesterol. What they should request instead, Sniderman argues, is an inexpensive assay for a blood protein known as apolipoprotein B (apoB).