Lipoprotein Lp(a) and the risk for myocardial infarction

The serum lipoprotein Lp(a) concentration was measured in 76 male post-myocardial infarction (MI) patients aged between 40 and 60 years, and in 107 control subjects of the same age and sex. Quantitation was performed by the Laurell technique. It was sensitive in the range 1–60 mg/dl with a day to day C. V. of less than 4%. A considerable variation of Lp(a) concentration was noticed in the whole population with a frequency distribution of higher order. Conventional statistical methods could therefore not be applied to evaluate a possible MI risk of Lp(a). In addition to Lp(a), several other risk and anti-risk factors for atherosclerosis were assayed. The whole population was divided into normolipemics (NL) and Type IIa, IIb and IV phenotypes. In addition, the subjects were grouped into two or three Lp(a)-types, selecting several different cut-off points for Lp(a) concentrations. The results can be summarized as follows: (1) NL-controls had significantly lower total cholesterol and low density lipoprotein (LDL)-cholesterol but higher high density lipoprotein (HDL)-cholesterol values compared to the MI-patients. The HDL-cholesterol concentration was also significantly different between Type IIa controls and MI-patients. (2) Eleven per cent of the NL-controls but 25% of the NL-MI-patients exhibited Lp(a) values exceeding 50 mg/dl. Thus Lp(a) concentration above this value represents a 2.3-fold relative risk for MI. Similar findings were obtained in the Type IIa and IIb populations but not in Type IV hyperlipemics. (3) Taking 30 mg/dl as the cut-off point, Lp(a) represents a relative risk of 1.75 for MI in the NL population. (4) Hyperlipemics in general (controls + MI) exhibited higher Lp(a) values compared to NL. (5) Statistical evaluation of all the data failed to reveal any correlation between Lp(a) levels and other risk or anti-risk factors for atherosclerosis. (6) It is concluded that Lp(a) represents an independent addi tional risk factor for MI with a possible threshold value of approx. 30 mg/dl in NL.