Lipoprotein(A) determination and risk of cardiovascular disease in South African patients with familial hypercholesterolaemia

Objective. A raised plasma level of lipoprotein(a) (Lp(a)) is an establishe d genetic risk factor for coronary heart disease (CHD) particularly in pati ents with concomitant elevation of low-density Lipoprotein (LDL) cholestero l. The current study focused on the comparison of two commercially availabl e Lp(a) assay kits to determine whether differences observed in measured Lp (a) levels could be deemed negligible in CHD risk assessment in familial hy percholesterolaemic (FH) patients. Design. To compare results obtained on duplicate plasma samples using two c ommercially available Lp(a) measuring kits, the immunoradiometric assay (RI A) and the enzymelinked immunoabsorbent assay (ELISA). Setting. Division of Human Genetics, Department of Obstetrics and Gynaecolo gy, University of Stellenbosch, Tygerberg, South Africa and the Institute f or Medical Biology and Human Genetics, University of Innsbruck, Austria. Subjects. Plasma samples were obtained from 146 family members of 65 molecu larly characterised South African FH families for comparative analysis. Results. Using the RLA method, 34 samples (23%) considered to be in the nor mal range by the ELISA technique, were placed in the high-risk group (> 30 mg/dl). Only one sample, considered to have a normal Lp(a) level with the R IA method, was categorised by the ELISA technique as high risk. Conclusion. Our data demonstrate that measurements of Lp(a) using the RTA m ethod (the only assay available in South Africa at the time of this study) differ significantly from those obtained by the reference ELISA technique, suggesting that misclassification could lead to inaccurate CHD risk assessm ent. This is an important consideration in Afrikaner FH families, where pla sma levels of Lp(a) have been shown to be elevated significantly in FH pati ents compared with non-FH individuals.