Variability in the measurement of lipoprotein(a) in the British Isles

Mike Mackness1 and Elizabeth Hughes2; On behalf of the HEART, UK Laboratory Subcommittee

1Division of Cardiovascular Sciences, University of Manchester, Manchester; 2Department of Clinical Biochemistry, Sandwell General Hospital, West Bromwich, UK

Corresponding author: Mike Mackness, Division of Cardiovascular Sciences, University of Manchester, Department of Medicine, Manchester Royal Infirmary, Oxford Road, Manchester M13 9WL, UK. Email: (JavaScript must be enabled to view this email address)

Abstract

Background: Elevated Lipoprotein(a) concentrations are a risk factor for coronary heart disease; however, methodological problems have prevented its introduction to routine clinical practice.

Methods: Thirty-six laboratories each assayed 20 samples (the same 20 in each laboratory) using two different Lp(a) kits per laboratory, randomly assigned from the total of 12 used in the study.

Results: The duplicate error, i.e. the error between-duplicate analyses for each sample, for all kits was small, indicating all kits had a good precision for all the assays. However, there was a very large variation between the kits in the Lp(a) concentration assigned to a sample that could be over 100%. All methods showed a negative or positive bias as the concentration of Lp(a) increased. Most worryingly, as used in this study, several Lp(a) kits detected Lp(a) in a solution of 5% bovine serum albumin in phosphate-buffered saline. The between-laboratory variation in Lp(a) concentration measured using the same kit was very large, e.g. for a sample with a mean concentration of 78.8 mg/dL Lp(a) the between-laboratory variation was 29.7 mg/dL (37.7%). Even with samples with a relatively low Lp(a) concentration of 16.0 mg/dL had a between-laboratory variation of 12.3 mg/dL (76.8%).

Conclusion: There is wide variability in reported Lp(a) concentrations, assayed in the same sample, using different Lp(a) assays. At the present time these differences prevent the use of Lp(a) as a routine diagnostic tool.

Ann Clin Biochem 2009; 46: 311–315. DOI: 10.1258/acb.2009.08166