Improving the quality of plasma cholesterol measurements in primary care.

During the last 2 years an external quality assessment (EQA) scheme has been developed for plasma cholesterol measurements made in primary care. The scheme, which is supported by the UK Department of Health and by the instrument manufacturers, now has over 300 participants, most of whom use the Boehringer Reflotron. Operators are mostly nurses, with little or no laboratory experience. To avoid matrix effects, fresh plasma specimens collected from normal volunteers and those attending a hospital lipid clinic are used. Three specimens, mostly with cholesterol concentrations in the range 5-9 mmol/L, are distributed every 2 months. The mean plasma cholesterol results show good agreement with those from 'reference' laboratories, and efforts are now being made to link these laboratories with the CDC-based reference system. The scheme uses a predominantly graphical presentation of results, with a greater element of interpretation by the organisers than is usually provided for laboratory-based participants. The distribution of results shows a higher proportion of outliers than in the UK national EQA scheme for laboratory cholesterol measurements. At present about 10% of participants in primary care obtain results which could be clinically misleading, and new approaches are needed in dealing with these 'poor performers'. This scheme could serve as a model for other assays in primary care. It illustrates the importance of training, quality assurance and education, and the need for laboratory staff to become more involved in this growing and important area of laboratory medicine.