ABSTRACT
Dyslipidaemia is a major risk factor for coronary heart disease which can be assessed by measuring serum lipid profile. Biological variation has an important effect on the interpretation of all laboratory investigations, including lipid profile. To define the biological and analytical components of variation for the different parameters of serum lipid profile. The present study was conducted in Mosul City in northern Iraq, from 1[st] February to 30[th] April 2004. Fasting venous blood was collected from each of 10 apparently healthy volunteers [6 men and 4 women, aged 22-40 years], at 8-10 am following an overnight fast, at intervals of one week for 10 weeks. Sera were separated and stored frozen, in duplicate. Measurement and calculation of the different components of serum lipid profile were made including: triglycerides [TG], total cholesterol, HDL-C, LDL-C and ratios of total cholesterol: HDL-C, LDL-C: HDL-C and TG: HDL-C. The intra-individual [CVI] and inter-individual [CV[G]] variation were 21% and 37% for TG, 7.5% and 16.7% for total cholesterol, 11.2% and 24.5% for HDL-C, 13.7% and 28.3% for LDL-C, 13.1% and 25.4% for total cholesterol: HDL-C, 25.9% and 34.7% for LDL-C: HDL-C, and 27.2% and 40.7% for TG: HDL-C respectively. The indices of individuality, as reflected by CVI/CVG, for these parameters were all <1.0 [0.57 for TG, 0.45 for total cholesterol, 0.46 for HDL-C, 0.48 for LDL-C, 0.52 for total cholesterol: HDL-C, 0.95 for LDL-C: HDL-C and 0.85 for TG: HDL-C]. The analytical goals for imprecision, as reflected by analytical variation [CVA], was 6.3% for TG, 4.0% for total cholesterol, 5.2% for HDL-C, 7.8% for LDL-C, 5.8% for total cholesterol: HDL-C, 5.7% for LDL-C: HDL-C and 5.9% for TG: HDL-C. The critical difference calculated as 2.77 [CVA[2]+ CVI[2]][1/2] was 60.7% for TG, 23.5% for total cholesterol, 34.2% for HDL-C, 43.6% for LDL-C, 39.7% for total cholesterol: HDL-C, 73.3% for LDL-C: HDL-C and 97.5% for TG: HDL-C. The biological and analytical components of variation showed marked individuality. This together with the index of individuality supports the limited usefulness of using the conventional population-based reference range for interpretive criteria. The critical differences also confirm that single determination of lipid profile may have limited value in screening purpose