Interference Due to Lipaemia in Routine Photometric Analysis—Survey of an Underrated Problem

Abstract

Traditionally external quality assessment schemes (EQAS) distribute samples spectrally similar to a normal serum. This does not allow laboratories to assess the performance of their methods at measuring lipaemic samples. The Irish EQAS distributed a sample with a supplied lipid diluent. A sample of the same batch had previously been circulated as a normal distribution to obtain baseline values. Most analytes were affected by the lipaemia. The degree of interference was instrument/method dependent and a wide range of values was reported for each analyte: total protein 51–134 g/L (baseline 65 g/L); albumin 33–56 g/L (baseline 42 g/L); calcium 2·12–6·10 mmol/L (baseline 2·34 mmol/L); urate 38–1100μmol/L (baseline 195μmol/L); creatinine 6–199μmol/L (baseline 140μmol/L); glucose 4·2–9·5 mmol/L (baseline 4·8 mmol/L); total bilirubin 1–192μmol/L (baseline 36μmol/L); urea 1·1–8·1 mmol/L (baseline 3·8 mmol/L); aspartate aminotransferase (AST) 12–105 iu/L (baseline 44 iu/L); iron 4·3–107μmol/L (baseline 26·8μmol/L); inorganic phosphorus 1·12–4·96 mmol/L (baseline 1·59 mmol/L); and cholesterol 2·5–17·1 mmol/L (baseline 4·1 mmol/L). In situations where no clearing of the lipid occurs in the reagent, interference can be minimized by taking a sample blank reading or using a kinetic procedure. If clearing of the lipid does occur, time must be allowed for this to be completed before analytical readings are taken.