Serum indices and analytical interference in clinical chemistry tests

Abstract

Interference in analyte measurements can be caused by multiple factors with two of the most common being haemolysis and icterus. Haemolysis is defined as the release of haemoglobin and other intracellular components into surrounding plasma due to the fragmentation of red cells. Icterus is defined as the yellow hue observed due to the presence of bilirubin in plasma, which is formed as a result of haeme catabolism in the liver. The effect of haemolysis on the measurements of the concentrations of a number of analytes was studied. These included Potassium, Lactate Dehydrogenase (LDH), Creatine Kinase (CK), Alanine Aminotransferase (ALT), Sodium, Procalcitonin and N-terminal-prohormone brain natriuretic peptide (NT-proBNP). The effect of icterus on the measurements of the concentrations of the following analytes was studied and these included Ammonia and Creatinine. The effects of both haemolysis and icterus on the measurement of the concentration of Cardiac Troponin T (cTnT) were tested. For the preparation of haemolysate the freeze-thaw method was carried out with 3 cycles over the course of three days followed by centrifugation. For icterus testing bilirubin in chemical form was used with dilutions being acquired by dissolving specific amounts for each dilution level. The haemolysate and icterus dilutions were spiked at five different dilution levels into pooled sera containing the high and low medical decision levels for each specific analyte used. Reference change values were used in order to determine clinically significant cut-offs. Suitable cut-offs were acquired for analytes such as potassium, CK and creatinine however many analytes showed disagreement with the expected results. This was due to a multitude of factors such as high degrees of variability in results gathered. The results also helped shed light upon the limitations of the study carried out.