RESUMO
BACKGROUND: Interfering substances such as haemoglobin, bilirubin and lipids in a sample may lead to wrong interpretation of immunoassay results by the clinician. In general, there has been minor attention to these interferences on immunoassays, whereas these effects on chemical assays are frequently described. Information about interferences by haemoglobin, bilirubin and lipids on the Siemens Immulite 2500 assays in the instructions for use is falling short. METHODS: Interferents in patient samples can be measured reliably in a semi-quantitative way on most chemistry analysers and can be expressed in haemolysis-, icterus- and lipaemia-indices. As the Immulite 2500 cannot perform such measurements, samples are normally analysed without testing for the presence of interferents. Therefore, a study was carried out to examine these interferences on 24 Immulite 2500 assays. Samples were spiked with increasing concentrations of either haemoglobin, bilirubin or lipids. The haemolysis-, icterus- and lipaemia-indices were measured on a Synchron DxC 800 analyser. RESULTS: Based on analytical imprecision and intraindividual biological variation of each analyte, cut-off indices above which clinically significant interference exists were determined. We found clinically significant interference due to haemoglobin on ferritin and folate, by bilirubin on oestradiol and testosterone and by lipids on testosterone. CONCLUSIONS: Introducing cut-off indices prevents reporting of wrong Immulite 2500 results due to interference. Our results are applicable in laboratories using any chemistry analyser capable of reporting semi-quantitative concentrations of interferents.