Background: PYY is a gut hormone that physiologically inhibits appetite. Currently only radioimmunoassay (RIA) techniques are available for its estimation. The aim of the study was to evaluate our in-house assay for precision, detection limit, interference of haemolysis, suitability of serum versus plasma and biological variation within one subject.
Method: All samples were obtained from one subject on two occasions following an over night fast and the consumption of 1000 and 3000 kcal meals on the respective days. Plasma was aliquoted in multiple samples. Coefficient of variation (CV) was measured at three concentrations (13.4, 16.4, 31.7pmol/L). The influence of haemolysis was evaluated by diluting severely haemolysed blood with non haemolysed blood obtained at the same venepuncture. All plasma samples were obtained in lithium heparin and trasylol tubes. Serum samples were obtained in a tube with trasylol and a clot activator. Carry over and the detection limit of the assay were also evaluated.
Results: Fasting samples obtained from the same individual on two occasions were comparable. The CV at 13.4, 16.4, 31.7 pmol/L was 19.7%, 13.4% and 12.5% respectively. Severe haemolysis affected the measurement, but slightly haemolysed plasma gave results similar to non haemolysed samples. Plasma samples were superior to serum samples. There was no evidence of significant carry over and the detection limit of this assay was 5pmol/L.
Conclusions: Plasma is the preferred source for sample for this assay which has a detection limit of 5pmol/L. Only severe haemolysis should be avoided. Carry over does not seem to be a problem and the CV of the assay is acceptable and does not vary within the physiological range of PYY.