Influence of successive manual pipetting of multiple samples on precision and reliability of glucose test results

Abstract

Air-displacement micropipettes are precision equipment; however, they are affected by temperature change. The study investigated whether hand warmth generated during successive manually pipetting 10 µL in multiple samples using air-displacement micropipette can influence accuracy of glucose estimations. Venous blood sample (5 ml) was collected from an informed and a consented apparently healthy normoglycaemic adult (male) following ethical approval. One hundred replicates from aliquot plasma were divided into five ranges (R1-R5) of twenty replicates each for fasting plasma glucose (FPG) estimation. Gilson P20 air-displacement micropipette (Gilson, UK) was adjusted to pipette 10 µL manually under routine and repeatability conditions by an experienced analyst. Relative humidity, room temperature and analyst’s palm temperature were recorded before and after successive manual pipetting. FPG level was determined using Glucose-oxidase (GOx) method, and intra-analyst coefficient of variation (CV) calculated. Data were analyzed using descriptive statistics and one-way analysis of variance; association among variables was determined by Pearson’s correlation analysis, and significant level was set at p < 0.05. Duration of successive holding micropipette while manually pipetting 100 replicates in five ranges correlated positively with analyst’s palm temperature (r = 0.881, p = 0.048). Replicates in range 5 (81-100) had a significantly decreased FPG level (p = 0.000) with intra-analyst CV of 8.8% compared to ranges. Results suggest that under routine laboratory and repeatability conditions, successive manual pipetting of 10 µL more than 640 seconds or 60 samples using air-displacement micropipette may result in significant volume errors with imprecise glucose estimates.