Screening fasting glucose before the OGTT: near-patient glucometer- or laboratory-based measurement?

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The measurement of fasting glucose is a common practice for lowering the risk of hyperglycemia before an oral glucose tolerance test (OGTT). In this study we analyze advantages and limitations of near-patient measurement of capillary fasting glucose with a portable glucometer or blood sampling and measurement of plasma glucose with laboratory instrumentation. The final study population consisted of 241 subjects (mean age: 36±8 years; 97.9 % pregnant women) referred to our local phlebotomy center for an OGTT. Fasting glucose was measured in capillary blood using a near-patient glucometer (glucometer-based strategy) and in plasma with laboratory instrumentation using the hexokinase reference assay (laboratory-based strategy). The mean turnaround time from sample collection to obtaining the glucose value was longer with the laboratory-based strategy (32 min 8 vs. 8 s). The imprecision of the glucometer was higher than that of the laboratory assay (3.4 vs. 0.8 %). A negative bias of-3.3 % in fasting glucose was found with the glucometer compared to the laboratory measurement. The diagnostic accuracy, sensitivity and specificity of the glucometer for detecting fasting glucose values≥7.0 mmol/L were 99.2 , 50.0 and 100.0 % compared to the laboratory assay. The glucometer-based strategy had an incremental cost of 0.17€ per patient compared to the laboratory-based strategy. Screening fasting glucose in capillary blood with a near-patient glucometer instead of measuring fasting plasma glucose with laboratory instrumentation allows faster patient management in the phlebotomy center but is associated with higher imprecision, inaccuracy, costs and avoidable finger pricks.