What is the specimen of choice for glucose determination?

The specimen of choice for glucose determination is fluorinated plasma. Fluorinated plasma is obtained from blood that has been treated with a fluoride anticoagulant, such as sodium fluoride. The presence of fluoride inhibits glycolysis, the metabolic pathway that breaks down glucose, thus preventing any decrease in glucose concentration in the sample before analysis. This preservation of glucose levels makes fluorinated plasma highly reliable for enzymatic assays measuring glucose concentrations.

In contrast, while whole blood and serum can also be used for glucose measurement, they are more susceptible to changes due to glycolytic activity. Whole blood can show a decrease in glucose levels if not processed quickly, as red blood cells consume glucose for energy. Serum, although it can provide accurate results if processed immediately, can still be affected by the same glycolytic processes if the sample is allowed to sit for too long. Urine can be used to determine glucose levels, especially in cases of diabetes mellitus, but it may not reflect immediate glucose levels in the bloodstream and is not considered the first choice for quantitative analysis in a clinical laboratory setting.

Therefore, fluorinated plasma is preferred due to its ability to ensure accurate glucose measurements without the risk of changes from glycolytic activity.