Comparison of Serum and Heparinized Plasma Samples for Measurement of Chemistry Analytes

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Abstract
Although serum and heparinized plasma specimens are considered equivalent for many assays, differences in results between these two sample types have been reported for several chemistry analytes. Significant differences between serum and heparinized plasma results have been reported for albumin, alkaline phosphatase, calcium, carbon dioxide, chloride, creatine kinase, glucose, lactate dehydrogenase (LD), inorganic phosphorus, potassium, and total protein (1). The concentration differences in results for calcium, glucose, inorganic phosphorus, potassium, and total protein between serum and heparinized plasma were felt to be large enough to affect clinical interpretation in certain instances. The aim of this study was to compare results from serum and heparinized plasma samples for 45 different chemistry tests. Twenty apparently healthy volunteers who had been fasting for 12–14 h had serum and lithium-heparin specimens collected in that standard draw order during a single venipuncture. All studies conducted with human samples were approved by the Institutional Review Board of the University of Utah. The samples were centrifuged, serum and plasma were separated from cells within 1 h of collection, and 1-mL aliquots were frozen within 2 h of collection and stored at −70 °C for up to 8 months. Before analysis, the aliquots were thawed and mixed well. Matched aliquots of serum and heparinized plasma …