Radioimmunoassay of β-Thromboglobulin: False High Values from Frozen Plasma Samples

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Abstract
Aliquots of plasma samples assayed after storage at −26 °C can show a significantly higher level of measured β-thromboglobulin (β-TG) than the corresponding unstored aliquots. Blood spun at the recommended speed of 1,800 × g still contains platelets that will release β-TG on freezing to yield false results—a point that has not been stressed in the literature. Aliquots of blood plasma spun at either 1,800 × g (low speed [LS]) or 20,000 × g (high speed [HS]) were assayed by radioimmunoassay fresh and after storage at 4 °C or −26 °C. Storage at −26 °C increased mean β-TG values of fresh or 4 °C stored LS samples from 0.78 to 1.94 nmol/L (28-70 ng/mL), whereas all HS mean values were ± 0.51 nmol/L (between 18 and 19 ng/mL). The authors believe that in addition to the accepted precautions regarding blood sampling and handling, it is essential to stress that for accurate measurement of β-TG in plasma, samples should be centrifuged at HS or, if this is not feasible, that they be assayed as soon as possible without prior freezing.