Background: To minimise the volume of blood used for diagnostic procedures, especially in children, we investigated whether the size of sample tubes affected whole blood coagulation analyses.
Methods: We included 20 healthy individuals for rotational thromboelastometry (RoTEM®) analyses and compared three blood sampling tubes of different size: 1.8, 2.7, and 3.6 mL. All tubes were made of plastic and contained 3.2% sodium-citrate as anticoagulant. Platelet aggregation was investigated in 12 healthy individuals employing the Multiplate® Analyser comparing tubes of 3.6 mL and 1.8 mL. Platelet count was determined for each of the sampling tubes after 10, 60, and 120 min.
Results: No significant differences were found in any of the RoTEM® measurements between the three sizes of tubes (p=0.07-0.53). Platelet aggregation was significantly lower when using smaller tubes (p=0.0004). The platelet count remained stable using a 3.6 mL tube during the entire observation period of 120 min (p=0.74), but decreased significantly after 60 min when using tubes smaller than 3.6 mL (p<0.0001).
Conclusions: RoTEM® analyses were not affected by the size of blood sampling tubes. Therefore, 1.8 mL tubes should be preferred for RoTEM® analyses in order to minimise the volume of blood drawn. With regard to platelet aggregation analysed by impedance aggregometry tubes of different size cannot be used interchangeably. If platelet count is determined later than 10 min after blood sampling using tubes containing citrate as anticoagulant, a 3.6 mL tube should be preferred to avoid false low values.