Inversion of lithium heparin gel tubes after centrifugation is a significant source of bias in clinical chemistry testing.

BACKGROUND: This study was planned to establish whether random orientation of gel tubes after centrifugation may impair sample quality. MATERIALS AND METHODS: Eight gel tubes were collected from 17 volunteers: 2 Becton Dickinson (BD) serum tubes, 2 Terumo serum tubes, 2 BD lithium heparin tubes and 2 Terumo lithium heparin tubes. One patient's tube for each category was kept in a vertical, closure-up position for 90min ("upright"), whereas paired tubes underwent bottom-up inversion every 15min, for 90min ("inverted"). Immediately after this period of time, 14 clinical chemistry analytes, serum indices and complete blood count were then assessed in all tubes. RESULTS: Significant increases were found for phosphate and lipaemic index in all inverted tubes, along with AST, calcium, cholesterol, LDH, potassium, hemolysis index, leukocytes, erythrocytes and platelets limited to lithium heparin tubes. The desirable quality specifications were exceeded for AST, LDH, and potassium in inverted lithium heparin tubes. Residual leukocytes, erythrocytes, platelets and cellular debris were also significantly increased in inverted lithium heparin tubes. CONCLUSIONS: Lithium heparin gel tubes should be maintained in a vertical, closure-up position after centrifugation.