Inversion of lithium heparin gel tubes after centrifugation is a significant source of bias in clinical chemistry testing Giuseppe Lippi a, ⁎, Gian Luca Salvagno b , Elisa Danese b , Gabriel Lima-Oliveira b,c , Giorgio Brocco b , Gian Cesare Guidi b,c a Laboratory of Clinical Chemistry and Hematology, Academic Hospital of Parma, Parma, Italy b Laboratory of Clinical Biochemistry, Department of Life and Reproduction Sciences, University of Verona, Verona, Italy c Post-Graduate Program of Pharmaceutical Sciences, Department of Medical Pathology Federal University of Parana, Curitiba, Parana, Brazil abstract article info Article history: Received 4 April 2014 Received in revised form 19 May 2014 Accepted 19 May 2014 Available online 8 June 2014 Keywords: Preanalytical variability Serum Lithium heparin Gel tubes Blood collection 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 90 min (“upright”), whereas paired tubes underwent bottom-up inversion every 15 min, for 90 min (“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. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Serum or plasma separator tubes were introduced nearly 40 years ago and their use is now commonplace in laboratory diagnostics, since these devices carry a number of technical and practical advantages over plain tubes [1]. First, gel tubes ensure a greater analyte stability over time, regardless of the storage conditions [2,3]. Then, since the generation of a stable physical barrier between plasma or serum and the blood cells underneath can be obtained with a single centrifugation step, it reduces the need to aliquot specimens and allows a much greater degree of sam- ple manipulation after centrifugation, due to the virtually absent risk of contamination from the pellet [1]. Since the separator gel improves ana- lyte stability, this would permit to transfer centrifuged blood samples with various containers and means (e.g., safety bags, boxes, pneumatic tube systems), over long distances, and even in awkward conditions, with negligible impact on sample quality [4]. This is noteworthy, since the Clinical and Laboratory Standards Institute (CLSI) currently recom- mends that blood samples should be preferably centrifuged prior to transportation when the phlebotomy settings are relatively distant from the central laboratory [5], so that the physical separation of serum or plasma from blood cells by means of physical barriers (typically gel) may prevent the deterioration of several analytes during shipment of whole blood. The only major limitation stated by the manufacturers about sample handling is that gel barrier tubes should not be frozen, because the physical composition of the gel may be altered upon freezing and thawing, thus resulting in blood cells' contamination of serum or plasma. Although it is rather intuitive that plain tubes should always be kept in a vertical, closure-up position after centrifugation to avoid resuspen- sion of blood cells into the upper fluid, such an indication is not current- ly provided for gel tubes, based on the fact that the gel barrier remains intact when tubes are transported or manipulated. This paradigm has contributed to generate a broad confidence in the way centrifuged gel tubes are handled after centrifugation, with little concern that serum or plasma may be contaminated by blood cells even when the tubes are mixed, inverted or kept in non-vertical positions. It is also notewor- thy that the CLSI provides a generic recommendation about the orienta- tion of blood tubes during transportation, suggesting that “where possible, blood tubes should be kept in a vertical, closure-up position during transportation” [5]. The World Heath Organization (WHO) guidelines on drawing blood do not even clearly specify how samples Clinica Chimica Acta 436 (2014) 183–187 ⁎ Corresponding author at: U.O. Diagnostica Ematochimica, Azienda Ospedaliero- Universitaria di Parma, Via Gramsci, 14, 43126 Parma, Italy. Tel.: +39 0521 703050, +39 0521 703791. E-mail addresses: glippi@ao.pr.it, ulippi@tin.it (G. Lippi). http://dx.doi.org/10.1016/j.cca.2014.05.028 0009-8981/© 2014 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Clinica Chimica Acta journal homepage: www.elsevier.com/locate/clinchim