Abstract
IntroductionHaemolysis is the leading cause of sample rejection in laboratory haemostasis. Most studies focused on artificially haemolysed samples. The aim of this study was a prospective assessment of spontaneous haemolysis on haemostasis tests, by comparing results of haemolysed (H) versus new, non-haemolysed (NH) specimens, collected within 4hrs. As new coagulometers can identify interfering substances, visual assessment of haemolysis was also compared with instrumental haemolysis index and stratified in subclasses.Materials and methodsTwo hundred and sixty nine paired samples were collected and analysed using ACL TOP750-CTS (Instrumentation Laboratory, Bedford, USA), for prothrombin time (PT), activated partial thromboplastin time (aPTT), D-Dimer (DD), fibrinogen (Fib) and antithrombin (AT). Bias between H and NH was calculated and compared with the respective critical difference (CD).ResultsMean bias was - 0.1 s for PT (P = 0.057), - 1.1 s for aPTT (P < 0.001), 1025 ng/mL for DD (P < 0.001), - 0.04 g/L for Fib (P = 0.258) and 1.4% for AT (P = 0.013). Bias exceeding the CD varied according to the method, with larger differences for aPTT (36.1%) and DD (17.1%) and < 8% for PT, Fib and AT. No correlation emerged between free haemoglobin values and difference in haemostasis tests in H and NH samples for any tests. Moderate/severe haemolysis involved > 95% of samples. The agreement between visual assessment and instrumental evaluation of haemolysis was 0.62.ConclusionSpurious haemolysis deeply influences aPTT and DD, and to a lesser extent AT and Fib. Prothrombin time seems only slightly influenced, suggesting that PT can be accepted also in haemolysed samples. Although a good inter-observer correlation of haemolysis evaluation was found, the instrumental assessment of haemolysis seems recommendable.
Highlights
Haemolysis is the leading cause of sample rejection in laboratory haemostasis
Among the various preanalytical problems, haemolysis is the leading non-conformity, for samples collected for haemostasis testing
A vague indication is only contained in a separate article, which identified an free haemoglobin (fHb) value of 0.6 g/L as the maximum tolerable cut-off for haemolysis, above which test performance would be biased [4]
Summary
Haemolysis is the leading cause of sample rejection in laboratory haemostasis. Most studies focused on artificially haemolysed samples. The aim of this study was a prospective assessment of spontaneous haemolysis on haemostasis tests, by comparing results of haemolysed (H) versus new, non-haemolysed (NH) specimens, collected within 4hrs. Among the various preanalytical problems, haemolysis is the leading non-conformity, for samples collected for haemostasis testing. The guidelines of the British Committee for Standards in Haematology (BCSH) recommend rejecting haemolysed samples, but no distinction is made based on the haemolysis grade [3]. Even more importantly, both documents failed to provide straightforward thresholds of cell free haemoglobin (fHb) after which haemostasis testing would be analytically and clinically biased. A vague indication is only contained in a separate article, which identified an fHb value of 0.6 g/L as the maximum tolerable cut-off for haemolysis, above which test performance would be biased [4]
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