Serum index rules prevent risk of analysing uncentrifuged tubes on automated biochemistry analysers

Around 1.5% of the total clinical biochemistry tests performed in laboratories are affected by preanalytical errors. Large, automated chemistry analysers prevent errors and interference by using control systems such as spectrophotometric measurements to evaluate serum indices, i.e. haemolysis (H), icterus (I), and lipemia/turbidity (L). However, still preanalytical errors can remain undetected. Our laboratory experienced an incident caused by laboratory-induced preanalytical errors, where approximately 100 sedimented lithium heparin samples bypassed centrifugation and entered our automated analyser. Based on index results, we investigated the possibility of using turbidimetry measurement, as a mean to prevent analysis on uncentrifuged sedimented whole blood. 14078 L-indices from 8 days in August 2019 were extracted from the middleware and used to develop and evaluate stop rules. Similarly, a one-day validation dataset was identified in December 2020 and used for an independent validation. Three different types of stop rules were evaluated: (1) A single L-index result above a cut-off; (2) A sequence of an L-index results above a cut-off; (3) A simple moving average of n results above a cut-off. A stop rule using 3 consecutive L-indices of 40-60 was found to be superior. However, practical implementation in the instrument middleware on a Roche Cobas 8000 only allowed a simple moving average of 110 (n = 5). This rule was found to be able to identify and stop sedimented whole blood analysis. Additionally, the rule has minimal impact on daily routine production in the laboratory.