Authors (including presenting author) :
So CF, Yeung MHT, Wong MT, Wong YL, Ling TK, Lam CW
Affiliation :
Division of Chemical Pathology, Department of Pathology, Queen Mary Hospital, Hong Kong West Cluster, Hospital Authority
Introduction :
Citrate contamination of clinical laboratory specimens, although uncommon, can produce spurious laboratory results and lead to unnecessary treatment which is potentially life-threatening. It is often the result of the inappropriate introduction of sodium citrate (an additive commonly used for clotting profiles)-containing blood to another specimen container for tests incompatible with sodium citrate. Retrospective in-house audit identified 8 cases of potentially contaminated cases within 12 months. A rapid algorithm is therefore needed to detect citrate contamination at our centre. Here we present a rapid algorithm for the detection of citrate contamination. The validity of the rapid algorithm is supported by mass spectrometry citrate peak height analysis, with significantly elevated citrate peak height in contaminated samples compared to controls.
Objectives :
To implement a rapid algorithm in the laboratory middleware to identify citrate contaminated samples.
Methodology :
Residual plasma from 21 random specimens was divided into two lots. One lot was intentionally contaminated with sodium citrate by the transfer of specimens from their original blood collection tubes into unused sodium citrate blood tubes. Another lot served as the control without sodium citrate contamination. The sodium and chloride concentrations of the citrate-contaminated and control samples were analysed on the Cobas 8000 modular analyzer series which utilise indirect ion-selective electrodes to measure sodium and chloride concentrations. Ionised calcium concentrations of the samples were then determined by the Siemens RAPIDPoint 500e blood gas analyzer. Finally, mass spectrometry was performed to confirm citrate contamination in the contaminated samples through citrate peak height analysis using a peak height cutoff of 1.0 × 106 to differentiate between samples with and without citrate contamination.
Result & Outcome :
Using sodium-to-chloride ratio and sodium concentration cutoff values of >1.55 and > 145 mmol/L respectively, the rapid algorithm was able to identify all citrate-contaminated samples, with elevated sodium-to-chloride ratios above 1.55 and undetectable ionised calcium (<0.55 mmol/L). On the other hand, the sodium-to-chloride ratios were below 1.55 with detectable ionised calcium levels in all control samples. Analysis by mass spectrometry on the 21 citrate-contaminated samples showed an at least 10-fold increase in citrate peak areas when compared to the controls. Our rapid algorithm effectively detects citrate contamination for routine clinical use. It has been implemented in our middleware since 18 Dec 2024 to prevent reporting of erroneous laboratory results and avoid future AIRS incidents. Proper blood taking should be reinforced, emphasizing that transferring blood between different tube types is strictly prohibited, in order to prevent unnecessary wastage of resources for AIRS incident investigation.
