Right or wrong sample received for coagulation testing? Tentative algorithms for detection of an incorrect type of sample

Abstract

Inappropriate blood collection potentially comprises the major pre-analytical problem for coagulation testing. Inappropriate samples are most difficult to detect when received as secondary aliquots, common for referred tests. This study aimed to identify a simple, quick and inexpensive process to help laboratories distinguish the type of sample, should there be suspicion of inappropriate collection. Samples from 15 patients [selected on the basis that four different primary tubes were available: serum, citrated plasma, ethylene diamine tetraacetic acid (EDTA) plasma, lithium-heparin plasma], were tested for common electrolytes that might substantially differ according to the type of sample. In citrated plasma, potassium, chloride, calcium and magnesium were significantly decreased compared with serum and lithium-heparin plasma, while sodium was markedly increased. In EDTA plasma, sodium and chloride were significantly decreased compared with both serum and lithium-heparin plasma, potassium was always >14 mmol/l, whereas magnesium and calcium were virtually undetectable. These data allowed development of two algorithms for differential identification of citrated plasma vs. other samples with 100% sensitivity and specificity, the former based on the sequential measurement of potassium, calcium and sodium, the latter on potassium and sodium. These simple assays can supplement classical coagulation test methods to identify most inappropriate blood collections and validate sample rejection.

Pre-analytical issues in the haemostasis laboratory: guidance for the clinical laboratories

“…It is easy to ensure that the anticoagulant is consistent when working on the primary tube; vigilance is therefore required in case of analysis performed on an aliquot [53]. …”

Underestimation of plasma level of factor V coagulant activity and fibrinogen concentration together with prolonged prothrombin time, activated partial thromboplastin time and thrombin time can result from pre‐analytical very low calcium level in citrated sample tube

“…Moreover, the results we obtained with the 20 EDTA normal samples are very similar to those observed with the 17 ‘Ca 0’ samples. As described by Lippi and colleagues , very low Ca concentrations are characteristic of EDTA samples, together with undetectable magnesium concentrations and very high concentration of potassium. This improper anticoagulant present in a citrated tube could result from decanting part of an EDTA sample to an insufficiently filled citrated tube leading to an utmost imbalance of the citrate–calcium ratio.…”

Sodium citrate blood contamination by K2‐ethylenediaminetetraacetic acid (EDTA): impact on routine coagulation testing

“…Although the contamination of citrated blood with EDTA salts can be largely avoided by following appropriate recommendations and guidelines , such contamination can occur because of a variety of events and can thus be considered as anything but unlikely in the common practice of collecting and handling blood specimens. This has also led to development of specific algorithms for the effective detection of such contamination . When contaminating sodium citrate‐anticoagulated blood, the powerful chelating effect of the EDTA additive leads to sequestration of not only the calcium in the whole blood sample, but also the subsequent conventional amount of calcium that is added to the sample in the instrument cuvette to initiate the clotting tests.…”