Clot Signature Curve Analysis as a Useful Tool of Thrombin Time Measurement in Case of Failed Optical Reading
12 October 2018
05 February 2019
28 March 2019 (online)
A 69-year-old man with pancreatic head cancer was admitted to the hospital due to severe abdominal pain and generalised weakness. Complete blood count showed leukocytosis (22.65 × 109/L) with neutrophilia (18.80 × 109/L), biochemical tests showed high gamma-glutamyl transferase activity (350 U/L) and high C-reactive protein concentration (3,468.6 nmol/L). Patient was diagnosed with necrotising chemocystitis with bile duct perforation and referred for emergency surgery. Before surgery, coagulation tests were performed using an ACL TOP 500 analyser and Instrumentation Laboratory reagents (Werfen, Bedford, MA, United States). The obtained results showed international normalized ratio (INR) 1.08, prothrombin time 12.4 seconds (ref. 11.5), activated partial thromboplastin time 31.3 seconds, fibrinogen 8.6 g/L, and d-dimers 2,118 μg/L. The analyser did not show results for thrombin time and presented the alarm ‘failed’, indicating that the parameters of the reaction curve ([Fig. 1A]) did not meet the predetermined conditions for clot formation process ([Fig. 1B]).
Despite the lack of numerical results, the patient's reaction curve showed a typical increase of absorbance, which suggested sufficient fibrin formation. The first and second derivatives of the curve presented maxima, which confirmed clot formation in a test cuvette. Basing on the maximum of a second derivative, thrombin time was estimated at 12 seconds for basic and 13 seconds for analysis with extended time. To confirm the results of thrombin time analysis, it was repeated with a manual method using a water bath and thrombin time reagent (Instrumentation Laboratory). In the manual method, plasma clotted within 12 seconds; however, clot structure was assessed as abnormal (loose). Both the automated and manual method results might suggest impaired fibrin polymerisation, which could result in increased risk of intraoperative haemorrhage.
Based on the clot signature curve in the presented case, coagulation was not impaired and the lack of results should be considered as a laboratory error in the analytical phase. The patient underwent surgery with no bleeding complications. Increase of a sample absorbance in the first few seconds of analysis might be associated with dysfibrinogenaemia with spontaneous fibrin formation, disseminated intravascular coagulation (DIC) or interference from a high concentration of acute phase reactants in the analysed plasma, including fibrinogen.   DIC with balanced fibrinolysis is associated with increased concentration of fibrin and fibrinogen degradation products which incorporate in fibrin web and impair its structure. Enhanced coagulation, expressed by high level of d-dimers, could induce fibrin generation in tested plasma before reagent (thrombin) addition. It might increase sample absorbance and elevation of typically flat baseline, thus affecting measurement of thrombin time by optical method.
Here we show that proper interpretation of laboratory test results should not be based only on numerical results, but also on analysis of visual representation of a result (curves, scattergrams, histograms), which directly reflects analytical processes in the analyser. Appropriate interpretation of graphical laboratory test results should be annotated on the final laboratory report, since it may influence the therapeutic decisions and final diagnosis.
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