Background: Apart from utility of APTT Clot Waveform Analysis (CWA) in Hemophilia and Sepsis, our experience in assessing its utility for existence of pre-analytical error has been evaluated. This is based on absence of proper CWA pattern or specific derivatives of CWA in too short APTT samples.

Aims: To Evaluate APTT CWA in short APTT samples for presence of various derivatives and compare with those in repeat samples received.

Methods: Citrate samples received in 3.2% Trisodium Citrate vaccutainers with 9:1 proportion were subjected to stringent rejection criteria established by laboratory. APTT of accepted samples was processed on ACL TOP 300/500 analyser using SynthASil. CWA was analysed in short APTT samples (less than 25 seconds). Samples with improper CWA were rechecked for absence of fibrin threads. Repeat samples were obtained and reprocessed. Changes in CWA were compared with original CWA.

Results:
Period of Evaluation: Jan 2018 to Dec 2019
Citrates received: 52532
Citrates Rejected: 671 (1.27%)
Repeat Samples requested with short APTT: 178
Samples with change: 146
Samples without change: 32
Samples with fibrin threads: 09
Samples with Missing Pre Coagulation phase: 146
2^nd Derivative only: 76
1^st and 2^nd Derivative: 64
1^st, 2^nd and Clot curve: 06
Median of APTT value (seconds)
1^st Sample: 20.3
Repeat sample: 26.7

Conclusions: APTT CWA plays substantial role in identifying Preanalytical error in citrate samples which have been visually passed through rejection criteria. 2^nd Derivative in CWA, which represents coagulation acceleration or Prothrombinase activity, is first to disappear in our samples. Difficult collection is common in ICU settings. Release of Tissue factor at the site of collection activates extrinsic tenase formation thereby initiation of clotting in vivo at site of puncture. This shortens APTT value and missing derivatives in CWA are observed. This may be as part of activated sample.

[A: Short APTT with Missing Pre-Coagulation Phase in APTT CWA, B: Repeat Sample with proper APTT CWA]

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/aptt-clot-waveform-analysis-a-tool-in-prediction-of-pre-analytical-errors-in-short-aptt-retrospective-analysis/