Background: To prevent excessive bleeding during delivery, pregnancy causes a hypercoagulable state by reducing natural anticoagulants and increasing procoagulant factors. Such changes are reflected in standard laboratory tests (SLTs). During emergent situations, SLTs often do not reflect the current haemostatic profile due to excessive turnaround time. The Thromboelastograph (TEG® 6S) is capable of assessing coagulation and fibrinolysis rapidly, within 20 minutes, favouring its use in urgent clinical situations including massive haemorrhage during delivery. Manufacturer, reference ranges are provided for all parameters.

Aims: Are reference ranges to represent haemostasis in late pregnancy, both for viscoelastometry and Standard Laboratory tests required and can they be applied to represent the haemostatic profile in a more clinically represntative manner?

Methods: This study was a prospective observational study involving the enrolment of 69 pregnant women near full term attending the elective C-Section clinic at The Rosie Hospital, Cambridge, UK between 8th of February 2021 and 28th of April 2021. All participants were recruited, with full informed consent. The aim of this study was to confirm coagulation changes in late pregnancy and determine pregnancy specific reference ranges for viscoelastic and SLTs using CLSI EP28-A3c.

Results: Although reference ranges of late pregnancy patients were within the reference ranges stated by the manufacturer, the distribution of results differed. All parameters demonstrated a hypercoagulable profile, close to the hypercoagulable extreme of the manufacturer ranges. This reduces the sensitivity of the manufacturer ranges for detecting deviations from baseline. Locally validated reference ranges improve sensitivity to detect risk of bleeding, reflected in abnormal viscoelastic parameters

Conclusion(s): The results observed confirmed the hypercoagulable state experienced during late pregnancy. These results provide additional evidence for the need for establishment of obstetric specific reference ranges on the TEG® 6s point of care analyser.

Image

Distribution of standard laboratory test results in late pregnancy. The overlaid box represents manufacturer recommended reference ranges, not specific to pregnancy. QFA – Quantified Fibrinogen Assay.

Table

Figure 2 – Obstetric specific reference ranges for visoelastometric parameters on the TEG -R- 6S. N/A – Not Applicable, range either not provided or assay not performed on this cartridge. ACT – Activated Clotting Time, A10 – amplitude at 10 mins, CK = Citrated Kaolin TEG ®, CRT = Citrated Rapid TEG ® , CKH = Citrated Kaolin TEG ® with Heparinase, CFF = Citrated TEG® Functional Fibrinogen. A = Parametric Method, B = Robust Method, C = 95th Percentile method

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/validation-of-clinical-reference-ranges-for-viscoelastometric-assessment-of-haemostasis-teg-6s-and-standard-laboratory-tests-in-obstetric-patients/