Routine laboratory tests cannot be used to confirm factor XIII deficiency because none of them test clot stability.18 Specific investigations are needed, divided into screening tests, functional assays and immunological assays.
The most common screening test assesses clot stability. If the sample clot breaks down within a few hours, the patient likely is suffering from severe factor XIII deficiency, provided that fibrinogen levels are normal. If factor XIII is present in the sample, the clot remains stable after 24 hours.18 Notably, only very low levels of factor XIII are required for the clot to stabilize – a fibrin meshwork is possible when factor XIII is present at 1–3% of normal levels.19 Factor XIII deficiency is confirmed using an assay capable of measuring factor XIII levels.
Two commercially available assays measure factor XIII levels indirectly by monitoring the level of specific chemicals (ammonia or synthetic amine) involved in the cross-linking process responsible for factor XIII-mediated clot stability:18-19
The presence of factor XIII in plasma can also be measured directly using an enzyme-linked immunosorbent assay (ELISA).19
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