Diagnosis of FXIII deficiency: data from multicentre studies amongst UK NEQAS and PRO-RBDD project laboratories

Background: FXIII deficiency is a rare bleeding disorder, and specific FXIII assays are recommended to detect this deficiency. Multicentre UK NEQAS exercises have demonstrated a move from clot solubility screening tests to FXIII assays, improving diagnostic performance. Aims: In this study, we investigated the performance and diagnostic accuracy of FXIII investigations in centres enrolled in the PRORBDD project (prospective data collection on patients with fibrinogen and Factor XIII deficiencies), in comparison to UK NEQAS centres. Methods: Samples from a FXIII deficient subject and a normal donor were sent to 141 UK NEQAS and 29 PRO-RBDD centres, who were asked to perform their routine investigation for FXIII deficiency, and interpret their results. Median, coefficient of variation and range were determined for each assay method.Results: Results were returned from 98 UK NEQAS and 21 PRORBDD centres. 39 UK NEQAS and 11 PRO-RBDD centres reported clot solubility screen results – diagnostic errors were made by one NEQAS centre (false negative for the FXIII deficient sample) and one PRO-RBDD centre (false positive for the normal sample). 66 UK NEQAS centres and 15 PRO-RBDD centres reported FXIII assay results. Medians (range, CV) were as follows: 4.6 l dL 1 (0.0–107.0 l dL 1, 195%) and 3.9 l dL 1 (0.0–11.0 l/dL 1, 69.4%) for the FXIII deficient sample and 108 l dL 1 (15.6–148.0 l dL 1, 15%) and 103 l dL 1 (47.0–127.0 l dL 1, 20.4%) for the normal sample respectively. Diagnostic errors were made by 2 UK NEQAS centres. Conclusion: Approximately 70% of both UK NEQAS and PRORBDD centres now employ FXIII assays, in keeping with international recommendations. However, solubility tests continue to be used. Our data show that this can be successful in some centres, depending on the sensitivity of the method in use. Diagnostic errors are made by centres using both solubility screens and FXIII assays and laboratories should ensure good quality assurance procedures to improve diagnostic accuracy. Disclosure of Interest: None declared.