Factor XIII - an under diagnosed deficiency - are we using the right assays?

The clot solubility test is the most widely used method for detection of factor (F)XIII deficiency. However, it will only detect severe deficiencies; consequently mild deficiencies and heterozygous states are probably under diagnosed. Objective: As an alternative first-line screening test, we assessed an automated quantitative ammonia release assay (QARA). Patients/methods: Inter-assay imprecision was evaluated with commercial normal and pathological control plasmas (10 replicates on each of 5 days). Using the QARA and other commercial assays a comparative assessment of congenital (FXIII range <1-70 u dL ¹, n = 9) and acquired (n = 43) deficiencies was made. We also investigated the prevalence of acquired deficiencies in hospitalized patients using residual samples from adult patients (n = 1004) and from a paediatric intensive care unit (ICU, n = 56). Results: Assay imprecision was acceptably low (normal control: mean 86.6 u dL ¹; cv = 2.0%; pathological control: mean 27.5 u dL ¹; cv = 3.8%). Using an iodoacetamide blanking procedure, the QARA results (FXIII range <1-70 u dL ¹) exhibited close agreement with those from an immuno-turbidometric FXIII A-subunit (FXIII-A) method. There was also good correlation (R² 0.89) between the QARA (range 20-180 u dL ¹), a second chromogenic assay, the FXIII-A and FXIII A+B-subunit ELISA. We found that 21% of samples from adult patients had FXIII levels <70 u dL ¹ (mean normal ± 2 SD 73-161 u dL ¹) with 6% <50 u dL ¹. Within the paediatric ICU samples, 52% were <70 u dL ¹, with 21% <50 u dL ¹. Conclusions: Our data demonstrates that the automated assay is sensitive, highly reproducible and the results from clinical samples suggest that acquired FXIII deficiency is a relatively common phenomenon in hospital patients after surgery and in ICU.