From Ann Helen: Can you trust results of PTT and factor VIII in umbilical cord blood? It seems as if it is usual to draw umbilical cord blood from newborns when the mother is a known carrier of Hemophilia A. Can you trust a high APTT and a low factor VIII in such a sample? Kind regards.
Thanks for your question. You can trust a low one-stage clot-based factor VIII activity level and a low chromogenic factor VIII level in cord blood, as factor VIII levels in newborns are roughly equivalent to adult factor VIII levels. However, the PTT [APTT] is likely to be prolonged in response to low activity levels of liver-sourced intrinsic factors such as factor IX. There may be some value in performing a von Willebrand factor antigen level and expressing factor VIII activity as a FVIII/VWFAg ratio.
If you are testing a prenatal or neonatal specimen for the diagnosis of hemophilia A [FVIII deficiency] or hemophilia B [FIX deficience], next-generation sequencing is now preferred over phenotypic testing, keeping in mind that 30% of hemophilia A cases arise as new mutations. Further, the factor IX activity level in cord blood may not be diagnostic, as factor IX levels in neonates do not reach adult levels in the first months of life.
See Napolitano M, Kessler CM. Hemophilia A and hemophilia B. In Kitchens CS, Kessler CM, Konkle BA, Streiff MB, Garcia DA. Consultative Hemostasis and Thrombosis Fourth Edition, Elsevier, 2019; see also Fritsma GA. Hemorrhagic disorders and laboratory assessment. In Keohane EM, Otto CN, Walenga JM. Rodak’s Hematology: Clinical Practice and Applications Sixth Edition, Elsevier, 2020.