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Cord Blood PTT

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.

Comments (2)
Bleeding Disorders
Mar 1, 2021 4:25pm

Over the years our Special
Over the years our Special Coagulation department has tested a number of cord blood specimens for Factor 8 (VIII) one stage clot based test. To date the testing on the child’s status always been accurate on the cord blood.

Feb 15, 2021 4:53pm

This is a timely question and
This is a timely question and we are not sure about the next steps in our system. We did not validate cord blood as a source for coag testing. Our main specialist does agree that cord blood is not an ideal specimen, but apparently the national hemophilia groups all recommend testing off the cord for babies to save them from the trauma of a needle stick (I have not verified this statement) and thus other providers in his group support testing cord blood. Our in-house factor VIII and IX are plasma activity assays determined by performing a modified aPTT assay. We also have a chromogenic FVIII validated. Is cord blood considered equivalent to peripheral blood, or are there additional validations necessary to allow this source? Is it better to allow testing on cord blood and leave it up to the provider to determine validity of results, or refuse to test and require a peripheral stick or send the sample to another lab? Thanks!

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