I had a recent communication through the American Society for Clinical Laboratory Science Consumer Forum in which a patient with severe chronic bleeding symptoms had been diagnosed as having both a factor VIII and a factor XIII deficiency. Given prevalence data, I compute the odds of this combination as 1 in 10 billion, and have found no published cases, though I found two cases of combined von Willebrand disease and factor XIII deficiency. I suggested the factor XIII deficiency conclusion could be false, based on a false positive urea solubility assay. It struck me that factor VIII deficiency would generate a weak clot that would dissolve in the urea solution, giving the false impression of a factor XIII deficiency, but I can’t find anything in writing to support my conclusion. I recommended the patient’s physician ensure the lab was using one of the updatedchromogenic factor XIII assays. Do you have any experience with a combined VIII and XIII deficiency? Also, would you please comment on the urea solubility test?