From Dee McMichael, Blood Bank Supervisor, All Children’s Hospital, St. Petersburg, FL:
I was trying to post a question on your site but each time I received a connection failure. I will follow up with my IT department but thought I might be able to post my question in an email.
(Dee, we apologize for the connection inconvenience, which may be an issue traceable to our service provider. For anyone having difficulty logging in, please email me at [email protected] for follow-up, we can swiftly resolve the issue.)
Dee’s question follows:
A recent CAP survey revealed an inconsistency among laboratories when reporting factor assays in the presence of an inhibitor. In your opinion, what is the highest dilution that should be tested when an inhibitor is suspected? Is it appropriate to report the value of the highest dilution with a comment indicating inhibitor activity? We recently had a patient with a Bethesda titer of 14. Factor VIII results from the regular curve were: 1:10 = 1%; 1:20 = 2%; 1:40 = 4%; 1:80 = 6%; 1:160 = 12%. All values were below the linearity of the curve. From the low curve the value was <1%. In your opinion, what would have been the appropriate value reported: <1%, linearity of the low curve; <7% linearity of the regular curve; or 12%, highest value obtained but extrapolated from the curve? Thank you for your insight.
Dee, when the inhibitor is a lupus anticoagulant, many institutions carry out the dilutions to the point at which two dilutions provide parallel results, then report the parallel result as the factor activity level. Your approach may be a little different when dealing with a factor inhibitor. I’m visiting with Dr. Larry Brace, Edward Hospital (Naperville, IL), who recommends that there is no reason to carry dilutions past the linearity limit. He advises that <7% is an appropriate report. Further, presuming that your patient’s physician is attempting to achieve stable coagulation using large factor VIII concentrate doses, or perhaps a factor VIII bypassing agent such as NovoSeven or FEIBA, your best approach is to test for stability using the PTT and follow with periodic new Bethesda titers. We hope this helps.
By the way, at your convenience, please respond with the specimen number of the CAP survey, as I’d like to follow up this question with comments from some of our CAP experts. Thank you.