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Bethesda Titer Formula

Two messages from Beaumont on Bethesda titer calculation:

Hi George,

I wanted to ask you if you know the formula to calculate the amount of factor inhibitor BU for the classical Bethesda assay.  We have been graphing the results on the log log paper.  We are working on a new LIS system and would like to program a formula to calculate the result.  I would appreciate any help you could give us.

Karri Henderson MT(ASCP)
Beaumont Laboratory
Coagulation, Assistant Supervisor
Clinical Pathology, Royal Oak


We at William Beaumont Hospital, are installing new software for the lab.  Is there a formula for calculating the Bethesda inhibitor titer?  Currently our techs graph the results by hand. Thank you,

Diane Farrah, BA, BS, MT
William Beaumont Hospital
Royal Oak, Michigan

(See Laura Taylor’s comment added 2/26/2010)

Hi, Karri and Diane,

I’m traveling and away from all my references until Monday. I don’t have enough confidence in my math skills to post a Bethesda titer formula from memory. However, to try for a timely answer, I’m posting this and also forwarding to my colleagues at University of Alabama at Birmingham special coagulation lab to invite them to post an answer. If we don’t get anything before Monday, I will get back to you then. Geo.

Form my colleague Laura Taylor at UAB 2/26/2010:

Hey George!
At UAB, we graph and figure the titer by hand. I guess we’re kind of old fashioned around here. Thanks! Laura

Laura J Taylor, MT (ASCP)
Special Coagulation Laboratory
University of Alabama at Birmingham Hospital

Comments (4)
Feb 21, 2011 7:12am

In Oxford (UK) we use….

(Log(100/%res) / Log 2)) x Dil
In Oxford (UK) we use….

(Log(100/%res) / Log 2)) x Dil (eg 4, if you were using the %res from 1/4 dil..)

Mar 7, 2010 1:55pm

From Dr. Larry Brace, Edward Hospital, Naperville, IL

From Dr. Larry Brace, Edward Hospital, Naperville, IL

Hi, George. At University of Illinois Hospital we send our Bethesda titer samples to Esoterix Coagulation, both against human and porcine factor VIII (or any factor for that matter).  Meanwhile, we use an efficient shortcut. While we did not make this part of the patient record, we diluted the patient sample in our normal plasma pool to give the clinicians an idea of whether they were looking at a high titer inhibitor or a low titer inhibitor.  For example, if 1 part of patient plasma in 19 parts of normal plasma still prolonged the normal plasma PTT, a high titer inhibitor was likely.  The clinicians were satisfied with this information; in fact, this approach was discussed with and approved by our heme/onc group. Of course, we would post the Bethesda titer result as soon as it came back from the reference lab. Rarely did the lab results change the therapy. I hope this helps.

Mar 4, 2010 5:39am

Hi All. We run residual VIII levels and use the age old for
Hi All. We run residual VIII levels and use the age old formula based on the definition of what 1 BU is, that amount of inhibitor that will inacitvate 50% of VIII. We have a chart where we can look up what Bethesda titer corresponds to the residual VIII that we calculate. Clear as mud? If anyone is interested I would be willing to email our procedure. But as far as a formula, you may be able to program you LIS to calculate based on the residual VIII but that is way beyond me!!

Mar 3, 2010 1:22pm

And more from my colleague Dr. Larry Brace at Edward Hospita
And more from my colleague Dr. Larry Brace at Edward Hospital, Naperville, IL. Sorry, George, we don’t have a formula. In fact, when I directed the laboratory at University of Illinois at Chicago we didn’t have one there, either.

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