Acute Hemolytic Reactions
LAB DIAGNOSIS, PART 2: If one or more of the screening tests mentioned on the previous page make you suspect acute hemolysis, or if you have other reason to suspect that hemolysis may be going on, some confirmatory tests may be in order.
Repeat ABO/Rh, Screen, and Crossmatch
Since over 80% of acute HTRs result from ABO incompatibility, rechecking the patient's basic testing on both the post transfusion and pretransfusion samples may reveal an error in typing. The error may have occurred anywhere in the process. If an ABO error occurred, repeating the crossmatch may reveal incompatibility which was missed either due to sample error or technical error. Non-ABO reactions, on the other hand, may sometimes be confirmed by finding an antibody on a repeat antibody screen that was missed before, again with possibilities including sample error and technical error, as well as a weak antibody that failed to show its ugly head the first time around (that last mechanism is much more common with delayed HTRs than with acute HTRs, by the way).
Indirect Bilirubin Increase
I'm not a big fan of using indirect bilirubin in the initial workup of an acute HTR, but the test does have some value in confirming the diagnosis. Indirect bili will usually increase significantly over the first few hours of acute hemolysis, then start to go down again by 10 or 12 hours. This test is far more useful in acute HTRs caused by antibodies other than ABO, because rising indirect bilirubin is better associated with extravascular hemolysis (ABO HTRs are usually intravascular).
Urine Check for Hemoglobinuria
Again, I'm not a big fan of this test. Some Blood Bank physicians recommend routine urinalysis for every suspected transfusion reaction, but I don't believe this adds anything that you don't already know by examining a fresh sample for visible hemoglobinemia.
Haptoglobin
OK, here's the part where I get to talk about a test that everyone thinks they need to know about, but that I simply do not use. I get asked about haptoglobin's value in working up an acute HTR all the time, and my answer is this: "I scoff at the inanity of your question!" Well, honestly, I don't usually say that (mostly because I'm not sure what "inanity" actually means!), but I truly don't believe haptoglobin is very useful. Everyone knows that haptoglobin scavenges free hemoglobin, and as such, should decrease in the setting of an intravascular hemolytic episode. The problems that I have with haptoglobin are these: First, it is not a "stat" test. In most places, it takes long enough to get the result back that you already know whether or not the patient has acute hemolysis by the time you get the test back! Second, and more critically, I don't like the way people try to use the test. Simply checking an isolated posttransfusion haptoglobin is of minimal value to me, because it's just a snapshot in time. The only way haptoglobin is of use, in my opinion, is if you see a significant (ie, >50%) decrease in haptoglobin from the pretransfusion value. So, if you must use haptoglobin, I believe you must check not only the fresh sample but also the pretransfusion sample.
FORWARD to Pathophysiology
BACK to Diagnosis part 1
Back to Acute Hemolytic Reactions
Back to Transfusion Reaction Types