Febrile Nonhemolytic Reactions
The problem with diagnosing an FNH is not that it's hard (because it isn't); it's that it's just really unsatisfying!
Invariably, when you go through your workup and find absolutely positively nothing, it leaves you with the feeling that you have accomplished exactly that: Absolutely positively nothing!
As you've probably guessed by now, FNH is a diagnosis of exclusion, which means that once you've ruled out everything really interesting and dangerous, you're left with (drum roll, please)... an FNH.
To be specific, in your screening workup, the paperwork check is negative, the check for visible hemolysis is negative, and the DAT is negative...usually! (That is just a little reward for those of you who kept reading after that horrendously dry first paragraph!) Remember, about 15-25% of hospitalized patients have positive DATs that are NOT associated with clinical disease (or, for our purposes, with hemolytic transfusion reactions). When the DAT comes up positive on a reaction workup, I generally want to know if that positivity is a change for that patient, so I'll ask the Blood Bank to run a DAT on the pretransfusion sample and compare. In most cases, the difference is negligible or explainable, so you can go on with your life, but in case of a significant change, the patient should really be evaluated closely.
Now is where it starts to get interesting (to me, at least!). Let's talk about why these reactions occur.
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