Has this happened to you? A negative HLA-B27 test turning positive later or vice versa?
Technically speaking, this can never happen. HLA-b27 is a genetic marker & just like a blood group it can never change. In that case, what can go wrong?
Let us now understand how the HLA-B27 gene is tested.
It is processed using three different methods
- Microlymphocytotoxicity (MLCT)
- Flowcytometry (FC)
- DNA based typing using a Polymerase chain reaction based assays (PCR)
The methods are arranged in the order of their accuracy with PCR based method being the most accurate. A few patients that test negative with Flowcytometry method do turn out to be positive with the PCR method.
Flowcytometry can also give an ‘indeterminate’ (inconclusive) report that needs to be rechecked with a PCR based method. This is how the discrepancy in subsequent tests sets in.
So the next time to get your HLAB27 checked; do have a look at the method as well.
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