Would you check ANCA titers in a patient with a history of PR-3-ANCA glomerulonephritis in remission and a stable creatinine but with recurrent microscopic hematuria?

Not sure there is an easy answer to this. A patient in remission should not get a recurrence of glomerular hematuria unless the disease is active. A new onset glomerular hematuria would certainly make me worried about a relapse, some of which may be subtle, indicating "grumbling disease".

The data o...

Absolutely, especially PR3 AAV. I may not act on it alone, but if the PR3 was increasing there is evidence that that (serologic relapse) is a harbinger of clinical relapse. Creatinine climbing is the last thing I would wait to make a decision on. Pr3 AAV is a nasty disease that relapses and I never ...

If you really mean free current hematuria that would indicate that the hematuria is not persistent and certainly you cannot get a recurrence and remission within short periods of time.

Unless the creatinine rises and there is evidence of active disease i.e. proteinuria and hematuria which is persist...

I would only order repeat Titers after remission if there is worsening proteinuria, hematuria or renal function.

Yes. But I would also consider cytologic evaluation, esp if hx of cytoxan use.

If you have the prior serological history and U/A findings, you will be able to classify this patient if he is in remission or relapse, after ruling out other ethologies for hematuria.