I'd say that is a little bit cavalier. I don't know that there has been a study determining the WBC level which indicates systemic infection, but urologists are taught that a WBC count >15,000 should raise a concern for pyelonephritis. In the setting of an obstructing stone pyelonephritis is a surgical emergency. Now, will there be some patients with obstructed pyelo and a normal white count? Sure. And, do some patients with a WBC of 18,000 just have a severe reactive leukocytosis? Sure. But, I think this is similar to the idea that surgeons should be taking out a few normal appendixes to be on the safe side. The natural history of an obstructed pyelonephritis is worsening septic shock and then death, so the stakes are pretty high.
This is directly from the 2008 AUA Update, "Management of the Acute Stone Event":
So I would say that it is certainly the standard care, at least among urologists, to do a laboratory evaluation and to consider intervention in a patient with obstructing calculus and leukocytosis. If you are going to send the patient home without me being involved, do whatever you want. If you are going to consult me or even curbside me over the phone, I am going to recommend labs.
This is the AUA recommended algorithm for assessment and management of the acute stone episode from the same paper if anyone is interested:
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