In what may be a first for the Federal Drug Administration, the agency has sent a letter to the makers of an iPhone medical app asking why its approval wasn't sought before release. The uChek app analyzes photos of urine samples to give users quick health information. On Tuesday, the FDA told developer Biosense that it had 30 days to either show the agency that it has already received its blessing, or explain why the app didn't need it in the first place.

UChek — which also runs on the iPad and iPod touch — keys off chemical strips to determine the levels of various elements in a user's urine. For example, a diabetic may use the app to check their blood sugar. In its letter, the FDA doesn't question whether or not the app works as advertised. Instead, the FDA argues that the strips uChek is designed to work with are meant to by read by the human eye. When the uChek app scans the strips, it becomes part of what the FDA describes as an "automated strip reader." Essentially, the agency argues that the app turns the iPhone into a part of a medical testing system that requires its approval. Despite the FDA scrutiny, uChek remains available for download in Apple's iTunes App Store; Biosense told Bloomberg that it plans on getting the app approved by the FDA.