To the Editor: I read with interest the article by Hu and Isaacson 1 on methods to distinguish type 1 from type 2 diabetes.
While a laboratory workup may be helpful in some hyperglycemic patients, I am unsure what value C-peptide testing (it costs approximately $40 at ARUP Laboratories, Salt Lake City, UT) would offer to the patient in question. Even without considering his age (48), two diabetic parents, and weight of 278 lb, the fact that he had controlled his diabetes for 6 years with diet and metformin makes a history of type 1 diabetes impossible. Could he have new-onset autoimmune diabetes complicating type 2 diabetes? His age makes this highly unlikely, and as the authors note, this is the phase of type 1 diabetes when a C-peptide level may still be normal. My guess is that the level was actually sent just “to see,” or as a rough measure of whether his pancreatitis had so impaired his insulin secretion that he would have an insulin-deficiency diabetes in addition to his type 2 diabetes. One hopes, however, that the severity of pancreatitis would be the primary clue to this possibility.
One test won’t break the camel’s back, but I write to promote the “booger rule” coined by a former mentor: ordering a test is like picking your nose—you have to know what you’re going to do with the result before you go digging. This advice encourages clinical problem-solving and reduces phlebotomy-induced anemia, venous access issues, and costs. (In my academic hospitalist practice, I can frequently cancel hundreds of dollars of “morning labs” on a nightly basis.) In some cases it may be crucial: as resident, I was unable to stop a cardiac catheterization we knew could not influence care, and biopsy of a brain mass in an elderly patient (too ill for any cancer care) that caused a lethal hemorrhage. As an attending, I have prevented a diagnostic colonoscopy on a patient with less than a week to live.