Imagine a 29 year old type I diabetic and who's still using 70/30 insulin in the post-Ultralente Lantus era because he can't afford the latter. So, when WalMarts runs out of 70/30, he tries to get by with regular insulin, and lo and behold a week later he's in the ER in DKA (diabetic ketoacidosis).
If you're a perspicacious doctor familiar with the treatment of low income diabetics, this case is not a great mystery. Insulin non-compliance eventuating in DKA. Easily treated with fluids and reinstitution of insulin. The case may be slightly more difficult if it were a female with pyelonephritis, slightly more with shock and MSOF, and maybe totally different if it were a 59 year old male with a stroke or an MI and MOSF and DKA in an inscrutible and tangled causal web.