Diabetic ketoacidosis (DKA) is still a major contributor to morbidity and mortality in diabetes. The triad of hyperglycaemia, ketosis and acidosis can be diagnosed within a few minutes of the patient presenting, by measuring blood glucose and ketones using a meter, and venous blood pH on a blood gas analyser. Quantifying ketosis allows accurate distinction between simple hyperglycaemia and metabolic decompensation. We review the management of DKA, and the emerging role of near-patient testing in diagnosing ketosis and monitoring its resolution.