Blood Glucose After a Meal in a Patient
A 45-year-old patient has fasting blood glucose of 7.8 mmol/L (normal 3.9–5.5) on two occasions. After a 75 g oral glucose load, glucose rises to 14.2 mmol/L at 2 hours and remains at 11.0 mmol/L at 3 hours. Plasma insulin is elevated at baseline and rises further after the load, but the rise is sluggish. The patient is overweight and reports frequent thirst and urination. A urine dipstick shows glucose but no ketones. The patient's brother has type 1 diabetes.
1. Distinguish between type 1 and type 2 diabetes in this patient using the clinical and laboratory data. What does the presence of glucose but absence of ketones in urine suggest?
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The data favor type 2 diabetes. Fasting glucose ≥7.0 mmol/L on two occasions and 2-hour post-load glucose ≥11.1 mmol/L meet diagnostic thresholds. Type 1 diabetes results from autoimmune β-cell destruction, so insulin would be low or undetectable and ketones likely present because unchecked lipolysis produces ketone bodies. Here insulin is elevated - indicating insulin resistance with compensatory hypersecretion - and the sluggish rise suggests β-cell dysfunction on top of resistance. The absence of ketones argues against absolute insulin deficiency: enough insulin remains to suppress ketogenesis. Obesity, age, and the gradual onset fit type 2. The brother's type 1 is a distractor; family history of type 2 would be more relevant. The thirst and urination reflect osmotic diuresis once glucose exceeds the renal threshold (~10 mmol/L).
2. Explain the physiological mechanism linking the patient's overweight state to the observed insulin pattern, and predict what a euglycemic clamp or HOMA-IR would show.
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Excess adipose tissue, especially visceral, releases free fatty acids and inflammatory cytokines that impair insulin signaling in muscle, liver, and fat - insulin resistance. Pancreatic β-cells compensate by secreting more insulin, producing the elevated baseline and post-load insulin. Over time, chronic demand leads to β-cell exhaustion, so the post-load rise becomes sluggish despite high levels. A HOMA-IR calculation (fasting insulin × fasting glucose / 22.5) would be elevated, confirming resistance. A euglycemic clamp would show a reduced glucose infusion rate needed to maintain euglycemia - the gold-standard measure of resistance. The combination of high insulin with high glucose is the signature: if insulin were low, the diagnosis would shift toward type 1 or late-stage β-cell failure.