A pregnant woman in her second trimester has a plasma glucose of 165 mg/dL and is found to have glucosuria despite having a normal renal tubular transport maximum for glucose. Which physiological change best explains her glycosuria?
- A Increased GFR lowers the renal threshold for glucose below the transport maximum predicted value ✓
- B Decreased GFR raises filtered glucose load above the threshold
- C Pregnancy hormones directly inhibit SGLT2 in the proximal tubule
- D Increased plasma volume raises the transport maximum for glucose
Correct answer: A. Increased GFR lowers the renal threshold for glucose below the transport maximum predicted value
Explanation
In pregnancy, GFR rises by up to 50 percent, so the filtered glucose load increases even at a plasma level well below the usual threshold of about 180 mg/dL. Because the transport maximum per nephron does not increase proportionately, the effective renal threshold for glucose falls, and glucosuria can appear at plasma levels of 140 to 160 mg/dL. Direct inhibition of SGLT2 by pregnancy hormones is not a recognized mechanism.
Reference: Guyton and Hall Textbook of Medical Physiology, 14th ed.
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