A patient with a plasma glucose of 360 mg/dL has a measured glucose excretion of 100 mg/mL in urine at a flow rate of 2 mL/min. The transport maximum (Tm) for glucose in this patient is most likely which of the following?

• A Plasma glucose is below the renal threshold; Tm is normal
• B Tm cannot be determined without measuring inulin clearance
• C Tm is zero because no glucose is being reabsorbed
• D Glucose is appearing in urine because the filtered load exceeds Tm (splay phenomenon) ✓

Explanation

At plasma glucose of 360 mg/dL, the filtered load (GFR × Pglucose) exceeds the Tm for glucose (~375 mg/min at normal GFR), causing glycosuria. The splay phenomenon means glucose appears in urine before all nepron units reach their individual Tm. Distractor A is wrong because 360 mg/dL exceeds the renal threshold (~180-200 mg/dL). Distractor B is wrong because the concept of Tm does not require inulin measurement to be understood, though clearance would quantify it precisely.

Reference: Boron and Boulpaep Medical Physiology, 3rd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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