Calcium and Parathyroid USMLE Step 1 Practice Question
A 67-year-old man presents with a 9-month history of progressive lower back pain and gait disturbance. He reports that his hat size has increased over the past year and he has noticed new-onset hearing loss. Vital signs are within normal limits. Physical examination reveals bowing of the left tibia and point tenderness over the lumbar spine. Serum alkaline phosphatase is elevated at 420 U/L (normal <104). X-ray of the lumbosacral spine shows a coarse trabecular pattern with cortical thickening of the L3 vertebra, producing a "picture-frame" appearance. The vertebra is enlarged compared to adjacent vertebrae. Which of the following sets of laboratory findings would best support the suspected diagnosis?
Answer choices
- ASerum calcium 10.8 mg/dL, phosphate 3.2 mg/dL, alkaline phosphatase 420 U/L, PTH 45 pg/mL
- BSerum calcium 11.5 mg/dL, phosphate 2.1 mg/dL, alkaline phosphatase 420 U/L, PTH 125 pg/mL
- CSerum calcium 9.8 mg/dL, phosphate 3.5 mg/dL, alkaline phosphatase 420 U/L, PTH 42 pg/mLCorrect answer
- DSerum calcium 8.2 mg/dL, phosphate 2.8 mg/dL, alkaline phosphatase 420 U/L, PTH 185 pg/mL
- ESerum calcium 11.2 mg/dL, phosphate 4.2 mg/dL, alkaline phosphatase 180 U/L, PTH 18 pg/mL
- FSerum calcium 9.5 mg/dL, phosphate 3.8 mg/dL, alkaline phosphatase 85 U/L, PTH 48 pg/mL
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