A 34-year-old woman comes to the office due to diarrhea, weight loss, and fatigue over the past year. The diarrhea occurs 2 or 3 times daily and is accompanied by crampy abdominal pain. She has diarrhea occasionally at night but no tenesmus or blood in the stool. The patient describes her stools as very foul smelling and floating. Associated symptoms include diffuse bone pain. Physical examination is unremarkable. Laboratory results show hemoglobin of 9.8 g/dL with a mean corpuscular volume of 72 µm³. Which of the following serum laboratory findings would be expected in this patient?

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11ec25c8_d0c8_cc93_bc81_2dccc0fda762_MD0003_00 This patient has chronic diarrhea and abdominal pain; the associated weight loss and steatorrhea (ie, foul-smelling, greasy, or floating stools) suggest a malabsorptive disorder, most likely celiac disease (CD) (ie, immune-mediated hypersensitivity to gluten). CD causes villous atrophy in the small bowel, reducing its absorptive capacity. CD is often complicated by nutritional deficiencies due to inadequate absorption. In particular, malabsorption of iron is common and leads to iron deficiency (microcytic) anemia, as in this patient. Deficiencies of fat-soluble vitamins (eg, A, D, E, K) are also common. 1,25-dihydroxyvitamin D (calcitriol, the active form of vitamin D) is required for optimal intestinal absorption of calcium and phosphorus. In vitamin D deficiency, absorption of calcium is impaired, which stimulates secretion of parathyroid hormone (PTH) (ie, secondary hyperparathyroidism). PTH causes release of calcium from bone, increases renal calcium reabsorption, and suppresses renal phosphate reabsorption. Circulating calcium is restored to normal or mildly low levels, but phosphate levels are significantly reduced. In the bone, vitamin D deficiency can lead to osteomalacia (ie, abnormal mineralization with bone pain) and osteoporosis (ie, decreased bone density). 1,25-dihydroxyvitamin D (Choice B) In some patients with malabsorption due to CD, calcium may be restored to normal, but this requires elevated levels of PTH (ie, PTH would not be low). (Choice C) Hypoparathyroidism is characterized by hypocalcemia, hyperphosphatemia, and low PTH; it is most often a complication of thyroid surgery with inadvertent damage to the parathyroid glands. Symptoms are primarily related to hypocalcemia (eg, paresthesia, muscle cramps). Malabsorptive syndromes are typically associated with secondary hyperparathyroidism, not hypoparathyroidism. (Choice D) 25-hydroxyvitamin D is converted to 1,25-dihydroxyvitamin D by 1-alpha-hydroxylase in the kidneys. In patients with chronic kidney disease (CKD), production of 1,25-dihydroxyvitamin D is reduced, leading to hypocalcemia and secondary hyperparathyroidism. However, unlike in CD and other malabsorptive disorders, serum phosphate is elevated due to decreased renal phosphate clearance. (Choice E) Primary hyperparathyroidism (eg, PTH-secreting parathyroid adenoma) would lead to high PTH, hypercalcemia, and hypophosphatemia. Calcium is not elevated in patients with secondary hyperparathyroidism due to malabsorption. Educational objective: Celiac disease (ie, immune-mediated hypersensitivity to gluten) commonly presents with diarrhea, abdominal pain, and weight loss. The associated villous atrophy leads to malabsorption, causing fat-soluble vitamin (eg, A, D, E, K) deficiencies and iron deficiency anemia. Vitamin D deficiency can lead to hypocalcemia, hypophosphatemia, and secondary hyperparathyroidism. References: Hypocalcemia: updates in diagnosis and management for primary care. (http://www.ncbi.nlm.nih.gov/pubmed/22439169)

A 34-Year-Old Woman Comes to the Office Due to Diarrhea