A 27-year-old woman complains of pain in her left shin. X-rays of the leg reveal a stress fracture of the tibia, decreased cortical bone density, and increased radiolucency. She is suspected of having osteomalacia (impaired mineralization of bone matrix). Which of the following is the most common biochemical manifestation of osteomalacia?

Vitamin D levels are decreased in osteomalacia. In severe osteomalacia, there is bowing of the long bones, inward deformity of the long bones, and wide osteoid borders on bone surfaces. Hypocalcemia is characteristic of osteomalacia; however, secondary hyperparathyroidism often raises the serum calcium to low normal levels. The PTH-mediated increase in phosphate clearance often produces hypophosphatemia.