Professional and Linguistic Assessments Board (PLAB) Practice Exam

What laboratory findings are indicative of osteomalacia?

1. High calcium, low phosphate

2. Normal calcium, normal phosphate, high alk phos

3. Low calcium, low phosphate, high alk phos

4. High phosphate, low calcium

The correct answer is: Low calcium, low phosphate, high alk phos

In the context of osteomalacia, the laboratory findings typically show low levels of both calcium and phosphate, alongside elevated alkaline phosphatase. This combination occurs because osteomalacia is associated with defective mineralization of bone due to insufficient levels of vitamin D or phosphate, leading to an imbalance in the mineral content of the bone matrix. Specifically, low calcium suggests hypocalcemia, which can occur when there is inadequate absorption of calcium or its loss from the bones. Low phosphate levels indicate a deficiency in phosphate, which is critical for bone mineralization. The elevated alkaline phosphatase level reflects increased osteoblastic activity as the body attempts to compensate for the poor mineralization, signaling ongoing bone remodeling. Other scenarios, such as high calcium with low phosphate, normal ranges of calcium and phosphate with high alkaline phosphatase, or high phosphate with low calcium, are not typically reflective of osteomalacia and can point to other metabolic bone diseases or disorders. These conditions demonstrate different underlying physiological processes that distinguish them from osteomalacia.