Differential Diagnosis for High Phosphate and High Calcium

Single Most Likely Diagnosis

• Hyperparathyroidism: This condition is characterized by an overproduction of parathyroid hormone (PTH), which leads to increased calcium levels in the blood by stimulating its release from bones and increasing its absorption from the intestine. High phosphate levels can also occur due to decreased excretion of phosphate by the kidneys in response to high PTH levels.

Other Likely Diagnoses

• Malignancy-associated Hypercalcemia: Certain types of cancers, such as multiple myeloma, lung cancer, and breast cancer, can produce substances that mimic the action of PTH or directly cause bone resorption, leading to high calcium levels. Phosphate levels can also be elevated due to tumor lysis syndrome or other metabolic disturbances associated with malignancy.
• Vitamin D Intoxication: Excessive intake of vitamin D can lead to increased absorption of calcium from the intestine and increased bone resorption, causing hypercalcemia. High phosphate levels can also occur due to increased absorption from the intestine.
• Familial Hypocalciuric Hypercalcemia (FHH): This is a rare genetic disorder that affects the calcium-sensing receptor, leading to inappropriate secretion of PTH and subsequent hypercalcemia. Phosphate levels can be elevated due to the effects of PTH on the kidneys.

Do Not Miss Diagnoses

• Primary Hyperparathyroidism due to Parathyroid Carcinoma: Although rare, parathyroid carcinoma can cause severe hypercalcemia and hyperphosphatemia. Early diagnosis is crucial for treatment and prognosis.
• Multiple Myeloma with Renal Failure: In the context of multiple myeloma, renal failure can lead to both hypercalcemia (due to bone resorption) and hyperphosphatemia (due to decreased renal excretion of phosphate).

Rare Diagnoses

• Sarcoidosis: This condition can cause an increase in vitamin D production, leading to increased absorption of calcium from the intestine and subsequent hypercalcemia. Phosphate levels can also be affected.
• Williams Syndrome: A rare genetic disorder that can cause hypercalcemia due to increased sensitivity to vitamin D. Phosphate metabolism can also be altered.
• Jansen's Metaphyseal Chondrodysplasia: A rare genetic disorder characterized by hypercalcemia and phosphate abnormalities due to constitutive activation of the PTH receptor.