The primary cause of hyperphosphatemia is decreased phosphorus excretion because of renal insufficiency or renal failure (acute or chronic). Decreased phosphate excretion also occurs with hypoparathyroidism. Decreased parathyroid activity leads to decreased calcium concentration and increased phosphorus concentration. Increased serum phosphorus absorption may also occur with increased intake of vitamin D or excessive quantities of milk. An increased intake of phosphorus or phosphorus-containing medications, such as enemas, laxatives, or antacids, can cause substantial absorption of phosphorus. Blood transfusions may also cause increased levels of phosphorus because phosphate leaks from the blood cells during storage. Phosphates may be released in excessive quantities in patients who are receiving chemotherapy for neoplastic diseases. Muscle necrosis because of trauma, viral infections, or heat stroke may also cause hyperphosphatemia because muscle tissues store the bulk of soft tissue phosphates.