A fasting plasma phosphate concentration above 1.5 mmol/l (47 mg/l) in adults indicates hyperphosphatemia. Further classification defines mild to moderate hyperphosphatemia as up to 2.6 mmol/l (80 mg/l) and severe hyperphosphatemia as greater than 3.2 mmol/l (100 mg/l). The most common cause of hyperphosphatemia is renal failure. In analyzing plasma phosphate levels care must be taken to exclude pseudohyperphosphatemia. Spurious levels are produced by paraproteinemias, hyperlipidemia, hemolysis, and hyperbilirubinemia ( L.a..r.n.eL.199.5). Clinically unexplained increases in plasma phosphate levels should initiate a search for potential causes of pseudohyperphosphatemia. Life-threatening hyperphosphatemia is much less common than similarly severe hypophosphatemia, and when it does occur it is usually the result of liberation of intracellular stores ( L„a,u..,..1986).
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