HISTORY. Generally, patients with increased serum phosphorus levels exhibit signs and symptoms associated with hypocalcemia. Ask about a current history of chronic laxative or enema use, excess antacid use, and increased intake of foods containing large amounts of phosphorus (dried beans and peas, eggs, fish, meats, milk, nuts). Note if the patient has been admitted for massive burns or trauma, acute pancreatitis, acute or chronic renal failure, neoplastic disorders, or hypoparathyroidism.

Tetany, a condition that leads to increased neural excitability, may develop. Determine if the patient has experienced tingling in the fingertips or around the mouth. As tetany progresses, tingling may progress up the limbs and around the face and increase in intensity from tingling to numbness followed by pain accompanied by muscle spasm. Tetany is more common in patients who have taken an increased phosphorus load by diet or through medication. It is less likely in the renal patient because calcium ionization is increased in the presence of acidosis.

PHYSICAL EXAMINATION. An elevated serum phosphorus level causes few signs or symptoms. Long-term consequences may involve soft tissue calcification for the patient with chronic renal failure resulting from precipitation of calcium phosphates in nonosseous sites, often the kidney, liver, and lungs. Other nonosseous sites may include arteries, joints, skin, or the corneas. Tetany may account for the majority of signs and symptoms because of hypocalcemia. Check for Trousseau's (development of carpal spasm when a blood pressure cuff is inflated above systolic pressure for 3 minutes) and Chvostek's (twitching facial muscles when the facial nerve is tapped anterior to the ear) signs.

PSYCHOSOCIAL. Hyperphosphatemia is most often associated with other chronic problems, such as renal failure, hypoparathyroidism, or chemotherapy for neoplastic diseases. Assess the patient's ability to cope with a serious disease and evaluate the patient's social network for available support and coping abilities.

Diagnostic Highlights


Normal Result

Abnormality with Condition


Serum phosphorus

2.5-4.5 mg/dL

>4.5 mg/dL (adults); >5.5 mg/dL (children)

Reflects phosphorus excess

Serum calcium

8.6-10.3 mg/dL

<8.5 mg/dL

Reflects calcium deficit

Serum ionized calcium (free calcium)

4.5-5.1 mg/dL

<4.5 mg/dL

Reflects ionized calcium (46%-50% of circulating calcium)

Other Tests: Electrocardiogram (ECG), blood urea nitrogen, creatinine

464 Hyperphosphatemia

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