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Potassium | Sodium | Chloride | Calcium | Magnesium | Serum CO2

Most of the phosphorus in the body is part of organic compounds. The serum phosphorus measured is the free portion (15% of total body phosphorus is in serum as a salt). The organic phosphorus compounds are in phospholipids in cell membranes, bone, ATP and enzymes. The inorganic phosphorus we measure is involved in nerve transmission and acid-base management.

Phosphorus is absorbed very efficiently in the small intestine. Phosphorus levels are controlled by calcium metabolism parathormone, renal excretion and intestinal absorption. Because an inverse relationship exists between serum calcium and phosphorus, calcium metabolism affects phosphorus levels. Vitamin D and parathormone weakly stimulate phosphorus absorption. H

Normal levels:  Adults     3.0-4.5 mg/dl
                          Elderly:   slightly lower than adult
                          Neonate: 43.-9.3 mg/dl
                          Child:      4.5-6.5 mg/dl
                          Hemolysis causes false elevation

Hypophosphatemia

Signs and symptoms:

• Depressed WBC function
• Bleeding
• Bone demineralization
• Hemolytic anemias
• Nausea & vomiting
• Decreased O₂ release to tissue (shifts oxyhemoglobin dissociation curve to left)

Causes:

• Chronic antacid ingestion
• Hyperparathyroidism - Increases urinary excretion
• Hypercalcemia
• Chronic alcoholism - hypomagnesemia, malnutrition
• Vitamin D deficiency
• Treatment of hyperglycemia - insulin drives P into cells
• Alkalosis - causes intracellular shift
• Gram-negative sepsis
• Diabetic ketoacidosis
• Refeeding syndrome - malnourished patients started on hyperalimentation use all available phosphorus in rebuilding, repairing tissue, increased metabolism

Treatment: Increased dietary intake, oral supplementation, IV potassium phosphate

Hyperphosphatemia

Signs and symptoms:

• Tachycardia
• Nausea and diarrhea
• Abdominal cramps
• Muscle weakness
• Flaccid paralysis
• Increased deep tendon reflexes

Causes:

• Hypoparathyroidism
• Renal failure - decreased excretion
• Increased dietary or IV intake
• Acromegaly - increased renal absorption
• Bone metastasis - bone stores mobilized
• Sarcoidosis - increased intestinal absorption due to increased vitamin D production
• Hypocalcemia
• Acidosis - phosphate enters serum to maintain buffer
• Rhabdomyolysis
• Advanced lymphoma or myeloma
• Hemolytic anemia

Treatment:  Dietary restriction
                   Aluminum-containing antacids
                   Hydration
                   Correction of hypocalcemia