Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1116 page)

   Administration of anabolic steroids, androgens, epinephrine, glucagon, insulin

   Cushing syndrome (some patients)

   Prolonged hypothermia (e.g., open heart surgery)

   TPN with inadequate phosphate supplementation

   Refeeding after prolonged starvation (e.g., anorexia nervosa)

   Thyrotoxic periodic paralysis

   Sepsis

   PTH-producing tumors

   Familial hypocalciuric hypercalcemia

   Severe malnutrition, malabsorption, severe diarrhea

   Often more than one mechanism is operative, usually associated with prior phosphorus depletion.

   Limitations

   Interference may occur with serum samples from patients diagnosed as having plasma cell dyscrasias and lymphoreticular malignancies associated with abnormal Ig synthesis, such as multiple myeloma, Waldenström macroglobulinemia, and heavy chain disease.

   Should be measured in fasting morning specimens because of a diurnal variation. Phosphorus has a very strong biphasic circadian rhythm. Values are lowest in the morning, peak first in the late afternoon, and peak again in the late evening. The second peak is quite elevated, and results may be outside the reference range.