Internal Medicine

0521779407-09 CUNY1086/Karliner 0 521 77940 7 June 13, 2007 7:54

Hypophosphatemia 795

tests

■Low serum phosphorus does not necessarily indicate total body

depletion as only 1% of body phosphorus is in blood.

■Basic blood tests: Serum phosphorus: (moderate=serum phosph

<2.5 mg/dl; severe <1.0 mg/dl)

■Basic urine tests: Diagnosis based on history, trend in phosphorus

values and blood pH (to distinguish acute shift), and urine phos-

phorus (<100 mg/day=GI loss or shift)

■Other tests: If urine phosphorus >100 mg/day, measure 24-h urine

for glucose, amino acids for Fanconi’s syndrome, and serum calcium

(high in primary hyperparathyroidism, low in vitamin D-resistant

rickets)

differential diagnosis

■Hypophosphatemia occurs because of 1) decreased intestinal

absorption, 2) increased urinary losses, and/or 3) extracellular to

intracellular shift. Severe hypophosphatemia is usually due to com-

bination of factors.

■Decreased intestinal absorption: antacid abuse, malabsorption,

chronic diarrhea, vitamin D deficiency, starvation, anorexia, alco-

holism

■Increased urinary losses: primary hyperparathyroidism, post renal

transplant, extracellular fluid volume expansion, glucosuria (after

treating DKA), post obstructive or resolving ATN diuresis, aceta-

zolamide, Fanconi’s syndrome, X-linked and vitamin D-dependent

rickets, oncogenic osteomalacia due to circulating phosphatonins

■Redistribution: respiratory alkalosis, alcohol withdrawal, severe

burns, TPN, recovery from malnutrition when inadequate phosph is

provided (post feeding syndrome), leukemic blast crisis

management

What to Do First

■Assess severity and symptoms so as not to overtreat hypophos-

phatemia due to cellular shifts.

General Measures

■If possible, treat orally to avoid metastatic calcification.

specific therapy

■Indications: Only treat symptomatic severe hypophosphatemia with

intravenous agents. Otherwise choose oral agent. Phosph comes as