Hypophosphatemia
Hypophosphatemia is plasma phosphorus concentration below the normal range (~0.8-1.45mmol/L or 2.4-4.5mg/dL). The low serum concentration reflects a deficit in body phosphorus content and is accompanied by bone mineral loss.
Clinical Findings
As a result of persistent hypophosphatemia, rickets develop predominantly in children and osteomalacia in adults. Further symptoms are short stature and leg deformities.
Pathogenesis
Hypophosphatemia can be caused by an acute shift of extracellular phosphate into the cell, decreased intestinal absorption, and increased urinary excretion. Internal redistribution can be induced by increased insulin secretion, particularly during refeeding and glucose or fructose infusion, acute respiratory alkalosis, and hungry bone syndrome. Intestinal net absorption is disturbed when antacids containing aluminium or magnesium are administered, in short bowel syndrome, low dietary intake, and vitamin D deficiency or resistance. Renal excretion may be increased for acquired or genetic reasons. The acquired forms are due to hyperparathyroidism, vitamin D deficiency, oncogenic factors, osmotic diuresis, and fluid overload. Primary, genetic reasons for increased renal phosphate excretion include x-chromosomal and autosomal dominant hypophosphatemic rickets, vitamin D resistance, and Fanconi syndrome (i.e. Dent disease).
Physiology
Staging
In adults, the normal range of serum phosphate concentration is between 0.84-1.45mmol/l (2.6-4.5mg/dl). Hypophosphatemia is usually asymptomatic if not below 0.64mmol/l (2mg/dl). A severe hypophosphatemia occurs when serum concentration drops below 0.32mmol/l (1mg/dl). It becomes life threatening at 0,16mmol/l (0,5mg/dl).
