Hypophosphatemia causes muscle weakness, particularly respiratory muscles.

The problem with being presented with a low serum phosphate result, is that it tells you little about the overall state of intracellular phosphate, and therefore whether total body phosphate depletion exists.

In general, muscles do not function well in hypophosphatemic states. This relates to the importance of phosphate as the body’s source of chemical energy. Hypophosphatemia causes weakness of respiratory muscles, particularly the diaphragm, and causes a leftward shift of the oxyhemoglobin dissociation curve (increasing the tendency for hemoglobin to cling onto oxygen). Patients who are hypophosphatemic may be slow to wean from mechanical ventilation (Agusti, AG; Hypophosphatemia; CCM 1984) (Aubier, M; Hypophosphatemia; NEJM 1985). As one would expect, hypophosphatemia causes skeletal muscle weakness, which may mimic a myopathy. In addition, low serum phosphate my interfere with blood cell function and cause increased red cell fragility.

Hypophosphatemia may cause myocardial dysfunction (Zazzo JF ICM 1995; hypophosphatemia), and may make the myocytes less sensitive to the stimulatory effects of catecholamines. This effect is reversible. Other complications of hypophosphatemia are listed in the table below.

Clinical Manifestations of Hypophosphatemia