Phosphate is the major intracellular anion in the body and is required for the metabolism of fat, carbohydrate, and protein in oxidative phosphorylation. Low-plasma phosphate levels may not necessarily equate with total body phosphorus deficiency and may be due to a transcellular shift from the extracellular to the intracellular space. Spuriously low phosphate levels may also be seen in patients receiving mannitol therapy and in patients with multiple myeloma, Waldenstrom's macroglobulinemia, and monoclonal gammopathies. Plasma levels may also demonstrate diurnal variations, with the highest levels measured between 2 a.m. and 6 a.m. and the lowest between 8 a.m. and noon, although this may not be evident in patients in the critical care setting. However, clinical features of phosphorus depletion have only been described in the presence of low plasma inorganic phosphate levels, and therefore plasma levels are crucial in diagnostic decision making. Plasma levels should be checked twice a week in critically ill patients (Table,.!).
nimLl rj'i m os-1.5 M Iff &H7 1W< ton <05 <15
Table 1 Plasma phosphate levels
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