Hypophosphatemia caused by renal
phosphate loss occurs frequently after
kidney transplantation. In assumption of systemic
phosphorus depletion, the presumed deficit commonly is replaced by oral
phosphate supplements. However, such treatment is debatable, because intracellular
phosphorus stores have not been assessed in this setting and may not be accurately reflected by serum
phosphate concentrations. Moreover, disturbances in
mineral metabolism from
chronic renal failure, such as
hypocalcemia and
hyperparathyroidism, may be prolonged with oral
phosphate supplements. Conversely, a neutral
phosphate salt might improve renal
acid excretion and systemic
acid/base homeostasis for its properties as a urinary
buffer and a poorly reabsorbable
anion. Twenty-eight patients with mild early posttransplantation
hypophosphatemia (0.3-0.75 mmol/L) were randomly assigned to receive either neutral
sodium phosphate (Na(2)HPO(4)) or
sodium chloride (NaCl) for 12 weeks and examined with regard to (1) correction of serum
phosphate concentration and urinary
phosphate handling; (2) muscular
phosphate content; (3) serum
calcium and
parathyroid hormone (PTH); and, (4) renal
acid handling and systemic
acid/base homeostasis. Mean serum
phosphate concentrations were similar and normal in both groups after 12 weeks of treatment; however, more patients in the NaCl group remained hypophosphatemic (93% versus 67%). Total muscular
phosphorus content did not correlate with serum
phosphate concentrations and was 25% below normophosphatemic controls but was completely restored after 12 weeks with and without
phosphate supplementation. However, the percentage of the energy-rich
phosphorus compound
adenosine triphosphate (
ATP) was significantly higher in the Na(2)HPO(4) group, as was the relative content of phosphodiesters. Also, compensated
metabolic acidosis (hypobicarbonatemia with respiratory stimulation) was detected in most patients, which was significantly improved by neutral
phosphate supplements through increased urinary titratable acidity. These benefits of added
phosphate intake were not associated with any adverse effects on serum
calcium and PTH concentrations. In conclusion, oral supplementation with a neutral
phosphate salt effectively corrects posttransplantation
hypophosphatemia, increases muscular
ATP and phosphodiester content without affecting
mineral metabolism, and improves renal
acid excretion and systemic
acid/base status.