ObjectiveTo observe the effect of continuous renal replacement therapy (CRRT) on serum phosphate level in patients after cardiac surgery. MethodA single-center retrospective observational study was conducted on 30 patients received CRRT after cardiac surgery. There were 14 males and 16 females with mean age of 57.0±10.8 years (ranged 37-79 years). A total of 16 patients underwent CRRT with continuous veno-venous hemofiltration (CVVH), and 14 patients with continuous veno-venous hemodiafiltration (CVVHDF). The serum phosphate level was measured before treatment, at 24 h, and 48 h during therapy and 24 h after phosphate salt supplementation. ResultsThe level of serum phosphate at 24 h and 48 h during CRRT was decreased (0.6±0.4 mmol/L vs. 0.4±0.2 mmol/L vs. 1.1±0.3 mmol/L, P<0.01). After intravenous phosphate salt supplementation, serum phosphate level got increased (0.6±0.3 mmol/L, P<0.01). There was no statistical difference in serum phosphate level between CVVH and CVVHDF (P>0.05). ConclusionHypophosphatemia occurs frequently during CRRT, particularly with long treatment time. Phosphate salt supplementation is necessary. The dosage of the supplementation should be adjusted personally based on the regularly monitoring results of serum phosphate tests.