Hyperphosphatemia in kidney transplant recipients (KTRs) is known to predict a graft and patient survival in several studies. However, studies concerned with hypophosphatemia are scarce. To evaluate the impact of serum phosphorus level on patient and graft survival, we performed a retrospective multi-center cohort study. A total of 2786 KTRs were classified into seven groups according to serum phosphorus level at 1 year after transplantation with intervals of 0.5 mg/dL (lowest group, <2.5 mg/dL; highest group, ≥5.0 mg/dL; reference group, 3.5-3.99 mg/dL). The Cox model was adjusted with age, gender, donor type, age of donor, diabetes mellitus, and eGFR at 1 year after transplantation. The mean age of the recipients was 41.7±11.4 years, and 59.3% were male. Both of lowest group and highest group were significantly associated with patient mortality compared to reference group (Hazard ratio [HR] 4.164, 95% confidence interval [CI] 1.310-13.231, P=0.016 vs. HR 5.149, CI 1.671-15.869, P=0.004, respectively). Graft loss was also higher in both of lowest group and highest group compared to reference group (HR 2.799, CI 1.235-6.345, P=0.014 vs. HR 2.746, CI 1.387-5.433, P=0.004, respectively) (Figure 1), even though eGFR was not different between lowest group and reference group (65.4±19.3 vs. 61.9±16.7 mL/min, P=0.334).The levels of serum calcium (lowest, reference, and highest group; 10.0±0.9 vs. 9.3±0.5 vs. 9.2±0.5 mg/dL, P<0.001) and parathyroid hormone (246.3±211.9 vs. 64.0±46.9 vs. 76.3±129.6 pg/mL, P<0.001) were higher in lowest group compared to other groups. In conclusion, Serum phosphorus at 1 year after transplantation has U-shape association with graft failure and mortality in KTRs.

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