The relationship between phosphorus level and peak oxygen uptake in hemodialysis patients awaiting renal transplantation

Background & aim: End-stage renal disease (ESRD) is one of the most common diseases, which affects many aspects of patients’ lives. By improving these aspects, disabling factors can be overcome. The measurement of exercise capacity through peak oxygen uptake is an important factor in predicting mortality and survival in patients with ESRD after transplantation. Decrease in amount of maximal oxygen uptake (VO2 max) is directly associated with post-transplant mortality. In these patients, hyperphosphatemia is a concomitant disease related to secondary hyperparathyroidism leading to ESRD. In the current study, we aimed to examine the relationship between phosphorus level and VO2 uptake in renal transplant candidates receiving hemodialysis therapy. Material and methods: In total, 30 renal transplant candidates under hemodialysis were evaluated through spirometry and exercise test. Then, the results ere registered according to the inclusion criteria comprising of age, gender, and phosphorus level. The obtained data were analyzed through statistical and analytical measures. Results: All the cases were male with the mean age of 37.93±10.48 years (age range: 20-55 years) and mean VO2 max of 23.46±8.22 ml/kg/min (range: 6.88-43.44 ml/kg/min). In these patients, the mean phosphorus level was 6±2.3 mg/dL (range: 2-10.6 mg/dL) and eight patients had high levels of phosphorus (more than 5.5 mg/dL). Both groups showed normal (≥20 ml/kg/min) and abnormal (20˃ ml/kg/min) rates of VO2. T-test showed a significant relationship between phosphorus level and VO2 max, such that in patients with low phosphorus level there was an abnormal VO2 max (P=0.027); in this regard, Pearson correlation test also demonstrated a direct correlation (r=0.538, P=0.002). Furthermore, Fisher’s exact test reflected a significant association between high level of phosphorus and normal VO2 max (P=0.029). Conclusion: In ESRD patients waiting for renal transplantation, Decreased blood phosphorus is a predisposing factor for decreased exercise capacity, and hypophosphatemia may lower VO2 max through reducing energy of skeletal muscles. Knowing the relationship between phosphorus level and VO2 max can help lower the rate of mortality in patients with ESRD waiting for renal transplantation. However, treatment modalities reducing serum levels of phosphorus should be used with caution in these patients.