The differences in acid-base status and the calcium parathyroid axis between peritoneal dialysis and hemodialysis

Several guidelines have set the target levels of serum Ca, phosphorus, and parathyroid hormone (PTH) for better management of chronic kidney disease-mineral and bone disorders (CKDMBD) in dialysis patients. Although serum ionized Ca (iCa) is a biologically active component, corrected Ca (cCa) is used in clinical settings. However, the association between iCa and cCa is affected by acid-base status. We investigated the difference in acid-base and the calcium-parathyroid status between hemodialysis (HD) and peritoneal dialysis (PD).

The markers associated with CKD-MBD were measured in 142 patients receiving chronic dialysis (69 on PD and 73 on HD).

Serum bicarbonate levels were significantly higher in the PD group than in the HD group (26.6 ± 2.8 vs. 22.9 ± 2.0 mEq/L, p < 0.01). The serum iCa levels and the iCa/cCa ratio were significantly lower in the PD group than in the HD group (iCa 1.07 ± 0.08 vs. 1.14 ± 0.08 mmol/L, p < 0.01; iCa/cCa ratio 45.5 ± 3.1% vs. 49.7 ± 3.2%, p < 0.01). The cCa levels were significantly higher in the PD group than in the HD group (9.4 ± 0.4 vs. 9.1 ± 0.4 mg/dL, p < 0.01). Intact PTH levels were significantly higher in the PD group than in the HD group (220 (40 - 581) vs. 133 (30 - 666) pg/mL, p < 0.01).

We found that PD patients had lower iCa and higher PTH levels despite higher cCa levels as compared to HD patients. These results suggested that the assessment of both Ca and PTH should be different between PD and HD.