The association of normal-range serum phosphorus with immunoglobulin A nephropathy progression: a retrospective cohort study.

PURPOSE

The relationship between serum phosphorus and immunoglobulin A (IgA) nephropathy progression remains uncertain, especially normal-range serum phosphorus. Therefore, we herein examined the relationship between the normal-range serum phosphorus and the progression of IgA nephropathy.

METHODS

One hundred sixty-two patients with primary IgA nephropathy were divided into three groups according to tertiles of baseline serum phosphorus (first tertile: 0.73-1.04 mmol/L; second tertile: 1.04-1.21 mmol/L; third tertile: 1.21-1.60 mmol/L). Estimated glomerular filtration rate (eGFR) was calculated using the chronic kidney disease epidemiology collaboration. The composite outcome was defined as a decrease of at least 50% in eGFR from baseline or end-stage kidney disease (ESKD). The association of serum phosphorus with IgA nephropathy progression was estimated using Cox proportional hazards models, adjusting for potential confounders.

RESULTS

During a median 16 month follow-up period, 15 patients reached a composite outcome. In the crude Cox proportional hazard model, baseline serum phosphorus as a continuous variable was associated with increased risk for adverse renal outcomes [hazard ratio (HR) = 63.510, 95% confidence interval (CI) = 3.953-1020.284, P = 0.003], and the high tertile of serum phosphorus group had an increased risk of the composite outcome by using the low tertile group as the reference (HR = 11.895, 95% CI = 1.522-92.993, P = 0.018). After adjustment for traditional risk factors, the high tertile of serum phosphorus group was significantly related to IgA nephropathy progression compared with the low tertile group (HR = 9.424, 95% CI = 1.019-87.165, P = 0.048).

CONCLUSIONS

Relatively higher serum phosphorus levels within the normal range were significantly associated with the progression of IgA nephropathy.