Clinical characteristics and preliminary discriminatory value of low triiodothyronine syndrome in patients with peritoneal dialysis-associated peritonitis

This study aimed to examine the clinical characteristics and preliminarily evaluate the discriminatory value of low triiodothyronine (T3) syndrome in patients with peritoneal dialysis-associated peritonitis (PDAP). Patients admitted for PDAP between January 2020 and May 2022 were categorized into a tested group and an untested group based on whether thyroid function testing was performed at peritonitis onset. The tested group was further subdivided into a low T3 syndrome subgroup and a normal thyroid function subgroup for comparative analysis of clinical characteristics. Correlations between free triiodothyronine (FT3) and other indicators were analyzed. The preliminary diagnostic discriminative value of PDAP complicated by low T3 syndrome was then assessed. Among 181 PDAP patients, 11 were excluded for not meeting the criteria, resulting in 69 patients in the tested group and 101 in the untested group. Baseline characteristics were comparable between the 2 groups, except for the proportion of refractory peritonitis. In the tested group, 26 were in the low T3 syndrome subgroup and 43 in the normal thyroid function subgroup. Compared to the normal group, the low T3 syndrome group had significantly higher levels of WBC, neutrophil count, PCT, and CRP, as well as a higher proportion of refractory peritonitis (all P <  .05). FT3 at peritonitis onset was positively correlated with baseline FT3 but negatively correlated with WBC, neutrophil count, PCT, CRP, and NLR (all P <  .05). Multivariate analysis showed baseline FT3 and WBC remained as factors independently associated with FT3 levels at peritonitis onset ( B  = 0.410, 95% CI 0.214–0.605 and B  = −0.055, 95% CI −0.084 to −0.026, both P  < .001). Compared to combinations involving PCT or CRP, baseline FT3 combined with WBC, neutrophil count, or NLR demonstrated numerically higher AUC values for PDAP patients with low T3 syndrome, specifically 0.750, 0.744, and 0.721 ( P  < .05). PDAP patients complicated by low T3 syndrome exhibited elevated levels of inflammatory markers and a higher proportion of refractory peritonitis. Baseline FT3 and WBC were independently associated with FT3 levels at peritonitis. The combination of baseline FT3 and inflammatory markers showed preliminary discriminatory value for identifying low T3 syndrome in patients with PDAP.