Highlighting Levels of Indoxyl Sulphate among Critically Ill Patients with Acute Nephrotoxicity; Correlations Between Indoxyl Sulphate Levels and Patients' Characteristics

Abstract

Background: Many animal studies suggested that the uremic toxin indoxyl sulphate can add to renal damage following induced nephrotoxicity and this effect has not been proved in patients with such complication.

Methods: This is a prospective, case-control, and an observational study conducted on 74 critically ill patients with acute nephrotoxicity. It was designed to measure serum levels of indoxyl sulphate on the day of enrollment and over the course of their illness using high performance liquid chromatography (HPLC-UV) and to test the correlation between these levels and patient's demographics, clinical characteristics, physiological variables, and their outcomes.

Results: Critically ill patients with acute nephrotoxicity had significantly higher total (tIS) and free (fIS) indoxyl sulphate than healthy controls and significantly lower than patients with end-stage renal disease (ESRD). Although, no correlation was found between tIS or fIS and mortality, among survivors, tIS, fIS, creatinine and eGFR were independently associated with no renal recovery.

Conclusion: Serum indoxyl sulphate levels were elevated in critically ill patients with acute nephrotoxicity. There is an association between high levels of indoxyl sulphate and no renal-recovery outcome among survivors of acute nephrotoxicity. Early removal of indoxyl sulphate from patients' blood may improve their outcomes.

Keywords: HPLC; Indoxyl sulphate; Mortality; Prognosis; Toxic acute kidney injury.

Fig. 1

HPLC chromatogram of pooled normal serum spiked with 200 µmol/l 3-indoxyl sulphate potassium salt in methanol buffer (peak 1) and internal standard (peak 2). Under these conditions, tIS was eluted at ∼ 4.45 minutes, fIS at ∼ 4.5 minutes and the internal standard at ∼ 6 minutes. (N.B. These are mean elution times for total and free IS, as not all samples were analyzed in the same day).

Fig. 2

Flow chart of outcomes at hospital discharge and three months of follow up.

Fig. 3

Comparison of basal serum total indoxyl sulphate (tIS) concentrations (A) and basal serum free indoxyl sulphate (fIS) concentrations (B) among the three studied groups. Data were analyzed using Kruskal-Wallis test between the all groups: p value is significant at< 0.05, and Klomogorov-Simirnov test between groups (I versus II) and (I versus III): p value is significant at< 0.05.

Fig. 4

Basal serum total indoxyl sulphate (tIS) (A) and basal serum free indoxyl sulphate (fIS) (B) concentrations among patients with toxic AKI according to need for renal replacement therapy (RRT). Bars and error bars represent median and range for each group. Data were analyzed using Mann-Whitney test; p value is significant at< 0.05.

Fig. 5

Basal serum total indoxyl sulphate (tIS) (A) and basal serum free indoxyl sulphate (fIS) concentrations (B) among patients with toxic AKI according to RIFLE classes. Bars and error bars represent median and range for each stage. Data were analyzed using Kruskal-Wallis test; P value is significant at< 0.05.

Fig. 6

Basal serum total indoxyl sulphate (tIS) (A) and basal serum free indoxyl sulphate (fIS) (B) concentrations among patients with toxic AKI according to the nephrotoxin type. Bars represent range with line at median for each nephrotoxin. Data were analyzed using Kruskal-Wallis test; P value is significant at< 0.05.

Fig. 7

Receiver-operating characteristics (ROC) curve of weight for comparison of the performance of eGFR, creatinine, free IS and total IS in prediction of no-recovery among survivors of toxic AKI patients. The cut-off values were defined by calculating Youden index scores and were chosen as the closest scores to 1.

Fig. 8

Receiver-operating characteristics (ROC) curve of weight for comparison of models in prediction of no-recovery among survivors of patients with toxic AKI. Model 1= creatinine + eGFR, AUC= 0.7785 Model 2= creatinine + eGFR + tIS, AUC= 0.7937 Model 3= creatinine + eGFR + fIS, AUC= 0.7778 Model 4= creatinine + eGFR + tIS + fIS, AUC= 0.8399