Fractional excretion of sodium and potassium and urinary strong ion difference in the evaluation of persistent AKI in sepsis

Objective

To evaluate the diagnostic performance of FENa (Fractional excretion of sodium), FEK (fractional excretion of potassium) and uSID (urinary strong ion difference) in predicting pAKI in sepsis and septic shock.

Design

Retrospective cohort study.

Setting

Two intensive care units in Argentina.

Patients

Adult patients with a confirmed diagnosis of sepsis or septic shock and AKI, and had a urinary biochemistry within 24 h of the AKI diagnosis.

Interventions

None.

Main variables of interest

We evaluated the diagnostic accuracy of FENa, FEK and uSID through a ROC (Receiver Operating Characteristic) curve analysis.

Results

80 patients were included. 40 patients presented pAKI. pAKI group had higher APACHE, SOFA score, and mortality rate. In the ROC curve analysis, uSID had no diagnostic utility (AUC = 0.52, p = 0.69). FENa presented moderate accuracy showing an AUC of 0.71 (95% CI 0.60−0.83; p = 0.001), while FEK presented low accuracy with an AUC of 0.69 (95% CI 0.57−0.80; p = 0.04). The optimal Youden point for identifying pAKI was at a FENa higher than 0.51 % with a specificity of 72.5% and a sensitivity of 65.0%. In the case of FEK, a value higher than 21.9 % presented the best relation, with a specificity of 67.5% and a sensitivity of 65.0%.

Conclusions

urine biochemistry interpretation in septic patients must be revised. FENa and FEK are related to the severity of AKI and could be helpful complementary tools for diagnosing pAKI.