Abstract
Introduction: The fractional excretion of sodium (FE Na) in urine has appeared as a helpful way
to distinguish prerenal azotemia from acute tubular necrosis (ATN).
Objectives: The urinary index of sodium has some limits. Lithium can be an additional careful
indicator. The goal of our study was to assess the standards fractional excretion of sodium and
lithium, (FE Na and FE Li) in distinguishing pre-renal azotemia (PRA) from ATN.
Patients and Methods: Twenty-seven patients with prerenal azotemia, 25 patients with ATN and
20 healthy persons were included in this investigation. The plasma and urine sodium, creatinine
and lithium levels were assessed. Additionally, FE Na and FE Li were calculated. To assess the
diagnostic usefulness of FE Na and FE Li in discriminating prerenal azotemia from ATN, we
created a receiver operating characteristic (ROC) curve.
Results: The area under the curves (AUCs) of fractional excretion of Li and Na were 0.84 and
0.83 for distinguishing prerenal azotemia from ATN, respectively. There was a significant direct
association between FE Na and FE Li in patients with ATN (P=0.001). No significant association
of FE Na and FE Li in patients with prerenal azotemia was detected (p=0.26). By a cutoff point of
2.96%, the sensitivity and specificity for FE Na, were 68% and 75%, respectively for distinguishing
PRA from ATN. By a cutoff point of 4.17%, the sensitivity and specificity of FE Li were 80% and
79%, respectively, for distinguishing prerenal azotemia from ATN.
Conclusion: This investigation appeared a high AUC and accuracy of fractional excretion of
sodium and lithium as a diagnostic method for distinguishing prerenal azotemia from ATN
when used simultaneously. However, the discrimination of sensitivity and specificity of fractional
excretion of lithium was greater than the fractional excretion of Na.