Fractional excretion of sodium or FENa refers to the fraction of filtrated
sodium that is excreted by the kidney. In pre-renal failure, FENa is less
than 1% as the kidney is trying to conserve as much sodium as possible.
In renal conditions, FENa levels are above 2%.
Calculation of FENa:
FENa = Urine [Na] / Plasma [Na] X 100
Urine [Cr] / Plasma [Cr]
A simple microscopic analysis of the urine will help identify several causes
of intrarenal failure by revealing the presence of tubular casts, which are
absent in the normal urine. Hematuria, pyuria and the presence of
eosinophils in urine are indicative of specific conditions.
Epithelial casts are characteristic of ATN and are due to “shedding” of
epithelial cells after tubular injury.
White blood cell and eosinophil casts are representative of AIN,
pigmented casts are typical of myoglobinuria and red blood cell casts are
characteristic of glomerunephritis.
Serum creatinine is a valuable and consistent biochemical marker of renal
function.
Serum creatinine levels are similar to those of the mother in the immediate
neonatal period decreasing by 50% in the first week and reaching normal
levels by the second month of life (0.40 mg/dL). [24] Normal adult levels
are reached during adolescence (1- 1.5 mg/dL). [25]
Preterm infants do not show this pattern of creatinine production and an
