thorough investigation of previous medical and surgical conditions, presence of
hypertension, recent infections and use of medications with potential nephrotoxic
side effects. Examination of the child should be focused on the identification of
hypovolemic states, generalized edema, measurement of the blood pressure and
skin inspection to identify palpable (vasculitis) and non-palpable purpuric lesions
(hemolytic-uremic syndrome).
Abdominal examination and auscultation often reveal renal artery stenosis and
the presence of a pelvic mass responsible for obstructive renal failure.
Laboratory findings
- Urinary osmolality
In pre-renal failure, the avid absorption of sodium to maximize water
retention leads to a concentrated urine. Urine osmolality can reach very
high levels.
In renal/parenchymal failure, the inability to concentrate urine leads to
diluted urine with osmolality levels of less than 300 mOsm/L. - Urinary sodium
Measurements of urinary sodium help differentiate if the failure is pre-renal
or renal. In low flow states, the kidneys attempt to save sodium and water
to expand the intravascular volume; therefore the urinary sodium is low
(less than 20 mEq/L).
In renal/parenchymal failure, the kidney has lost its absorptive ability and
is unable to retain sodium; therefore the urinary sodium is high (greater
than 30-40 mEq/L). - Fractional excretion of sodium