Pediatric emergency medicine trisk 2887 2887
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hypocalcemia, and/or hyperphosphatemia depending on the degree of
dysfunction and the chronicity of the underlying etiology. Serial assessment
of renal function and electrolytes will be required to determine the disease
course and to monitor for the development of electrolyte derangements and
changes in renal function. Although the results may not affect the course of
management within the ED, laboratory studies aimed at assessing for an
underlying cause may assist specialists with treatment in a more rapid
fashion. In cases of suspected glomerulonephritis, serum complement
studies, serologic testing for streptococcal infection, and autoimmune
antibodies such as antinuclear, anti-DNA, antineutrophil cytoplasmic, and
antiglomerular basement (anti-GBM) antibodies may be considered in
conjunction with specialist consultation.
Initial urine studies should include urinalysis with microscopic
assessment. An elevated urine specific gravity may be consistent with
prerenal physiology. The presence of nitrite or leukocyte esterase suggests a
urinary tract infection. Detection of large heme by dipstick is found in
glomerulonephritis and myoglobinuria, and differentiation between these
two disorders relies upon the presence or absence of red blood cells in the
urine sediment, respectively. Heavy proteinuria by dipstick, which detects
albumin excretion, would be suggestive of glomerular disease and should
be followed by a quantitative urine protein to creatinine ratio (normal less
than 0.2, nephrotic range greater than 2 to 3). Microscopic examination of
the urine sediment may be normal or nearly normal, consistent with
prerenal AKI and some cases of acute tubular necrosis (ATN). ATN may
also be associated with granular, muddy brown, and/or tubuloepithelial cell
casts. The finding of red blood cell casts is pathognomonic of
glomerulonephritis, and concomitant white blood cells or white blood cell
casts would be consistent with an exudative nephritis such as postinfectious
glomerulonephritis or renal vasculitis. Urine sediment associated with acute
interstitial nephritis (AIN) varies and includes microscopic hematuria,
sterile pyuria, and white blood cell casts. The degree of proteinuria
associated with AIN is also variable, though is typically not severe except
in nonsteroidal anti-inflammatory drug (NSAIDS)-induced AIN, which
may be associated with nephrotic range proteinuria. If interstitial nephritis
is suspected, the urine should be evaluated for the presence of eosinophils,
though sensitivity and specificity of urine eosinophilia is limited.
