Thursday, June 14, 2012

Hematuria in children ( part 5)


Laboratory Studies
The laboratory tests ordered for the evaluation of hematuria must be based on the clinical history and the physical examination. Identification of a glomerular and extraglomerular etiology of hematuria based on a good history and urine examination can help the physician to avoid requesting tests that may be unnecessary.

1- Urinalysis
o    Confirming that a child with red-colored urine has hematuria is mandatory. Dip strip analysis is critically important in patients with dark or abnormal-appearing urine because several substances may discolor the urine and give the appearance of hematuria. The urine dipstick test is currently one of the most useful and sensitive tools in detecting hematuria. This test is based on the peroxidase activity of hemoglobin. It can detect trace amounts of hemoglobin (rather than the presence of RBCs) and myoglobin. False-positive results can occur (certain dyes or drugs, beets, oxalates). Briefly dip the strip in the urine, tap off excess urine, and read the strip at the recommended time (usually 1 min). Dipsticks have a sensitivity of 100% and a specificity of 99% in detecting 1-5 RBCs per high-power field (hpf).
o    The presence of hematuria is most important to confirm, since both normal and abnormal causes (eg, hemoglobinuria, myoglobinuria) can produce false-positive results. Confirmation requires a microscopic examination of the urine for the presence of RBCs and casts. A freshly voided urine specimen should be used. A 10- to 15-mL aliquot of the urine is spun in a centrifuge at 1500 rpm for about 5 minutes. The supernatant is decanted, and the sediment is resuspended in the remaining liquid. The urine sample is then carefully examined under high-power magnification. All noncellular and cellular elements should be noted and recorded. More than 5 RBCs per hpf is generally considered abnormal. RBC casts indicate a glomerulotubular source of hematuria. The absence of RBCs and RBC casts despite a positive dipstick test suggests hemoglobinuria or myoglobinuria.
o    Other cellular elements in the urinary sediment (eg, WBCs, WBC casts) suggest a diagnosis of urinary tract infection. In this latter instance, a urine culture must be performed to determine the causative organism. Crystals, bacteria, protozoa, and other elements may also be seen.
o    Parents of children with isolated microscopic hematuria should be reassured that sufficient time remains to plan a stepwise evaluation. Other investigations should be avoided, and the dipstick and microscopic urinalysis should be repeated twice within 2 weeks (see new guidline).
·         Phase contrast microscopy: A careful examination of the urine for the presence of a significant number of dysmorphic RBCs suggests a renal (glomerular) source of the hematuria. A urine sample that predominantly contains eumorphic RBCs suggests an extrarenal (nonglomerular) source. This test has been reported to have a sensitivity of 83-95% and a specificity of 81-95%. The sensitivity and specificity may vary from one examiner to another.

2- BUN/serum creatinine: Elevated levels of BUN and creatinine suggest significant renal disease as the cause of hematuria.

3- Hematologic and coagulation studies: CBC counts and, sometimes, platelet counts may be performed in selected patients with a clear history of a bleeding disorder. In general, coagulation studies and CBC counts often do not add additional information in the evaluation of hematuria. In certain populations, a sickle cell preparation or a hemoglobin electrophoresis may be useful in establishing the diagnosis of sickle cell disease or trait.

4- Urine calcium: Hypercalciuria is a relatively common finding in children. Measurement of the urine calcium excretion using either a timed 24-hour urine collection for calcium or a spot urine calcium-creatinine ratio can be helpful in establishing hypercalciuria as a cause of hematuria. A calcium excretion of more than 4 mg/kg/d or a urine calcium-creatinine ratio of more than 0.21 are considered abnormal.

5- Serologic testing: Measuring serum complement levels is important if a glomerular cause of hematuria is suspected. Low serum complement levels are seen in postinfectious glomerulonephritis, systemic lupus erythematosus nephritis, bacterial endocarditis, and membranoproliferative glomerulonephritis. A high antistreptolysin (ASO) titer suggests a recent streptococcal infection. Anti-DNase B levels are also indicative of a recent group B streptococcal infection and may be positive even when the ASO level is normal. This latter statement is relevant in poststreptococcal glomerulonephritis secondary to a skin infection. Antinuclear antibody (ANA) titers and the measurement of double-stranded DNA (dsDNA) levels are most helpful in children with suspected systemic lupus erythematosus nephritis.

6- Urine culture: A midstream or clean-catch specimen of urine should be obtained for culture sensitivity whenever a urinary tract infection is suspected. This is especially important in younger children, in whom classical symptoms of a urinary tract infection may be absent.

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