Clinical Evaluation of the Child with Hematuria

Chapter 503 Clinical Evaluation of the Child with Hematuria

Hematuria is defined as the presence of at least 5 red blood cells (RBCs) per microliter of urine and occurs with a prevalence of 0.5-2.0% among school-aged children. Quantitative studies demonstrate that normal children can excrete more than 500,000 RBCs per 12-hr period; this increases with fever and/or exercise. In the clinical setting, qualitative estimates are provided by a urinary dipstick that uses a very sensitive peroxidase chemical reaction between hemoglobin (or myoglobin) and a colorimetric chemical indicator impregnated on the dipstick. Chemstrip (Boehringer Mannheim), a common commercially available dipstick, is capable of detecting 3-5 RBCs/µL of unspun urine; significant hematuria is suggested by >50 RBCs/µL. False-negative results can occur in the presence of formalin (used as a urine preservative) or high urinary concentrations of ascorbic acid (i.e., in patients with vitamin C intake >2000 mg/ day). False-positive results may be seen in a child with an alkaline urine (pH > 9), or more commonly following contamination with oxidizing agents such as hydrogen peroxide used to clean the perineum before obtaining a specimen. Microscopic analysis of 10-15 mL of freshly centrifuged urine is essential in confirming the presence of RBCs suggested by a positive dipstick.

Red urine without RBCs is seen in a number of conditions (Table 503-1). Heme-positive urine without RBCs is caused by the presence of either hemoglobin or myoglobin. Hemoglobinuria without hematuria can occur in the presence of hemolysis. Myoglobinuria without hematuria occurs in the presence of rhabdomyolysis resulting from skeletal muscle injury and is generally associated with a 5-fold increase in the plasma concentration of creatine kinase. Rhabdomyolysis can occur secondary to viral myositis, crush injury, severe electrolyte abnormalities (hypernatremia, hypophosphatemia), hypotension, disseminated intravascular coagulation, toxins (drugs, venom), metabolic disorders of muscles, and prolonged seizures. Heme-negative urine can appear red, cola colored, or burgundy, owing to ingestion of various drugs, foods (blackberries, beets), or food dyes, whereas dark brown (or black) urine can result from various urinary metabolites.

Evaluation of the child with hematuria begins with a careful history, physical examination, and urinalysis. This information is used to determine the level of hematuria (upper vs lower urinary tract) and to determine the urgency of the evaluation based on symptomatology. Special consideration needs to be given to family history, identification of anatomic abnormalities and malformation syndromes, presence of gross hematuria, and manifestations of hypertension, edema, or heart failure.

Causes of hematuria are listed in Table 503-2. Upper urinary tract sources of hematuria originate within the nephron (glomerulus, convoluted or collecting tubules, and interstitium). Lower urinary tract sources of hematuria originate from the pelvocalyceal system, ureter, bladder, or urethra. Hematuria from within the glomerulus is often associated with brown, cola or tea-colored, or burgundy urine, proteinuria >100 mg/dL via dipstick, urinary microscopic findings of RBC casts, and deformed urinary RBCs (particularly acanthocytes). Hematuria originating within the convoluted or collecting tubules may be associated with the presence of leukocytes or renal tubular epithelial cell casts. Lower urinary tract sources of hematuria may be associated with gross hematuria that is bright red or pink, terminal hematuria (gross hematuria occurring at the end of the urine stream), blood clots, normal urinary RBC morphology, and minimal proteinuria on dipstick (<100 mg/dL).

Table 503-2 CAUSES OF HEMATURIA IN CHILDREN

UPPER URINARY TRACT DISEASE