Hematuria refers to the presence of blood in the urine, as defined as more than 5 to 10 red blood cells per high-power field (RBC/hpf). A urine dipstick analysis is a highly sensitive measure for detection of blood, but it lacks specificity. This translates into a large number of false positives, in which case, the urine dipstick is positive, but microscopy reveals fewer than 5 to 10 RBC/hpf. This particular combination can be seen in the following benign or pathologic circumstances:
1. Ingestion of certain foods: beets, blackberries, food coloring
2. Ingestion of certain medications: chloroquine, ibuprofen, iron, sorbitol, nitrofurantoin, phenazopyridine, urates or rifampin (which often produces orange urine)
3. Hemoglobinuria: often in the setting of hemolytic anemia
4. Myoglobinuria: related to muscle damage (rhabdomyolysis), often after vigorous exercise or trauma
5. Urinary tract infection: secondary to the action of bacterial peroxidases on the dipstick
6. Delay in reading urine dipstick after submersion in urine
Given the large number of situations in which a positive dipstick may not represent true hematuria, all urine samples that test positive on dipstick analysis must be sent for microscopy to confirm hematuria. This applies in the setting of gross hematuria (where the urine may appear red, pink, amber, tea-colored, or brown) or with routine dipstick screening at well-child examinations.