Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (238 page)

   Hematuria is common and, in many patients, particularly young adults, is transient and inconsequential. With increasing age, common causes can include inflammation or infection of the prostate or bladder and calculi. In patients over age 35, hematuria is associated with a higher risk of benign prostatic hyperplasia and renal or GU malignancies.

   Patients on oral anticoagulants and those with a high international normalized ratio (INR) are at higher risk of hematuria. Even if present in such patients, it is necessary to investigate for alternative source(s) of the condition.

   Isolated hematuria occurs in patients with calculi, trauma, prostatitis, sickle cell trait or disease, tuberculosis, and
Schistosoma haematobium
infection. Acute cystitis or urethritis in women can cause gross hematuria. Hypercalciuria and hyperuricosuria are also risk factors for unexplained isolated hematuria.

   
Benign familial
or
recurrent hematuria
refers to asymptomatic, recurrent hematuria without proteinuria or other laboratory abnormalities. Persistent or recurrent hematuria, even if only microscopic, should be investigated, especially in patients over age 50. Other family members may be affected. The condition may clear spontaneously.

   Laboratory Findings

   The single most important test in the evaluation of hematuria is the microscopic analysis of urine sediment, which can often distinguish glomerular from nonglomerular bleeding.

   Microscopy of centrifuged urinary sediment should be examined under high dry magnification. Note that <3% of normal persons have ≥3 RBC per HPF. RBCs or casts indicate that the blood is of glomerular origin. The most common causes of isolated glomerular hematuria are IgA nephropathy, hereditary nephritis (Alport syndrome), and thin basement membrane disease. The presence of clots rules out a glomerular origin—large thick clots suggest a bladder origin, whereas small stringy clots indicate upper urinary tract disease. The presence of WBCs suggests inflammation or infection.

   The urine dipstick can detect RBCs at a level equivalent to one to two RBCs per HPF, but results in more false-positive tests owing to a number of interfering factors (listed below), and so a positive dipstick test must be confirmed by microscopic examination of the urine. Proteinuria is also detected by dipstick, and a 2+ proteinuria in the presence of microscopic hematuria indicates glomerular disease.

   Immunocytochemical staining for human Tamm-Horsfall protein is positive with >80% of RBCs of renal origin and <13.1% of RBCs of nonrenal origin.

   Imaging studies, urinary cytology, cystoscopy, or occasionally renal biopsy may be indicated in cases of persistent hematuria with no obvious etiology.

   Limitations on the Urine Dipstick Test

   Causes of false-positive results