Hematuria

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Hematuria is the presence of blood in a person’s urine. It can be visible, meaning the urine is red, called gross or macroscopic hematuria, or it can be nonvisible, or microscopic. Macroscopic hematuria can be striking and has been documented since ancient times, especially when it appears without a prior event such as trauma, painful urination (dysuria) due to a bladder infection, or flank pain from a kidney stone. Microscopic hematuria may go undetected for years and is only found when a urine analysis is done for other reasons or during a routine exam. The American Urologic Society notes a prevalence of microhematuria between 2.1 to 31.4% of the population. When evaluating hematuria, a consideration of both the patient and the geographic area is warranted. For example, in northern Africa, where the parasite Schistosoma haematobium is endemic, hematuria may be a manifestation of bladder infestation.

The causes of hematuria differ between women and men and so the evaluation, accordingly, should reflect that difference. Bladder and kidney cancer can cause both macro and microscopic hematuria, but the incidence of these cancers differ between the sexes. Men have more than double the incidence of these cancers, but often the evaluation of hematuria is delayed in women (because it can be wrongly attributed to a gynecologic source), so women often have a worse outcome, especially for bladder cancer. Detection of hematuria starts with a dipstick evaluation of the urine. When the stick is dipped in urine, hemoglobin or myoglobin (a muscle protein) will cause a chemical reaction with the compound on the stick, turning the stick blue. False positive results can be caused by consuming beets, rhubarb, azo dye (often used in medications to relieve dysuria), and sulfonamides (sulfa antibiotics). A false positive may also result following a vigorous workout that causes muscle soreness. The muscles release myoglobin into the blood following heavy exercise. False negative results can be caused by high levels of ascorbic acid (vitamin C) in the urine.

When the dipstick shows positive for blood in the urine, examination of the urine under a microscope is imperative. Microscopic examination looks for not just red blood cells, but whether or not those cells are intact or damaged or fragmented, and also white blood cells (suggestive of infection), crystals (suggestive of kidney stones), and casts, which are clumps of cells or protein that would suggest kidney disease. Before running any tests, a thorough patient history and examination must be performed, including smoking history (bladder and kidney cancers are strongly linked to smoking). Initial testing includes a full blood test which evaluates kidney function. Follow up after initial exam may include urine cytology (looks for malignant cells), CT scans, cystoscopy, and referral to a specialist.

Because microscopic hematuria may go unnoticed for years, it is important for everyone to have an annual exam that includes, among other things, a urine analysis.

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