INTRODUCTION — Exercise is one of the many causes of hematuria (increased red blood cells excretion in the urine) (figure 1). Exercise-induced hematuria can be defined as gross or microscopic hematuria that occurs after strenuous exercise and resolves with rest in individuals with no apparent underlying kidney or urinary tract pathology .
Issues related to exercise-induced hematuria in otherwise healthy individuals will be reviewed here. Exercise may also worsen hematuria in patients with underlying glomerular disease, such as IgA nephropathy [2,3].
The general evaluation of adults or children with hematuria is discussed separately:
ETIOLOGY AND PATHOGENESIS — Hematuria has been described after a variety of forms of exercise [1,4,5]. These include contact sports, such as football and boxing, and noncontact sports, such as long-distance (marathon or endurance) running [6-8], rowing, and swimming. Hematuria appears to be rare with cycling but has been described, even with stationary bike riding (eg, spinning) [9,10].
The frequency with which hematuria occurs with long-distance running was evaluated in a study of 45 male and female participants who competed in an ultra long-distance marathon . After the race, 11 (24 percent) had hematuria. The hematuria disappeared within seven days. A similar incidence (18 percent) was noted in a report of 50 marathon runners who did not have hematuria on prerace samples obtained daily for three days .
The rate of increased red cell excretion after long-distance running is higher when defined by more sensitive testing. This was illustrated in a report of 48 participants in a long-distance race . The urinary red cell count increased in 44 and to values above the normal range (8000/mL in centrifuged urine) in 33 (69 percent). These changes would not usually be detectable in routine practice since only five tested positive for blood on the urine dipstick.
Traumatic — Direct trauma to the kidneys and/or bladder may be responsible for the hematuria associated with contact sports such as football and boxing. In addition, trauma to the bladder may occur with long-distance running and rarely with cycling due to the up and down movement of the bladder [6,7,9]. Ecchymoses and frank contusions have been noted on cystoscopy after long-distance running, possibly due to repeated impact of the flaccid wall of the bladder against the bladder base [7,9]. A possible exacerbating factor is a near empty bladder, which increases the likelihood of apposition of the surfaces of the bladder . Bicycling-related hematuria is attributed to the vigorous and repeated collisions of the perineum with the saddle during acrobatic or bumpy rides (bicycle-seat hematuria) . Urinary symptoms associated with bicycle riding exist also in female bicyclists . Among 282 female members of a bicycling club, one third experienced perineal trauma, 19 percent of which were associated with hematuria and dysuria, and 34 percent with perineal numbness. The frequency and the severity of symptoms were related to bicycling exposure as measured in cycling hours and miles . In some cases of cycling-related hematuria, stopping cycling or adjusting the saddle position prevented recurrence [14,15].
The study of 48 participants in a long-distance race cited above used phase contrast microscopy, which is more sensitive than standard microscopy. This study found dysmorphic red cells in all runners, red cell casts in 10, and new proteinuria in 18, all of which are indicative of glomerular bleeding (picture 1A-C) . Most  but not all  other studies have also found dysmorphic red cells with exercise-induced hematuria. (See "Etiology and evaluation of hematuria in adults", section on 'Red cell morphology'.)
Nontraumatic — Hematuria can occur with participation in noncontact sports such as rowing, swimming, and stationary bike riding (eg, spinning) [1,4,5,10]. Several mechanisms have been proposed in these cases but none has been proved . One such mechanism is kidney ischemia due to shunting of blood to exercising muscles [1,5]. Another proposed mechanism is that lactic acidosis resulting from anaerobic conditions increases glomerular permeability, which allows the passage of erythrocytes into the urine .
Another potential cause of nontraumatic exercise-induced hematuria is nutcracker syndrome, which refers to compression of the left renal vein between the aorta and proximal superior mesenteric artery. Nutcracker syndrome can cause both microscopic and gross hematuria, primarily in children and primarily in Asia but also in adults. The hematuria is usually asymptomatic but may be associated with left flank pain. (See "Etiology and evaluation of hematuria in adults" and "Evaluation of microscopic hematuria in children" and "Evaluation of gross hematuria in children".)
Limited data suggest an association between hematuria (with or without left flank pain) and exercise in selected adults with nutcracker syndrome [18-20]. The diagnosis is established by Doppler ultrasonographic assessment of left renal vein diameter and peak velocity or by magnetic resonance angiography or renal venography [18,20,21]. Possible therapies in adults are discussed separately. (See "Etiology and evaluation of hematuria in adults".)
EVALUATION — Regardless of the mechanism, exercise-induced hematuria appears to be a benign condition with no known long-term morbidity. However, exercise-induced hematuria should be considered a diagnosis of exclusion. In addition to the temporal relation of onset following exercise, the hematuria should remit spontaneously within several days to one week [5,6]. If so, further diagnostic testing is not necessary in most patients.
Evaluation for other causes of hematuria is warranted if the hematuria persists well beyond one week of no exercise and may be warranted even with transient hematuria in patients (particularly men) over age 50 years (especially if recurrent) and selected other patients at increased risk for bladder or kidney cancer . (See "Etiology and evaluation of hematuria in adults" and "Epidemiology and risk factors of urothelial (transitional cell) carcinoma of the bladder", section on 'Risk factors' and "Epidemiology, pathology, and pathogenesis of renal cell carcinoma", section on 'Established risk factors'.)
It has been suggested that evaluation for underlying disease is warranted if the hematuria following exercise is not dysmorphic (ie, nonglomerular) . However, this recommendation only applies when the examiner has experience in identifying dysmorphic red cells and preferably has access to phase contrast microscopy.
Exercise-induced gross hematuria should be differentiated from two other potential causes of red to brown urine following exercise: myoglobinuria due to rhabdomyolysis; and march hemoglobinuria, probably resulting from trauma to red cells as they move through the blood vessels on the plantar aspects of the feet [5,23]. Exercise-induced hemolysis may also be seen in patients with alterations in erythrocyte membrane spectrins; it primarily occurs in the early phase of an ultraendurance race due to a relative older cell population . (See "Rhabdomyolysis: Epidemiology and etiology", section on 'Nontraumatic exertional' and "Non-immune (Coombs-negative) hemolytic anemias in adults", section on 'Foot strike or hand strike'.)
With myoglobinuria or hemoglobinuria, the urine dipstick is positive for heme in the urine supernatant, but hematuria is not seen on microscopic examination of the urine unless there is concurrent hematuria. The approach to patients with red to brown urine is discussed in detail separately. (See "Urinalysis in the diagnosis of kidney disease", section on 'Red to brown urine'.)
SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Glomerular disease in adults".)
INFORMATION FOR PATIENTS — UpToDate offers two types of patient education materials, "The Basics" and "Beyond the Basics." The Basics patient education pieces are written in plain language, at the 5th to 6th grade reading level, and they answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials. Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are written at the 10th to 12th grade reading level and are best for patients who want in-depth information and are comfortable with some medical jargon.
Here are the patient education articles that are relevant to this topic. We encourage you to print or e-mail these topics to your patients. (You can also locate patient education articles on a variety of subjects by searching on "patient info" and the keyword(s) of interest.)
●Beyond the Basics topics (see "Patient education: Blood in the urine (hematuria) in adults (Beyond the Basics)" and "Patient education: Glomerular disease (Beyond the Basics)")
SUMMARY AND RECOMMENDATIONS
●Overview – Exercise-induced hematuria can be defined as gross or microscopic hematuria (increased red cell excretion in the urine) that occurs after strenuous exercise and resolves with rest in individuals with no apparent underlying kidney or urinary tract pathology. It is a benign condition with no known long-term morbidity. (See 'Introduction' above and 'Evaluation' above.)
●Etiology and pathogenesis – Direct trauma to the kidneys and/or bladder may be responsible for hematuria associated with contact sports such as football and boxing. Trauma to the bladder may also occur with long-distance running and cycling. Hematuria that occurs in association with noncontact sports may be explained by nontraumatic mechanisms including kidney ischemia due to shunting of blood to exercising muscles and the nutcracker syndrome. (See 'Traumatic' above and 'Nontraumatic' above.)
●Evaluation – Exercise-induced hematuria should be considered a diagnosis of exclusion. In addition to the temporal relation of onset following exercise, the hematuria should remit spontaneously within several days to one week. If so, further diagnostic testing is not necessary in most patients. Evaluation for other causes is warranted if the hematuria persists beyond one week of no exercise and may be warranted even with transient hematuria in patients (particularly males) over age 50 years and selected other patients at increased risk for bladder or kidney cancer. (See 'Evaluation' above.)
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