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Abdominal Conditions: Section Articles

Renal Trauma

Evaluation, Management, and Return to Play

Bernard, Joseph J.

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Current Sports Medicine Reports: March 2009 - Volume 8 - Issue 2 - p 98-103
doi: 10.1249/JSR.0b013e31819e2e52
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The sports medicine physician will encounter a variety of renal injuries, both traumatic and atraumatic. Evaluation of these injuries requires knowledge of the sport-specific conditions in which the individual athlete participates and the mechanism of the injury that occurred. Management and return-to-play decisions will be based upon the physician's diagnosis and whether the condition requires more extensive evaluation before arriving at an accurate diagnosis.


Physiologic changes in renal function occur during exercise that can produce proteinuria, hematuria, and reduction in renal blood flow and glomerular filtration rate. In a normal state, the upper limit of urinary protein excretion is 80 mg·L−1 per 24 h. If proteinuria exceeds 100mg·L−1 in adults and 140 mg·(m2)−1 of body surface area in children, it usually is considered to be pathologic (8).

Transient proteinuria can be seen following physical activity (25). The reported prevalence of proteinuria during exercise ranges from 18% to 100% depending upon the type of exercise and its intensity (8). This has been seen in soldiers after long marches, as well as marathon runners (40). An increased incidence of proteinuria has been seen in athletes participating in sports requiring higher exercise intensity (40,41), such as boxing, wrestling, gymnastics, football, and rowing. Robertshaw et al. also stated that exercise-induced proteinuria was more related to the intensity of exercise than the duration of exercise, but was not seen in all the subjects after participation in strenuous exercise (43).

Exercise-induced proteinuria occurs as a result of increased glomerular permeability and partial inhibition of protein tubular reabsorption. During mild to moderate exercise, glomerular proteinuria usually is observed, while strenuous activity can produce a mix of both glomerular and tubular proteinuria (8).

It has been observed that the maximal protein excretion in the urine occurs about 20-30 min after a strenuous exercise session, and can take more than 4 h of rest for it to return to normal (41). Edes et al. found that in triathletes, there was a spontaneous decrease in exercise-induced proteinuria immediately after the race compared with mid-distance levels (20). If proteinuria does not disappear within24-48 h, further evaluation as to the cause of the proteinuria should be considered. It is unlikely that proteinuria associated with exercise will later result in chronic renal disease; therefore, there is no need to restrict physical activity.


Hematuria, or blood in the urine, can be a presenting finding in many different medical conditions. It also can present in exercise or sports participation. It can be both traumatic, as seen in contact sports like football and boxing, or it can be atraumatic, as seen in non-contact sports like running, rowing, and swimming. When seen in exercise without any known trauma, it is termed exercise-induced hematuria. Some other names used in the literature include sports hematuria, athletic pseudonephritis (22), and stress hematuria (10). It was first described in the medical literature nearly a century ago by Barach (7), who reported on long distance runners who developed hematuria after completing a 40-km race. The condition was reported in 1700, and may have been recognized as early as the first century A.D. (11).

Microscopic hematuria can be seen frequently in asymptomatic individuals in both the athletic and the non-athletic population. The prevalence of asymptomatic microscopic hematuria in the general population varies from 0.19% to as high as 21%, depending upon the age and sex of the population or the amount of screenings (24). The American Urologic Association defines microscopic hematuria as three or more red blood cells per high-power field on microscopic evaluation of urinary sediment from two of three properly collected urinalysis specimens (24).

There have been many attempts at trying to determine the incidence of microscopic hematuria in the general population. One study examined the urine of 1000 medical students and found an incidence of 13% (31). Another study reviewed the medical records of 100 asymptomatic servicemen over a 15-yr period and found the incidence of microscopic hematuria in this group to be 38% (21). In a population-based study at the Mayo Clinic, asymptomatic hematuria was found in 13% of adult males over 35 yr of age and postmenopausal women over 55 yr of age (35).

In the athletic population, the reported incidence is usually higher. In one study, Alyea and Parish (3) investigated athletes of various sports and found that swimmers, track, and lacrosse athletes had an incidence of hematuria following participation in their sport of about 80%. Football players and rowers had an incidence of hematuria of about 55%. In a study of 50 marathon runners, Siegel et al. (47) found that 18% developed hematuria during the race. Of these cases, all had completely resolved by 48 h after the race. In exercise-induced hematuria, resolution usually occurs spontaneously after the physical activity ends, whereas in the non-athlete with microscopic hematuria, the condition may be chronic.


The etiology of exercise-induced hematuria is not well understood. Many proposed mechanisms exist, including bladder or kidney trauma, hemolysis, dehydration, peroxidation of red blood cells, and renal ischemia (28). With traumatic hematuria, there is a greater incidence of gross hematuria. This usually is seen with a direct blow or penetrating injury. The pathophysiology and etiology of sports-induced hematuria, or atraumatic hematuria, can be divided into mechanisms related to exercise duration or exercise intensity. Traumatic hematuria will be discussed further in the renal trauma section.

Exercise Duration

"Foot-strike hemolysis" can be seen in long-distance runners where trauma occurs to the red blood cells circulating through the runner's foot. With slight hemolysis, no hemoglobin is lost in the urine. When the hemolysis is significant, the haptoglobin-binding sites become overloaded and excess hemoglobin is lost in the urine (28). Evaluation of the urine in this case will not show the presence of red blood cells, but only the hemoglobin. This is seen in higher incidence in sports involving more foot trauma and in lower incidence in sports like swimming.

Hematuria also can be the result of bladder trauma, such as Blacklock described when he saw cytoscopic alterations of eight marathon runners with no identifiable upper tract lesion (9). It is thought that the repeated impact of the flaccid posterior vesical wall against its base may be the underlying cause of these lesions and subsequent hematuria (8). Maintaining a small amount of urine in the bladder to help cushion the repeated trauma may be helpful in preventing bladder trauma and subsequent hematuria (9). There was also a case report by Lüthje and Nurmi of a runner that developed recurring exercise-related macroscopic hematuria believed to be caused by the blood vessels in the posterior wall of the bladder (30). In this case, cystoscopy revealed crossing but otherwise normal appearing vessels in the posterior wall of the bladder. The hematuria did not resolve until these vessels were electrocoagulated.

Other proposed mechanisms of hematuria related to exercise duration are hemolysis secondary to dehydration, destruction of erythrocytes from increased body temperature, hemolysis from increased production of free radicals, liberation of hemolyzing factors, and excessive release of catecholamines (8).

Exercise Intensity

While exercising, blood is shunted away from the kidneys to supply the muscles. Epinephrine and norepinephrine are released, causing renal vasoconstriction. During intense exercise, renal blood flow may decrease from 1000 mL·min−1 at rest to 200 mL·min−1 with exercise. With a decrease in the glomerular filtration rate, there is an increase in renal filtration and an increase in glomerular permeability, allowing red blood cells to pass into the urine (39). It also has been described that with strenuous exercise, there is a decrease in the blood supply to the spiral arteriole vessels, resulting in ischemia (6). The vessels become fragile, and with the return of normal blood supply, the vessels may shed red blood cells into the urine. With intense exercise activity, there are increased concentrations of lactic acid, which by increasing glomerular concentration can induce the passage of erythrocytes into the urine (8). Muscle membranes are ruptured with physical activity, increasing serum myoglobin concentration, which, due to its low molecular weight, can be filtered easily through the glomeruli and into the urine (19). This usually occurs within 24-48 h after exercise.

Other Causes

Transient microscopic hematuria can be seen in other conditions as well. Trauma to the urethra or prostate in cyclists has been reported to be a cause of hematuria, specifically in children riding banana-style seats (29). Routine work up of a urinary tract infection is a common reason to have found microscopic hematuria, and this should resolve after adequate treatment of the infection. It also can be seen after sexual intercourse, digital rectal prostate exam, or menstrual contamination. In addition, one must consider causes of renal injury and subsequent hematuria such as medications, intrinsic renal disease, renal stones, and neoplasm. The urine also can become discolored from certain foods, which may have an appearance similar to blood in the urine.


Evaluation in the athlete should begin with a thorough medical history and physical examination. Keys in the history should include the relation of the hematuria to exercise, the duration of the symptoms, the type and intensity of the exercise, and other potential risk factors. The presence of pain may be caused by kidney stones or an infection. The presence of painless, gross hematuria in an adult should be considered bladder cancer until proven otherwise.

Initial laboratory evaluation should include a urine dipstick test and microscopic examination of the urine. A urine dipstick test may be positive for blood caused by hematuria, hemoglobinuria, or myoglobinuria. Microscopic examination can help differentiate from other causes of discolored urine, such as hemoglobinuria, myoglobinuria, hematospermia, or ingested substances by looking for the presence of red blood cells (33). The appearance of red blood cells can help determine the origin of the hematuria. Dysmorphic red blood cells are seen if the hematuria is from a glomerular source such as a glomerulonephritis. Isomorphic red blood cells are seen if the hematuria is post-renal (9). A diagnosis of exercise-induced hematuria can usually be made in an athlete under the age of 40 yr whose hematuria occurs in the absence of other signs or symptoms, was seen following exercise, and that clears with rest (16). If exercise-induced hematuria is the suspected cause, the urinalysis should be repeated in 24-72 h to assess for resolution of the hematuria.


A reasonable approach to management suggested includes 1) evaluation of the urinalysis for abnormalities, 2) reevaluation of the athlete and urinalysis after 48-72 h of rest, 3) investigation of secondary causes such as a history of trauma, pain, urgency, dysuria, passage of clots, or recent infections, 4) determination of any history of prior renal disease, 5) obtaining a serum blood urea nitrogen, creatinine, and complete blood count, and 6) further evaluation of those athletes with persistent urinary abnormalities or a suspicious history (8).

Return to Play

In asymptomatic microscopic hematuria that resolves and is determined to be related to exercise, there is little evidence that there is any need to restrict exercise or sports participation. An athlete who is determined to have underlying renal disease with impaired renal function should not necessarily be withheld from exercise, but should be counseled on the possible harmful effects of strenuous exercise upon kidney function and should undergo close monitoring of the renal function (1,16).


Renal injury needs to be considered when evaluating an athlete with blunt trauma to the abdomen or flank. Penetrating injuries also can occur in sports involving high velocity objects, such as a javelin in track and field events, or a high velocity impact, such as seen in skiing accidents.

In adult renal trauma, two important indicators in determining the severity of the injury are hematuria and hypotension. Other indicators include the presence of flank hematoma, abdominal or flank tenderness, rib fractures, and penetrating injuries to the low thorax or flank (2). In a study of 2254 adult patients with blunt renal trauma, no significant renal injuries were missed without gross hematuria, hypotension, or significant mechanism of injury (rapid deceleration or high falls) (34). Those with gross hematuria or microscopic hematuria and shock have a higher incidence of significant renal injury; therefore, imaging is necessary in those instances.

Children are more likely than adults to sustain renal injury from blunt abdominal trauma. Proposed reasons for this include the relative greater size of the kidney in relation to the body, decreased perirenal fat, weaker abdominal muscles, and less protection from the rib cage (13). Blunt trauma accounts for approximately 90% of pediatric renal injuries, with the remainder caused by penetrating injury (15). The decision on who needs further work-up and who can be monitored becomes a challenge. In children, hypotension is not an accurate indicator of hypovolemia as it is in adults. Therefore, it is important to perform serial clinical examinations, blood pressure readings, and hematocrit levels in all children that sustain a significant renal trauma (15). Perez-Brayfield et al. retrospectively reviewed the records of 110 children with blunt trauma and hematuria. They found that significant renal injuries were not missed if radiographic evaluation with a CT scan of the abdomen and pelvis were performed on patients with 50 or greater red blood cells on urinalysis, hypotension, or based upon mechanism of the injury, such as high speed deceleration injuries (38). Buckley et al. retrospectively reviewed 374 pediatric renal trauma patients and concluded that the children with abdominal, flank, or pelvic pain, or ecchymosis, those who have significant microscopic hematuria (greater than 50), or those who were involved in a rapid deceleration injury should undergo further imaging with a CT scan (14).


Initial evaluation of an athlete with an abdominal or flank trauma should include a thorough history and physical examination. Keys to the history include the sport that the athlete was participating in at the time of the injury, the nature of the injury, and the symptoms that are present, including gross hematuria. Additional evaluation with a urinalysis, complete blood count, electrolytes, liver function tests, creatinine, glucose, amylase, lipase, and HCG should be performed. Initial imaging may include plain radiographs followed by a CT scan or IV urography (50).

The gold standard for imaging renal injuries is contrast-enhanced CT (26). Findings on CT scan that suggest a major injury include medial hematoma, medial extravasation on delayed films, and any lack of parenchymal contrast on the early phase (2).

When evaluating renal injuries with a CT scan, most institutions will use a three-phase protocol, as it allows for the most thorough evaluation of the urinary tract (37). This consists of an initial unenhanced phase, a second phase following the administration of nonionic contrast material acquired following a delay of 90-100 sec (nephrographic phase), and then the pyelographic phase, taken 5-15 min following contrast administration. The nephrographic phase is used to evaluate the renal parenchyma for masses, and the pyelographic phase evaluates the urothelium from the pelvicaliceal system to the bladder (37).


The Organ Injury Severity Scale for the kidney, as well as other organs, was developed by the American Association for the Surgery of Trauma (AAST) (36). It is used to help grade kidney injuries and classify the need for surgery. The scale classifies injuries as contusion (grade I), hematoma (grade I or II), laceration without extravasation (grade II or III), laceration with extravasation, or vascular injury without avulsion of the hilum (grade IV), and shattered or fractured kidney or vascular injury with hilar avulsion (grade V) (36). The scale was validated by a retrospective review of 2467 patients done by Santucci et al., confirming the scale as a good predictor of need for surgical repair (45). It has been determined that all minor (Grades I-II) and many major (Grades III-IV) renal injuries can be managed with expectant management (44). Adults with microscopic hematuria, but in the absence of hypotension or a deceleration injury, can be managed conservatively without the need for imaging (44). In pediatric patients, there should be a much lower threshold for imaging studies. Three reasons that a pediatric renal trauma patient would need immediate exploration include hemodynamic instability, a penetrating injury, or associated non-renal injuries that would require operative exploration (15). Most blunt pediatric renal injuries are managed successfully without operative intervention with CT grading and staging (14).

Return to Play

The majority of sports-related renal injuries involve contusions (grade I) that can be managed conservatively with observation and supportive care (16). In addition, some other grade I and II injuries, as well as some grade III injuries, can be managed with observation (44).

Athletes should not return to sports participation until the hematuria has completely resolved. The reported time away from sports varies from 2 to 6 wk in the literature (16). In a study of professional football players that sustained renal injuries, most were back to participation within 2 wk (12). It would be reasonable to keep a pediatric athlete out for longer to allow complete recovery, although no consensus statement exists on the appropriate time frame. More severe injuries, such as laceration with diastasis may take longer to heal. Return to contact sports may require 6-12 months in these more extensive renal injuries (16).


Special consideration needs to be given to an athlete with a solitary kidney. A physician may be asked to clear such an athlete for participation in sports, but automatic disqualification is not always necessary. This becomes a controversial issue, especially pertaining to contact sports. Often there is a conflict between what the physician feels is best for the health of the young athlete and the strong drive and desire for the athlete to participate in sports.

In 1988 the American Academy of Pediatrics (AAP) Committee on Sports Medicine and Fitness recommended that children with a solitary kidney not participate in contact sports (5). This was readdressed in 1994 and again in 2001 (17) where participation in sports for those with the absence of one kidney was granted a "qualified yes" with "individual assessment for contact, collision, and limited-contact sports."

In 2001, a survey was mailed to 231 active members of the AAP, Section of Urology, and included questions regarding counseling of patients with a solitary kidney and the physician estimates of renal loss due to various causes (46). Of the 182 respondents, 68% of the respondents recommended that patients with a solitary kidney avoid contact sports, yet 88% felt that the estimated risk of renal loss from participation in contact sports was less than 1%, adding to the disparity of opinions on this matter.

The current literature does not demonstrate that contact or team sports are a major cause of kidney loss from trauma (27). A recent retrospective review by Wu et al. of 115 blunt injuries showed that dirt bikes, all-terrain vehicles, and bicycles were more likely to cause renal trauma than contact sports (51). Another review of 68 renal injuries in children showed that most renal injuries were associated with bicycle accidents rather than contact sports (23). A review by McAleer et al. of 14,763 patients in a trauma registry found 193 renal injuries, of which 113 occurred during recreational or team sport activity. Of the 113 injuries, 10 occurred in a team sport, and no kidneys were lost in those that participated in team sports (32). These studies demonstrate that it may not be necessary to recommend against team sports participation in patients with a solitary kidney.

Johnson et al. analyzed data that was collected by the National Pediatric Trauma Registry (NTPR) from 1995-2001 on 49,651 pediatric trauma cases. Of these, 813 suffered renal injuries. A total of 28 kidneys were lost, of which a majority (21 of 28) occurred as a result of motor vehicle accidents, pedestrians being struck by a vehicle or other object, and falls. There were 85 individuals who suffered a sports-related renal injury with no kidneys lost in this group (27). In the renal injuries that were a result of sports participation, they found that most occurred with football, and that the overall severity of these injuries was low.

Wan et al. also analyzed results from the NTPR, collecting data on 81,923 trauma cases from 1990-1999, and 5439 of the injuries resulted from sports participation. The spleen was the most injured organ with 96 cases, followed by the kidney with only 42 cases. None of the injuries resulted in physical or functional loss of the kidney (49).

Radelet et al. performed an observational cohort study of 7- to 13-yr-old children participating in football, baseball, softball, and soccer, and found no documented renal injuries over a 2-yr period (42). Stuart et al. performed a prospective observational cohort analysis of 915 youth football players aged 9-13 yr and found no renal injuries (48). In an older study, DeLee et al. followed 4000 varsity high school football players for one season and found 97 injuries requiring hospitalization or surgery, but no renal injuries (18).

Sports that are listed as "limited contact sports," such as skiing, snowboarding, and in-line skating account for more renal loss than do some of the contact sports (27). Motor vehicle accidents, pedestrians being struck, and falls were all associated with higher rates of kidney loss than any of the sports were.

A recent case series by Brophy et al. looked at kidney injuries in the National Football League (NFL) and found renal trauma to be rare, and most athletes recovered to play without any re-injury reported to the previously injured kidney. Of the 52 renal injuries found, 18 hospitalization required, but none required surgery (12).

The Preparticipation Physical Evaluation monograph, written by members of many of the major primary care and sports medicine organizations, developed a consensus opinion stating that "If the athlete chooses to play in a sport that may place a solitary kidney at increased risk for damage, a full explanation should be given to the athlete, his or her parent(s) or guardian(s) and the coaches. The explanation should include available protection (e.g., flak jacket), potential serious long-term consequences, and treatment of injuries if they occur" (4).

Most of the literature shows a very small risk of kidney injury, even with contact sports. In the few injuries that do occur, rarely is there kidney damage that does not completely recover without permanent and irreversible damage. The athlete with a solitary kidney that is participating in limited and noncontact sports should not be withheld from participation, but it is important to discuss with them the risk of renal injury even in sports that are considered limited contact, and in recreational activities such as riding a bike. Protective equipment such as flak jackets can be worn in an attempt to make participation in contact sports safer.


The sports medicine physician should be aware of the traumatic and atraumatic injuries that can occur to the kidney with athletic participation and exercise. Physiologic changes in renal function can occur during exercise that can lead to proteinuria and hematuria without any other injury or trauma. In the majority of cases, proteinuria and hematuria are benign and resolve spontaneously. They can be monitored without the need for any further work-up or imaging unless proteinuria or hematuria persists. With abdominal trauma, a decision on further work-up, including imaging, depends upon whether the athlete is an adult or child, the type of injury, presence of hypotension, or the length of the symptoms, including microscopic hematuria. The athlete with a solitary kidney brings an interesting challenge, but with the available information in the literature, it appears that sports participation is generally safe, with very minimal risk to the remaining kidney.


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