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Blunt Kidney Trauma and Microscopic haematuria


Bottom line

Gross haematuria must be taken seriously as it raises the likelihood of finding significant renal pathology

Microhaematuria of any degree is most useful when serial urinalyses are performed.  Seeing a downward trend in the degree of microhaematuria is much more useful than the actual number.

The received wisdom suggesting a microhaematuria of 50RBC/HPF is the dividing line between trivial and significant haematuria is not supported by much evidence.

Microhaematuria in a child with a possible renal injury is best managed by serial examination, serial FBC, and serial urinalysis.  Discharge is safe if the examination remains stable, the FBC is stable, and the microhaematuria resolves.

There is no role for the urine dipstick in suspected renal injury.

Adult imaging protocols may be applied to paediatric blunt trauma though with some important provisos

Should children with suspected renal injury have their urine dipped?

The urine dipstick has no role in the work-up of paediatric blunt trauma.  The false-negative rate approaches 20%.  A similarly poor false positive rate will also lead to over-investigation of trivial injury if given undue importance.

If you think renal injury is possible based on the mechanism of injury, then simply send the urine for urinalysis.  You shouldn’t be reassured by a negative dipstick, nor should you be concerned by a positive dipstick: the dipstick simply is not useful in this context.

How do I interpret no haematuria/microscopic haematuria?

No haematuria does not mean you can stop thinking about the possibility of renal injury.  In one series of 720 patients, 25% of major renal injuries and 5% of minor renal injuries presented with no haematuria on the initial urinalysis.  This series included penetrating trauma, but there were patients with significant renal injury secondary to blunt trauma who had negative urinalyses.  Depending upon your index of suspicion (based upon the mechanism of injury), you could repeat the physical examination and urine after a spell in SSU, or you could ask the GP to repeat the exam and the urinalysis in the community.

Microscopic haematuria does not usefully predict the presence or absence of significant renal injury.  If you have a patient for whom the mechanism of injury could possibly cause renal injury, and if they have microscopic haematuria, the best thing to do is simply repeat the test and observe the trend.  You should also repeat the physical examination and the full blood count.  If the exam and FBC are stable, and the microhaematuria resolves, you can discharge this patient without imaging.

Obviously, a patient with an obvious indication for imaging (shock, physical exam findings) shouldn’t be managed expectantly just because they have microscopic haematuria: no algorithm is the solution to every scenario.  These suggestions are for the patient who could feasibly have a renal injury, but who has no signs of it other than microscopic haematuria.

If you have a patient who you really don’t think could possibly have renal trauma based on the mechanism then you should rethink doing the urinalysis in the first place

Should the degree of microscopic haematuria affect my management?

There seems to be anecdotal wisdom in some emergency departments that you can safely exclude significant renal injury if the urinalysis demonstrates <50RBC/HPF.  This comes from a study by Morey et al – a series of 180 children who suffered blunt trauma and had microhaematuria were looked at retrospectively.  It was noted that none of the 103 patients with <50RBC/HPF had a significant renal injury, but one patient with 50RBC/HPF had a Grade 5 renal injury. They concluded that therefore 50RBC/HPF is an important threshold.

Putting aside the small sample size and the lack of anatomical uniformity across different paediatric age groups, there are newer studies which include cases of significant trauma with a negative urinalysis.  For this reason, you should not be reassured by a microhaematuria <50, though nor should you rush into imaging for a microhaematuria of >50 in the absence of other indications.

So what do I do with a blunt trauma patient who has a normal exam and normal FBC AND has microhaematuria?

Serial examination, serial FBC, and serial urinalysis.  A four-hour interval is reasonable if the child seems otherwise fine.  If the examination and the FBC are stable and the microhaematuria resolves, you can discharge this child.

Can I use adult protocols for suspected renal injury in children with blunt-force trauma?

There are two large papers (large in the context of a small body of research) which consider this question. One was a retrospective study which considers 720 patients with suspected renal trauma,  and the other was a prospective study looking at 39 children with suspected renal trauma at a Level 1 Paediatric Trauma centre in the USA.  Both found that it is acceptable to use adult imaging protocols in paediatric patients.  I would add the following caveats:

(A) All of these studies are from Level 1 trauma centres which would surely have a higher prevalence of actual renal injury in their population of ‘suspicious for renal injury.’  The only prospective study is also a small study of only 39 patients.

(B) Similarly, the clinical acumen needed to decide whether to sieve a patient through the suspected renal injury pathway as opposed to not being concerned will be, on average, better in a Level 1 trauma centre than at the average community emergency department.

(C) Both studies are American. The pressure on beds is not as bad, I suspect, in the hospitals which have done these studies as it would be in Australia.   Serial examination with longer stays is more practical in such a setting.

(D) We (Australians) are rightly or wrongly much more cautious with paediatric CT than the Americans.  If we use the same decision-making process for imaging versus no-imaging as the USA, but then do an ultrasound instead of a CT, this may make the adult suspected renal injury protocol less able to exclude paediatric renal injury.

(E) Lastly, and it is worth re-iterating, the pre-test probability for renal injury for any given traumatic force will be higher for the younger end of paediatrics than the older end.  However, all of these studies lump 0-16 as ‘paediatric’.  I doubt even a large study like Study 8 is powered to make any recommendation about specific, anatomically similar age brackets (like ages 0-2 etc) – and so the application of any of this to a very young population is probably completely unjustified.

I’m not so sold on what seems to be the dogma that ‘some evidence is better than no evidence. Misapplied evidence is probably much worse than no evidence and would be better replaced by cautious and sober judgement.

Selected References

Fitzgerald, C. et al (2011) ‘Instituting a Conservative Management Protocol for Pediatric Blunt Renal Trauma: Evaluation of a Prospectively Maintained Patient Registry’, The Journal of Urology, vol. 185 pp. 1058-1064.

Perez-Brayfield, M. et al (2002) ‘Blunt Traumatic Hematuria in Children. Is a Simplified Algorithm Justified?’ The Journal of Urology, vol. 167 pp. 2543-2547.

Mandour, A. et al (1981) ‘Blunt Renal Trauma in the Pediatric Patient’, Journal of Pediatric Surgery, vol. 16 pp. 669-775.

Nguyen, M, and Das, S (2002) ‘Pediatric Renal Trauma’, Pediatric Urology, vol. 59 pp. 762-767.

Goldner, A. et al (1985) ‘Are Urine Dipsticks Reliable Indicators of Hematuria in Blunt Trauma Patients?’, Annals of Emergency Medicine, vol. 14 pp 580-582.

Thorp, A. et al (2011) ‘Test Characteristics of Urinalysis to Predict Urologic Injury in Children’, Western Journal of Emergency Medicine, vol. 12 pp. 168-172.

Morey, A. et al (1996) ‘Efficacy of Radiographic Imaging in Pediatric Blunt Renal Trauma’, The Journal of Urology’, 156 pp. 2014-2018.

Santucci, R. et al (2004) ‘Traumatic Hematuria in Children can be Evaluated as in Adults’, The Journal of Urology, vol. 171 pp. 822-825.



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3 thoughts on “Blunt Kidney Trauma and Microscopic haematuria”

  1. Hey Taylan and Tim. Thanks both for this thorough piece and the valuable context added by your comment Tim. I don’t use urine dipsticks routinely as part of my work up of BAT for reasons you have very much covered between you. Tim I agree it is all about mechanism, which in trauma provides the pre-test probability. As we have discussed a few times on DFTB positive/negative predictive values are dependent on the pre-test probability (and it is the PPV/NPV I really care about when making decisions about an individual patient). Bottom line for me – if I am worried based on the mechanism a negative urinalysis is not gonna stop me worrying, If I am not worried based on mechanism/exam a positive dipstick in macroscopically normal urine is not gonna persuade me to irradiate a kids abdomen on its own. As always, great to hear other’s perspectives. Thanks again for the effort that has gone into this piece and the insight thats gone into the comment.

  2. Greetings Dr Gurgenci —

    Thank you for a well balanced, researched, and thoughtful post!

    I appreciate your highlighting the possible use of microscopic hematuria in the use of blunt abdominal trauma (BAT). My thoughts are really in line with yours. Here I’ll just add a little of my personal thoughts. In my interpretation of the (scant) literature and personal experience, using microscopic hematuria in trauma falls in to a specific, but important scenario.

    First, adults with gross hematuria after BAT = CT imaging.

    In children, however, our threshold has to be lower, since their anatomy does not shield them from external forces, and significant injury can be present without major external signs of trauma. The cut off of 25-50 RBCs/hpf began as a consensus decades ago, but it has been useful in a dearth of clinical trial data. This may seem to go against the general trend of less diagnostic radiation in children — BAT is a special case.

    The main factor here is mechanism. If the mechanism of injury is significant (e.g. fall from building, auto v pedestrian, high-velocity blunt object, assault, etc) with symptoms and/or signs of trauma, CT imaging is typically considered. On the other hand, in a low energy mechanism (fall from standing, restrained passenger in low-speed MVC) with no real symptoms, normal exam, and likely normal other labs, a few RBCs would not typically trigger advanced imaging, perhaps only serial exams, admit for observation, etc.

    The scenario where microscopic hematuria may be directive is in the in-between cases, such as a low mechanism with discordant (more than expected) symptoms. These children appear well, and by mechanism you may not be so concerned, but the history or the physical does not totally match. In these stable, potentially seemingly well children, a urinalysis to screen for microscopic hematuria may help to risk-stratify and change your approach: rather than home, you may elect to observe or pull the trigger for imaging. For example, a well child with initial fright after a low-speed MVC gets a urinalysis as a low pre-test probability, no-to-low RBCs, continues to do well, likely will not need imaging, and likely will go home.

    Most significant pediatric BAT (severe mechanism and/or concerning clinical findings) is managed expectantly — even higher-grade splenic or liver lacerations — but the CT is essential to do this safely, so that the child’s need for intervention (OR or IR) is assessed and contingency plans made.

    In other words, it’s really all about the mechanism and your clinical assessment. In high-energy/severe mechanism, just get the imaging, you’ll be glad you did. Low energy, low mechanism, you can use any combination of signs, symptoms, labs, and urinalysis to help you decide home or observation, with or without imaging.

    Ok, just adding my take to your excellent treatment of the topic — thanks very much for doing this! Would love to hear your thoughts and others’ approaches!

    1. Thanks very much for the thoughtful comments, Tim. I agree with everything you have said above which can really be summarized by one key sentence you wrote – that “The scenario where microscopic haematuria may be directive is in the in-between cases…” The only thing I might highlight is the utility of the trend in the magnitude of haematuria as an additional parameter during your observation.

      I was also glad to see you reiterate the importance of keeping anatomical difference between age brackets at the front of our minds in these sort of cases.

      Thanks again.