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.