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Three Part Question

In [adults (18+) presenting to the A&E with acute renal failure] does [ultrasonography] effectively [rule out obstructive uropathy]

Clinical Scenario

A patient presents to your A&E with signs of obstructive uropathy. You are reaching for the ultrasound machine, but then wonder if this accepted method of diagnosis is actually backed up by evidence. Perhaps another form of imaging would be better? You take it upon yourself to answer this question.

Search Strategy

Medline 1950- July 2007, Embase 1980 – July 2007, ACP Journal Club 1991 to May/June 2007, Cochrane Central Register of Controlled Trials 3rd Quarter 2007, Cochrane Database of Systematic Reviews 2nd Quarter 2007, Database of Abstracts of Reviews of Effects 2nd Quarter 2007 using the OVID interface.
([ultrasound.mp or exp Ultrasonography/] AND [calculus.mp OR exp Kidney Calculi/ OR exp Ureteral Calculi OR exp Ureteral Obstruction/ OR obstructive uropathy.mp] AND [hydronephrosis.mp OR exp Hydronephrosis] limit to humans and English language)

Search Outcome

610 papers were found of which 11 were relevant, although one was discarded due to poor quality.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Watkins, S. et al 2007 Australia	57 patients underwent emergency ultrasound by a physician, results were compared to a CT done by a senior radiologist.	Comparative study.	Sensitivity of ultrasound	80% (95% CI 65-89%)	small patient group
			Specificity of ultrasound	83% (95% CI 61-94%)
			Positive predictive value of ultrasound	91% (95% CI 75-98%)
			Negative predictive value of ultrasound	65% (95% CI 43-83%)
			Overall accuracy of ultrasound	81% (95% CI 69-89%)
Gaspari, R.J. et al 2005 USA	58 patients underwent emergency ultrasound by a physician, results were compared to CT scan results.	Comparative study	Ultrasound detection of hydronephrosis	Sensitiviy: 86.8 (95% CI = 78.8 to 92.3), specificity: 82.4 (95% CI = 74.1 to 88.1)	small patient group
			Ultrasound detection of hydronephrosis in patients with hematuria	Sensitivity: 87.8 (95% CI = 80.3 to 92.5), specificity: 84.8 (95% CI = 73.7 to 91.9)
Ather, M.H. et al 2004 Pakistan	34 patients underwent ultrasound kidney, and results compared to un-enhanced helical CT.	Comparative study	Ultrasound detection of renal stones:	Sensitivity 81%, specificity 100%	Small patient group
			Ultrasound detection of hydronephrosis:	Sensitivity 93%, specificity 100%
			Ultrasound detection of ureteric stone:	Sensitivity 46%
			Ultrasound detection of hydroureter:	Sensitivity 50%
			X-ray KUB + ultrasound for ureteric stones:	Sensitivity 77%
Catalano, O. et al. 2002 Italy	277 patients with acute flank pain underwent unenhanced radiography, sonography, and unenhanced helical CT or primary unenhanced helical CT or unenhanced radiography and sonography with the addition of helical CT in unclear cases. Results shown are for Ultrasound with KUB X-ray.	Comparative study	Sensitivity:	77.1%	Changing of CT method due to update of machinery
			Specificity:	92.7%
			Positive predictive value:	95.3%
			Negative predictive value:	68%
			Overall diagnostic accuracy	82.5%
Patlas, M. et al 2001 England	62 consecutive patients with flank pain were examined with both CT and US over a period of 9 months	Comparative study	Sensitivity of US for detection of renal stones:	93%	Small patient group
			Specificity of US for detection of renal stones:	95%
Haddad, M.C. et al 1992 Saudi Arabia	101 consecutive patients with renal colic were evaluated with US by two technicians, followed immediately by IVU	Comparative study	US diagnosis of acute urinary tract obstruction:	Sensitivities of 2 technicians: 91% and 92%; specificity 90%	Small patient group, no gold standard comparison test.
			US with KUB radiography:	Sensitivities of 2 technicians: 94% and 97%; specificity 90%
Aslaksen, A. et al 1990 Norway	46 patients with ureteral calculi, of which 35 had and 11 did not have hydronephrosis, all underwent ultrasound.	Comparative study	Ureteral calculi diagnosed by US:	Sensitivity 37%	poor study design, small patient group, no gold standard comparison
			Hydronephrosis found, and taken to mean calculi:	Sensitivity 74%
Mitterberger, M. et al 2007 Germany	62 patients in the urologic clinic with clinical suspicion of distal ureteral calculi, all underwent 3D transrectal/transvaginal sonography and transabdominal sonography with IVU.	Comparative study	US diagnosis of calculi:	Sensitivity 55%	Small patient group.
			IVU alone:	Sensitivity 71%
			Combination transabdominal sonography and IVU:	Sensitivity 81%
			Three-dimensional transrectal/transvaginal sonography:	Sensitivity and specificity 100%
Kundu, A.K. et al 1996 India	58 patients with acute recurrent or persistent flank pain, all underwent plain KUB x-ray and ultrasound.	Comparative study	KUB X-ray identification of calculi:	Sensitivity 86.2%	Small patient group, no gold standard comparison
			US identification of calculi:	Sensitivity 94.8%
Sinclair, D. et al 1989 Canada	98 patients with acute flank, abdominal pain or both, all underwent standardized ultrasound scan and excretory urography. Staff radiologists were blinded to the results of the other test and clinical outcome. Urinary calculus diagnosed by identification of calculus at surgery or by passage of a stone. 85 patients followed-up, calculi were identified in 69 (81%).	Comparative study	Calculi identified by ultrasound:	44 patients (sensitivity 64%; specificity 100%)	Small patient group
			Calculi identified by excretory urography:	44 patients (identical sensitivity and specificity)

Comment(s)

Ultrasound has had a role in the diagnosis of kidney pathologies for some time, but there has been surprisingly little work done looking at how effective it actually is. These studies have highlighted a number of the shortcomings of ultrasound. In particular, the variability of results between different papers is in keeping with the notorious user-dependability of ultrasound. This is particularly well shown by Haddad et al, who found differences between two operators on the same patients. The general findings of these papers are that ultrasound is able to detect calculi and hydronephrosis in a high percent of patients. It's positive predictive value is excellent, and if hydronephrosis or calculi are identified by ultrasound, a confident diagnosis can be made. However, the negative predictive power of ultrasound is not as strong. In the absence of hydronephrosis or a calculus, these conditions cannot be definitively ruled out, as ~1 in 5 patients will still have an obstruction. In patients with strong clinical evidence of obstruction, but a negative ultrasound report, either another form of imaging should be considered, or ultrasound should be repeated at regular intervals to look for developing hydronephrosis. A number of these studies also highlight that the diagnostic ability of ultrasound is increased when used in conjunction with another form of imaging. For most clinicians the most convenient will probably be KUB X-ray.

Clinical Bottom Line

Ultrasound should be used in conjunction with another form of imaging to try and identify obstructive uropathy in all patients where it is suspected. However in the case of a negative ultrasound result, obstructive pathologies should still remain a possible diagnosis and further tests should be undertaken to try and confirm a diagnosis.

References

1. Watkins, S. et al Validation of emergency physician ultrasound in diagnosing hydronephrosis in ureteric colic Emerg Med Australas 19(3); 188-95
2. Gaspari, R.J. et al Emergency ultrasound and urinalysis in the evaluation of flank pain Acad Emerg Med 12(12); 1180-4
3. Ather, M.H. et al Diagnostic accuracy of ultrasonography compared to unenhanced CT for stone and obstruction in patients with renal failure BMC Med Imaging 4(1); 2
4. Catalano, O. et al. Suspected ureteral colic: primary helical CT versus selective helical CT after unenhanced radiography and sonography Am J Roentgenol 178(2); 379-87
5. Patlas, M. et al Ultrasound vs CT for the detection of ureteric stones in patients with renal colic Br J Radiol 74(886); 901-4
6. Haddad, M.C. et al Renal colic: diagnosis and outcome Radiology 184(1); 83-8
7. Aslaksen, A. et al Ultrasonic diagnosis of ureteral calculi in patients with acute flank pain Eur J Radiol 11(2); 87-90
8. Mitterberger, M. et al Value of 3-dimensional transrectal/transvaginal sonography in diagnosis of distal ureteral calculi J Ultrasound Med 26(1); 19-27
9. Kundu, A.K. et al Ultrasonography in acute flank pain J Indian Med Assoc 94(11); 403-4, 416
10. Sinclair, D. et al The evaluation of suspected renal colic: Ultrasound scan versus excretory urography Ann Emerg Med 18(5); 556-9