Less is More

Despite the fact that the kidney ultrasound is generally obtained as one of multiple recommendations when evaluating AKI, the benefit of kidney ultrasound is not clear. The post-renal causes of AKI are not very common. It adds to the cost and can subject patients to unnecessary work-ups by revealing incidentalomas. How often, then, is the ultrasound useful? 

In order to assess the prevalence of the post-renal AKI and determine a cost-effective use of the ultrasound, a single-center case-control study was conducted.

Their conclusion is that the prevalence of hydronephrosis requiring stenting or nephrostomy placement was only 0.4% in the low-risk group. The number to screen to find a case of urinary obstruction was 223. At what cost? In our institution the kidney ultrasound without Doppler costs $600. It costs $133,800 to find one case.

Who is the low-risk group patient? Based on the multivariate analysis, a patient was considered low-risk if he or she did not have a history of hydronephrosis and had no more than one of the following:

1. Recurrent UTI

2. Diagnosis to suspected obstruction (BPH, abdominal or pelvic cancer, one functional kidney, neurogenic bladder, pelvic surgery)

3. Non-African American

4. Absence of:  exposure to the following medications (ASA, diuretics, ACEI or IV vancomycin), congestive heart failure, or pre-renal AKI.

The study has limitations. Not all AKI patients were studied. The cases requiring non-surgical interventions were not counted. If we would have to implement this strategy, we don’t know what the cost of missing some cases of obstruction would be.

However, the implication is that we should not routinely order kidney ultrasound on every patient with AKI, particularly those in the low-risk group. In this era of cost constraint on medicine, less is usually more…

Or, here is what you can do. If your place has an ultrasound on the floor, with a little training you can have a quick look at the kidneys just to rule out obstruction in low risk patients. You acquire one more diagnostic skill, your students have one more fun on round, and your hospital saves significant amount of money!

Posted by Tomoki Tsukahara