a little step towards cost effectiveness - renal US

A renal ultrasound is a very good study that gives a lot of useful information for a lot of kidney diseases. Especially...in Acute Kidney injury(AKI) , it may change the management. But ,how frequently does it change the management...and how frequently should we do it in the setting of AKI? Well.......it gets done routinely in hospitals for evaluation of AKI ..to "rule out" obstruction. 
Recently...nephrologists at Yale tried to stratify patients who might need a renal US for evaluation of cause of hospital acquired AKI. (Arch of Int Med Nov 2010)


To identify the clinical risk factors for hydronephrosis, a derivation sample of 100 patients with hydronephrosis diagnosed with ultrasonography and 100 randomly selected controls was used. The results were subsequently validated using 797 ultrasonography studies obtained over 16 months. authors were able to find 7 factors associated with risk of hydronephrosis : history of hydronephrosis; recurrent urinary tract infections; diagnosis consistent with obstruction; nonblack race; and absence of the following: exposure to nephrotoxic medications, congestive heart failure, or prerenal AKI. 1 point awarded to each risk factor (except previous h/o hydro...which was considered high risk by itself). Pts were categorised into low risk(<2 points), intermediate risk(3 points) and high risk(>3 points). The overall incidence of hydro was 10%, and hydro needing intervention was 3%. In the low risk group...223 patients had to be screened to find one case of hydro needing intervention.(thats a lot of patients!). The model had very good sensitivity & a negative predictive value of 99% for hydro needing intervention. 


So......what do we have here?? A good proportion of patients with hospital AKI( categorised as low risk by this model) who would not need a renal US as part of their work up for AKI. The authors also calculated a savings of around $42,000 (based on a 30% reduction in US requests...($200/US) with an average of 700 US procedures in 1 year)


With regards to Community acquired AKI, we dont have similar kind of data...and the one we have is from 1991(AJKD) where they found the incidence of obstruction as a cause of AKI in 17% of patients with AKI...and it was mostly due to prostatic hypertrophy. It may be reasonable to do routine US in community acquired AKI until we have any new studies......as the mortality in the above study was 24% for those with obstruction.