Nancy A. Melville

November 18, 2013

ATLANTA — A low-tech dipstick for measuring saliva urea nitrogen levels has similar diagnostic accuracy to blood urea nitrogen levels, providing a potentially vital tool for identifying acute kidney injury in resource-strapped settings, according to findings presented here at Kidney Week 2013: the American Society of Nephrology 46th Annual Meeting.

"In regions of the developing world without organized medical facilities, this device could facilitate the handling of patients with suspected acute kidney failure," said lead investigator Viviane Calice da Silva, MD, a nephrologist with Pro-Rim Foundation, in Joinville, Brazil.

Dr. Calice da Silva and her team measured unstimulated salvia from 44 patients who were hospitalized with suspected kidney injury and compared the results with the patients' blood urea nitrogen.

Among the 44 patients, 67% were prerenal, 24% were renal, and 9% were postrenal. In all, 33% had stage 1 acute kidney injury, 27% had stage 2, and 40% had stage 3.

Results from the Integrated Biomedical Technology dipstick test correlated with the blood levels across all kidney injury stages and etiologies (P < .001).

The optimal diagnostic threshold levels for saliva were 25-34 mg/dL and 72 mg/dL for the blood measurement.

"In our study, we found good agreement between saliva and blood urea nitrogen at all stages of acute kidney injury in addition to a good diagnostic performance to discriminate between higher levels of blood vs lower values," Dr. Calice da Silva told Medscape Medical News.

"We also were able to diagnose up to AKIN 3 [Acute Kidney Injury Network stage 3] vs earlier stages, regardless of etiology of acute kidney injury," she said. "This implies the ability of the dipstick to identify those in need of more intensive care and possibly of immediate dialysis."

Patent Pending

A patent for the dipstick is pending, and the device is not yet approved by the US Food and Drug Administration. When it is available, the cost will be about $1, Dr. Calice da Silva said.

"Considering the costs to install a laboratory and medical infrastructure, a clear advantage becomes obvious," she noted.

Saliva urea nitrogen levels have been well documented in the past to correlate with blood levels; however, efforts to develop technology such as the dipstick have been hampered by drawbacks in accuracy or a lack of sensitivity.

The new technology involves a testpad containing urease, which cleaves to the urea to form hydroxyl ions, causing a pH change that results in changes in the colors on strips on the testpad. The intensity of the strip color corresponds to the levels of urea in saliva.

The availability of a saliva dipstick to help detect acute kidney injury could have global implications, said Jorge Cerda, MD, from the Albany Medical College and Capital District Renal Physicians, in New York.

"This could be very important in terms of its impact around the world," he told Medscape Medical News.

"In some regions of India or Africa, for instance, if you suspect kidney injury, all you can do is see if the patient is urinating or not," Dr. Cerda pointed out. "So this one-spot, simple, no-blood-draw test could truly revolutionize the management of early diagnosis of acute kidney injury and allow for early intervention."

On a broader level, improved diagnosis could help give a more accurate picture of kidney injury around the world.

"The incidence of acute kidney injury in low-to-middle-income countries may appear to be very low ― lower than developed countries," Dr. Cerda said, "but we don't think that's true. It's more likely that it is underreported."

Dr. Calice da Silva reports no relevant financial relationships. Her coauthors report financial ties with Fresenius Medical Care, RoFAR, Roche, Aethlon, Fibrogen, Affymax, Baxter, Genzyme, and Abbott. Dr. Cerda has disclosed no relevant financial relationships.

Kidney Week 2013: the American Society of Nephrology 46th Annual Meeting. Abstract FR-PO001. Presented November 8, 2013.

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