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New Smartphone App Measures Cortisol Levels at Point of Care

Test takes about 5 minutes

With a simple tube, some software, and a saliva sample, patients and their physicians can measure levels of the stress hormone cortisol, according to new research presented at ICE/ENDO 2014, the joint meeting of the International Society of Endocrinology and the Endocrine Society in Chicago, Illinois.

According to researchers at the University of Utah, the measurement of salivary cortisol by laboratory immunoassay or mass spectroscopy requires instrumentation and technical personnel and is unable to deliver timely results. They therefore developed a smartphone-based salivary cortisol immunoassay that provides results in 5 minutes and can be performed at the point of care.

While a commercial lab in the U.S. might charge up to $50 to run a quantitative salivary cortisol test, the smartphone test will cost under $5, lead investigator Dr. Joel Ehrenkranz told Reuters Health.

The device consists of a case, a light tube, and a lens; it uses no battery power; and it is unbreakable and reusable, Ehrenkranz said.

When performing an assay, a glass fiber element containing colloidal gold-labeled murine anti-cortisol antibodies and a saliva collection pad are inserted at the proximal end of a nitrocellulose membrane, and a wicking sump is placed at the membrane’s distal end. Samples of artificial saliva containing cortisol in concentrations of between 0.012 and 3.0 mcg/dL are deposited on the strip’s saliva collection pad. The assay strip is then inserted into a reader, which aligns a lens and light diffuser with a smartphone’s camera and flash, and the strip is imaged 5 minutes after the addition of the specimen.

A smartphone image analysis app identifies the control and test lines on the assay strip and quantifies the pixel density of the green color channel of the test-line image. An algorithm is then derived by fitting an exponential curve to a graph of observed-versus-reference salivary cortisol values, which converts the pixel density of the green color channel to a cortisol value.

According to the researchers, this smartphone-based immunochromatographic technology can measure cortisol with a detection limit sufficient to diagnose adrenal insufficiency and hypercortisolism, and to monitor physiologic variations in cortisol concentrations.

Measuring salivary cortisol at the point-of-care in 5 minutes using an inexpensive immunochromatographic assay, reader, and smartphone may obviate the need to presumptively treat patients for adrenal insufficiency, the investigators say, and makes cortisol assays available to regions of the world that currently lack access to this diagnostic test.

Sources: Reuters; July 4, 2014; and ICE/ENDO 2014; June 24, 2014.

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