Screening for Addison’s Disease in the Kalahari Desert: Field Use of a Smartphone Point-of-Care Salivary Cortisol Immunoassay

Presentation Number: MON 383
Date of Presentation: April 3rd, 2017

Joel R L Ehrenkranz*1 and Polly Wiessner2
1Intermountain Healthcare, Murray, UT, 2Arizona State University, Tempe, AZ

Abstract

Tuberculis destruction of the adrenal glands is the most common cause of Addison’s disease worldwide. Many patients with active tuberculosis lack access to facilities that are able to measure cortisol and, as a result, patients in rural and remote areas are at risk of death from undiagnosed acute adrenal insufficiency. This study was conducted among the San people, an indigenous tribe of hunter-gathers who reside in the Kalahari Desert in Namibia. Tuberculosis is endemic among the San and explained deaths in patients with tuberculosis is not uncommon. One possible cause of death in the San with tuberculosis is acute adrenal insufficiency. There are, however, no laboratory methods for diagnosing this fatal complication of tuberculosis in this remote population.

We used a smartphone quantitative immunochromatographic cortisol assay to measure salivary cortisol in 15 patients (7 females, ages 8-68 and 8 males, ages 22-66) with active tuberculosis and in 33 controls (11 females, ages 21-48 and 22 males, ages 7-46). Patients with tuberculosis were receiving ethionamide and cycloserine. The cortisol assay uses a competitive lateral flow format in which the intensity of the test line on a nitrocellulose membrane is inversely correlated with the salivary cortisol concentration. A smartphone attachment is used to position and illuminate the lateral flow cortisol assay. The samrtphone camera images the test and uses an image analysis algorithm application (app) on the smartphone to quantify the test result. The smartphone cortisol immunoassay has a limit of detection of 0.03 mcg/dL, dynamic range of 0.05-1.5 mcg/dL, coefficient of variation < 20%, and no significant cross reactivity with other endogenous or exogenous steroids. Cortisol was measured in 10 minutes using 70 microliters of filtered saliva that was collected ½ hour after awakening. Saliva samples were stored at 4.5OC. and assayed within 24 hours of collection.

Female patients with active tuberculosis had mean salivary cortisol concentrations of 0.28 mcg/dL, male tuberculosis patients mean salivary cortisol levels were 0.40 mcg/dL. Mean salivary cortisol concentrations in female controls was 0.38 and 0.40 mcg/dL in male controls. There were no significant differences in salivary cortisol levels between the groups.

This study demonstrates the clinical utility of a smartphone point-of-care cortisol assay to provide access to basic endocrine diagnostics. Whether the observed trend in decreased salivary cortisol in patients with active tuberculosis, measured at the time of day when cortisol concentrations are physiologically maximal, represents a reliable index of adrenal function in patients at risk for Addison’s disease remains to be determined. Protocols for diagnosing acute adrenal insufficiency based upon the use of a smartphone point-of-care salivary cortisol immunochromatographic assay need to be developed and validated.

 

Disclosure: JRLE: Founder, i-calQ L.L.C.. Nothing to Disclose: PW