Reliability and minimal detectable change of the MX3 hydration testing system

• Published in: PloS one 2024-11, Vol.19 (11), p.e0313320
• Main Authors: Winter, Ian, Burdin, Josie, Wilson, Patrick B
• Format: Article
• Language: English
• Subjects: Adult; Biology and Life Sciences; Biomarkers; Body composition; Body fluid osmolality; Chemical properties; Confidence intervals; Consent; Correlation coefficient; Correlation coefficients; Data collection; Dehydration - diagnosis; Density; Dietitians; Drinking (Physiology); Engineering and Technology; Exercise; Female; Fluid intake; Health aspects; Humans; Hydration; Hypotheses; Investigations; Laboratories; Lower bounds; Male; Medicine and Health Sciences; Methods; Osmolar Concentration; Physical fitness; Physical Sciences; Reliability; Reproducibility of Results; Saliva; Saliva - chemistry; Saliva - metabolism; Salivary glands; secretions; Test procedures; Urine; Young Adult
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0313320

Assessing hydration status outside of laboratories can be challenging given that most hydration measures are invasive, stationary, costly, or have questionable validity. This study investigated the within-day, test-retest reliability, and minimal detectable change (MDC) of the MX3 Hydration Testing System (MX3 Diagnostics), a relatively low cost, noninvasive, and portable method to measure saliva osmolality. Seventy-five adults (44 men, 31 women; 29.6±10.8 yr, 171.1±9.2 cm, 79.1±15.4 kg) presented two saliva samples approximately 3 to 5 minutes apart. Fluid intake was avoided for at least 5 minutes prior to sample collections. For each sample collection, a researcher used the MX3 to tap the tip of a test strip to saliva on a participant's tongue. Intra-class correlation coefficients (ICCs) and MDC were calculated as measures of reliability. Means for the two measurements were 64.3±19.0 mOsm and 65.5±17.9 mOsm (mean difference of -1.2±13.0 mOsm; t = -0.806, p = 0.423). Further analysis with a two-one-sided test procedure revealed equivalence between the two SOSM measurements (p < 0.001 for upper and lower bounds). Within-day repeat measures yielded an ICC of 0.75 and an MDC at the 90% confidence level of 21.3 mOsm. With moderate-to-good reliability, the MX3 appears to be a practical choice for reliably measuring moderate-sized changes (>20 mOsm) in saliva osmolality outside of laboratory constraints.