Consensus Between Osmolarity And Specific Gravity In Career Firefighters

BACKGROUND: Firefighters(FFs) are exposed to heat stress and physically demanding tasks, making hydration status a critical performance and safety factor. Although saliva osmolarity(Sosm) and urine specific gravity(USG) are the standard measures of hydration level, limited research exists on the relationship between the two metrics. Purpose: Thus, this study examined the relationship between Sosm and USG in career FFs. METHODS: Sosm and specific gravity data points were extracted from an annual health and fitness assessment. After a 24-hour shift, a cohort of 55 career FFs (age = 31.2 ± 9.6 years; experience = 8.2 ± 8.1 years) from a southeastern US fire department participated in this study. FFs reported to the university laboratory and refrained from consuming liquids ≥5 minutes prior to Sosm testing(MX3), then provided a urine sample for a USG measure (Master Refractometer by Atago). The measured hydration level was converted into hydration categories. Weighted Cohen’s Kappa was calculated to estimate the agreement of the two hydration tests. RESULTS: Results from Sosm test indicated 27 (49.1%) of the FFs were well hydrated, 21 (38.1%) mildly dehydrated, 6 (10.9%)significantly dehydrated, and 1 (1.8%) seriously dehydrated; proportions for USG were 23.6%(n = 13), 54.5% (n = 30), 18.2% (n = 10), and 3.6% (n = 2), respectively. The Weighted Cohen's kappa for agreement between the two tests was 0.05 (Standard Error = 0.09). CONCLUSIONS: Most subjects were mildly too seriously dehydrated according to either Sosm or USG, and results found minimal agreement between Sosm and USG. However, due to the convenience of Sosm testing, this method is recommended to gain insight into FF hydration status when compared to USG.