We monitored changes in salivary creatine pre- and post-high-intensity exercise in young adults while also investigating the potential correlation between salivary and serum creatine levels.

Saliva and serum samples were collected before and immediately after an incremental running-to-exhaustion treadmill test in fifteen young adults (mean age [23.9 ​± ​2.9] years, eight females), with samples analyzed for guanidinoacetic acid, creatine, and creatinine using a liquid chromatography–tandem mass spectrometry method.

Following exercise, there was a substantial elevation in salivary creatine levels from (17.5 ​± ​14.2) μmol·L⁻¹ to (43.6 ​± ​30.4) μmol·L⁻¹ (p ​< ​0.001), coupled with a significant increase in salivary creatinine from (11.3 ​± ​5.8) μmol·L⁻¹ to (17.0 ​± ​9.3) μmol·L⁻¹ (p ​= ​0.04). In contrast, serum creatine levels were unaffected by exercise (p ​= ​0.80), while creatinine levels exhibited a strong tendency to decrease post-exercise (from [81.8 ​± ​17.5] μmol·L⁻¹ to [73.1 ​± ​11.6] μmol·L⁻¹; p ​= ​0.06). A comparison of the slopes of the two regression lines (saliva vs. serum) revealed significant differences for both creatine (p ​= ​0.01) and creatinine (p ​= ​0.03).

The above findings suggest a potential difference in the dynamics of creatine metabolites in these two bodily fluids, both pre and post-exercise.