Saliva as a non-invasive biomarker for chronic kidney disease: Challenges and potential in disease monitoring

Table 1 Comparison of saliva collection methods based on biomarker reliability, feasibility, and limitations

Collection method	Biomarker reliability	Feasibility	Major limitations
Spitting	High	Easy and patient-friendly	Inconsistent flow, variable technique
Passive drool	Moderate to high	Non-invasive, simple	Slow collection, risk of evaporation
Stimulated (paraffin chewing)	Moderate (flow-dependent dilution)	Simple, cost-effective	Contamination risk, requires compliance, time-sensitive processing
Stimulated (parotid)	Variable, biomarker-specific	Targeted gland sampling	Invasive, discomfort, specialized equipment needed
Oral rinse	Low (due to dilution)	Very easy and rapid	Dilution effect, unreliable concentrations
Salivette®	Moderate	Standardized device available	Absorption variability, potential contamination