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

Table 3 Summary of studies on salivary calcium and parathyroid hormone for chronic kidney disease diagnosis

Ref.	Biomarker(s)	Sample size (CKD/control)	CKD stage(s)	Collection method	Statistical analysis	Correlation (r)	AUC	Assay type	Key findings	Limitations
Rodrigues et al[65], 2016	Calcium, PTH	60/37	Stage 5	Stimulated (paraffin chewing)	T-test, pearson, simple linear regression	Calcium: -0.13, PTH: 0.03	NR	Colorimetric	No significant correlation between serum and saliva	Small sample size
Rajolani et al[66], 2024	Calcium, PTH	29/0	NR	Spitting method	Paired t-test, pearson's correlation	NR	NR	Enzymatic	No significant serum-saliva correlation for calcium and PTH	Healthy controls are needed for better comparison

AUC: Area under the curve; CKD: Chronic kidney disease; NR: Not reported; PTH: Parathyroid hormone; ROC: Receiver operating characteristic.