Blood contamination in salivary diagnostics: current methods and their limitations.

The use of saliva samples in clinical studies has increased. However, the diagnostic value of whole saliva is compromised in the presence of blood contamination, owing to the higher levels of analytes in blood compared with those in saliva. The aim of this study was to review the existing methods and their limitations for measuring the levels of blood contamination in saliva. A literature search was performed using Web of Science, SCOPUS, and PubMed databases and 49 articles dealing with salivary diagnostics and measurements of blood contamination were included. Five methods for measuring the degree of blood components in saliva were discussed, including "visual inspection", use of "strip for urinalysis", and detection of plasma proteins such as "hemoglobin", "albumin", and "transferrin". Each method has its limitations, and transferrin has been regarded as the most reliable and valid marker for blood contamination in saliva. However, transferrin in whole saliva may not be solely a product of blood, and its level in whole saliva can be influenced by several factors such as age, gonadal hormones, salivary flow rate, chewing performance, and oral microorganisms. In conclusion, when quantitatively analyzing whole saliva samples, the influence of blood contamination should be considered.