Measurement of fasting salivary insulin and its relationship with serum insulin in children

BACKGROUND: Saliva is a useful sample as a source of hormones for the diagnosis of different diseases, particularly in pediatric patients and aged individuals, because saliva offers a noninvasive and stress-free alternative to serum collection. The aim of this study was to validate a salivary insulin method and to check its clinical application in pediatric patients. METHODS: Saliva samples were collected from 130 boys and 147 girls aged 6–14 years. Salivary and serum insulin levels were measured with the chemiluminescent automated method Access (Beckman Coulter, Brea, CA, USA). Serum blood glucose levels were measured with the glucose oxidase method in an autoanalyzer. RESULTS: The precision profile of the method was determined for six aliquots of different concentrations from pools of saliva, and the coefficients of variation (CV) were 2.4% for 1 μUI/ml, 4% for 0.5, 8.9% for 0.25, 19% for 0.12, 28% for 0.06, and 38% for 0.03 μUI/ml, being the functional sensibility (concentration corresponding to a 20% CV) 0.12 μUI/ml. Insulin recovery was 100.13%. Salivary insulin levels diminished 29.8% in samples stored during 7 days at 2–8 °C. Differences in insulin values were not observed when samples were stored at −20 °C during 7 days. The methods used to measure salivary and serum insulin correlated significantly (r=0.92, P<0.001). However, at levels of serum insulin >20 μUI/ml, this correlation declined (r=0.57, P=0.083). CONCLUSION: The proposed method for salivary insulin measurement showed convenient analytical characteristics.