Plasma β-amyloid1-42 reference values in cognitively normal subjects

Background In clinical practice, the use of plasma beta-Amyloid1-42 (A beta(1-42)) as biomarker for Alzheimer's disease is largely limited by the absence of reference values. The aim of this study was to evaluate A beta(1-42) plasma concentrations in cognitively normal subjects and to propose reference values. Methods Plasma samples were obtained from 245 subjects, with a wide age-range (19-89 years), enrolled at the Unit of Laboratory Medicine of the Azienda Ospedaliera Cardinale G. Panico (younger subjects) and from a population-based study on aging (GreatAGE study) (older subjects). Three different age-groups were established: young (<= 34), adult (35 <= age <= 64) and old (> 64). The Innogenetics Elisa kit for plasma A beta(1-42) was used for the analysis. Results The mean (SD) concentration of plasma A beta(1-42) was 17.65 (5.71) pg/mL. A positive trend was found in A beta(1-42) levels across the three age groups (p < .0001): young subjects showed values of A beta(1-42) significantly lower than the adult group (p < .0001) and than the old one (p < .0001 overall); no significant differences were found between the adult and the old groups (p = 1.0000). For the entire cohort the lower limit of 90% Reference Interval, double-sided, was 8.12 pg/mL (95% CI 6.77-9.45) and the upper limit was 29.00 pg/mL (95% CI 27.01-31.00). Conclusion The present study proposes reference values for plasma A beta(1-42). Nevertheless, further studies are needed to confirm these results and corroborate the use of these reference values in clinical practice.