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Laboratory-specific reference values for cerebrospinal fluid (CSF) Alzheimer disease (AD) biomarkers are necessary. Our objective was to apply well-known CSF biomarkers and redetermine their diagnostic cutoff values for AD in South Korea. CSF samples from matched control subjects (n=71), patients with AD dementia (ADD, n=76), and other neurological disorders with cognitive decline (OND, n=47) were obtained from 6 Korean dementia clinics according to a standardized protocol. CSF biomarker concentrations were measured using enzyme-linked immunosorbent assay. CSF biomarkers differed significantly between the ADD and control groups (P<0.001 for all), and between the ADD and OND groups (P<0.001 for all). The areas under the curve in differentiation of ADD from control subjects were 0.97 for Aβ42, 0.93 for total tau (tTau), 0.86 for pTau, and 0.99 for both tTau/Aβ42 and pTau/Aβ42 ratios. Our revised cutoff value for Aβ42 was higher than our previous one, whereas the values for the Tau proteins were similar. The tTau/Aβ42 ratio had the highest accuracy, 97%. Our findings highlight the usefulness of CSF AD biomarkers in South Korea, and the necessity of continually testing the reliability of cutoff values.

Background: Although plasma amyloid-β (Aβ) levels have been evaluated as a possible diagnostic marker of Alzheimer's disease (AD), the findings are inconsistent.Objective: The present study aimed to validate plasma levels of Aβ40, Aβ42, and the Aβ40/Aβ42 ratio as biomarkers of AD in subjects with early-onset AD (EOAD) without familial AD genetic mutations.Methods: Patients with sporadic EOAD (sEOAD) were prospectively recruited by nine neurology clinics. Plasma levels of Aβ40 and Aβ42 were measured using a sandwich enzyme-linked immunosorbent assay (ELISA) in 100 sEOAD (50-69 year-old) and 46 age-matched normal control subjects (50-72 year-old). Cerebrospinal fluid (CSF) was obtained from 32 sEOAD subjects and 25 controls. The integrity of the blood-brain barrier was assessed using the CSF/plasma albumin ratio.Results: The plasma levels of Aβ42 were significantly lower, while the Aβ40/Aβ42 ratio was significantly higher in sEOAD patients than in controls. The levels of Aβ40, Aβ42, and the Aβ40/Aβ42 ratio did not differ in relation to the APOEɛ4 allele. The CSF/plasma albumin ratio was comparable between the two groups, and the plasma parameters of Aβ proteins were not significantly associated. A multivariate analysis revealed that an increased Aβ40/Aβ42 ratio is valuable for the discrimination of sEOAD from controls (β=0.344, p=0.000). The area under the ROC curve for the Aβ40/Aβ42 ratio was 0.76, and a cut-off ratio of 5.87 was suggested to have 70% sensitivity and 68% specificity.Conclusion: The plasma Aβ40/Aβ42 ratio had moderate validity for the discrimination of sEOAD patients from age-matched controls. [ABSTRACT FROM AUTHOR]