A more efficient enzyme-linked immunosorbent assay for measurement of alpha-synuclein in cerebrospinal fluid.

We describe a modification of a previously described assay for the quantification of alpha-synuclein in naive cerebrospinal fluid, which allows for a more efficient quantification of alpha-synuclein. Detection limit of the assay is 3.8 ng/ml and the assay is linear until 300 ng/ml. Inter-assay and intra-assay coefficients of variation are below 15% in a wide range of concentrations. Mean recovery of the assay is 94%. The 95% upper limit of the reference range (p95) in a group of neurological controls above the age of 45 years is 62 ng/ml. This assay can be routinely applied for quantification of alpha-synuclein in cerebrospinal fluid, but not in serum, and this may serve as a possible biomarker for alpha-synucleinopathies such as Parkinson's disease and multiple system atrophy.

Rapid immunoassay for the determination of glial fibrillary acidic protein (GFAP) in serum.

BACKGROUND: This study was aimed to develop a sensitive and rapid assay for the determination of glial fibrillary acidic protein (GFAP) in serum and to evaluate the clinical applicability in serum samples from patients with acute stroke. METHODS: The two-site chemiluminometric immunoassay, intended to use in a near-patient setting with a single incubation step (20 min), was used to measure serum samples from healthy blood donors and from patients with brain injury and correlated to serum S100B levels. RESULTS: The GFAP assay covered a concentration range up to 18 microg/L with an analytical sensitivity of 0.014 microg/L. The intra-assay precision was 3.5% at 1.55 microg/L (n=20) and 4.1% at 0.39 microg/L (n=20). The inter-assay precision was 3.8% at 9.1 microg/L (n=10) and 10.3 % at 0.21 microg/L (n=9). Normal controls (n=46) showed non-detectable GFAP with a 99% upper limit of <0.04 microg/L. GFAP values were associated with progression and severity of the illness in acute stroke patients. CONCLUSIONS: We have developed an improved assay for the measurement of GFAP levels in serum. Serum GFAP is a potential marker for prognosis and outcome in patients with central nervous system disorders.

Measurement of glial fibrillary acidic protein in blood: an analytical method.

BACKGROUND: In the present study, a new assay for the measurement of glial fibrillary acidic protein (GFAP) in human blood is described. The aim of the study was to present the characteristics of a new GFAP assay for blood analysis. METHODS: The method, a newly developed enzyme-linked immunosorbent assay (ELISA), was validated using blood samples from healthy blood donors and from patients with severe traumatic brain injury (TBI). RESULTS: 22 out of 72 healthy blood donors had a detectable GFAP level. The reference values (percentiles) are as follows: P50=0.15 microg/l and P95=0.49 microg/l; range 0.15-0.76 microg/l. CONCLUSIONS: GFAP in blood might be a promising new marker for astrocyte involvement after acute brain damage.

Diagnostic accuracy of ELISA and xMAP technology for analysis of amyloid beta(42) and tau proteins.

BACKGROUND: Cerebrospinal fluid (CSF) concentrations of amyloid beta(42) (Abeta(42)) peptides and tau proteins may serve as biomarkers for Alzheimer disease (AD). Recently, the xMAP technology has been introduced as an alternative to ELISA for measurement of these markers. METHODS: We used xMAP assays and ELISA to analyze CSF concentrations of Abeta(42), total tau (t-tau), and tau phosphorylated at threonine 181 (p-tau(181)) in samples from 69 patients with Alzheimer disease, 26 patients with vascular dementia, and 55 controls without neurological disorders. RESULTS: High CV values (>28%) for the ratio of xMAP:ELISA were observed for each biomarker, indicating that a constant correction factor cannot be applied to recalculate xMAP results into ELISA results. When a combination of CSF markers was used, the sensitivity, specificity, and area under the ROC curves for xMAP assays and ELISAs were not significantly different in differentiating AD patients from vascular dementia patients and controls. CONCLUSIONS: A constant conversion factor cannot be used successfully to recalculate results obtained with xMAP assays to those from the ELISAs. With the use of analysis of a combination of Abeta(42), t-tau, and p-tau in CSF, however, differentiation of clinical groups is equivalent when either xMAP technology or conventional ELISA is used.