Studied since the early 1990s, cerebrospinal fluid Aβ42 is the most established fluid marker for detecting early Alzheimer’s disease, yet trying to turn it into a clinically certified, broad-based test has been a bear. Variability at all levels has beset the effort, and standard cutoffs for Aβ42 positivity have remained elusive. Now, scientists at the European Commission’s Joint Research Centre (JRC) have announced that in collaboration with the International Federation of Clinical Chemistry and Laboratory Medicine, they have overcome a major hurdle that will make assays robust and reliable for clinical practice.
- Scientists have taken another step toward standardizing Aβ assays.
- They collected and pooled CSF samples and measured their Aβ42 content.
- Companies can now calibrate existing and future immunoassays to this standard.
They have developed three certified reference materials (CRM), which consist of pooled CSF samples with low, medium, and high concentrations of Aβ42, for wide distribution. “These materials will make it possible for kit manufacturers to calibrate their assays to the CRMs,” wrote Henrik Zetterberg, University of Gothenburg, Sweden, to Alzforum. “The effect will be that different assays will give similar results, which will allow laboratories to harmonize their cutoffs and reference limits. This will make the tests more widely used on a global basis, especially to support diagnosis-making in clinical practice.”
Zetterberg helped develop the CRMs, which was the second of two steps required for a calibration hierarchy (Oct 2015 news). The first involved settling on a definitive measurement protocol to set the value of Aβ42 in a future CRM. In 2015, researchers settled on using liquid chromatography tandem mass spectrometry (LC-MS/MS; see Leinenbach et al., 2014; Korecka et al., 2014). With the protocol in hand, they next had to generate the CRM.
Scientists led by Ingrid Zegers at the JRC and Kaj Blennow at the University of Gothenburg collected CSF from 24 patients with normal-pressure hydrocephalus whose excess CSF was continuously drained from their brains to relieve pressure. The researchers then measured the Aβ42 from each sample and combined those that had low, medium, or high levels of the peptide. After thoroughly homogenizing all three pools of CSF, they aliquoted them into 0.5 mL vials and froze them for storage.
Multiple labs from Europe and the U.S. independently completed LC-MS/MS on several thawed samples, and agreed on reference values of 0.45, 0.72, and 1.22 μg/L of Aβ42 for the low, medium, and high samples, respectively. These CRMs are now available worldwide for companies and research groups that want to calibrate their methods. This will allow the end users of their commercialized tests—hospitals, doctors, research groups, clinical trials centers—to compare results across tests and labs.
“It will take some time before the manufacturers of the test kits have recalibrated their assays to the reference system, which consists of a combination of the reference methods and the reference materials,” Zegers wrote to Alzforum. “After that is done they could possibly agree on a common cutoff.”
“This will definitely be a major step toward a more general use of these diagnostic tests,” wrote Blennow to Alzforum. Fully automated measurement methods and routine use by physicians of lumbar puncture will give yet another boost, he added, as will amyloid-targeting treatments coming to market, said Zetterberg.—Gwyneth Dickey Zakaib
- Leinenbach A, Pannee J, Dülffer T, Huber A, Bittner T, Andreasson U, Gobom J, Zetterberg H, Kobold U, Portelius E, Blennow K, IFCC Scientific Division Working Group on CSF proteins. Mass spectrometry-based candidate reference measurement procedure for quantification of amyloid-β in cerebrospinal fluid. Clin Chem. 2014 Jul;60(7):987-94. Epub 2014 May 19 PubMed.
- Korecka M, Waligorska T, Figurski M, Toledo JB, Arnold SE, Grossman M, Trojanowski JQ, Shaw LM. Qualification of a surrogate matrix-based absolute quantification method for amyloid-β₄₂ in human cerebrospinal fluid using 2D UPLC-tandem mass spectrometry. J Alzheimers Dis. 2014;41(2):441-51. PubMed.
- Doecke JD, Rembach A, Villemagne VL, Varghese S, Rainey-Smith S, Sarros S, Evered LA, Fowler CJ, Pertile KK, Rumble RL, Trounson B, Taddei K, Laws SM, Macaulay SL, Bush AI, Ellis KA, Martins R, Ames D, Silbert B, Vanderstichele H, Masters CL, Darby DG, Li QX, Collins S, AIBL Research Group. Concordance Between Cerebrospinal Fluid Biomarkers with Alzheimer's Disease Pathology Between Three Independent Assay Platforms. J Alzheimers Dis. 2018;61(1):169-183. PubMed.
- Janelidze S, Pannee J, Mikulskis A, Chiao P, Zetterberg H, Blennow K, Hansson O. Concordance Between Different Amyloid Immunoassays and Visual Amyloid Positron Emission Tomographic Assessment. JAMA Neurol. 2017 Dec 1;74(12):1492-1501. PubMed.
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