11 Apr 2025
A new era in the evaluation of Alzheimer's disease
The pathological hallmarks of Alzheimer’s disease (AD) are extracellular amyloid plaques consisting of aggregated beta amyloid (AB) peptides1 and intracellular neurofibrillary tangles containing abnormally phosphorylated tau (p-tau).2 Identification of these pathologies, particularly amyloid, is necessary for a clinical diagnosis of AD. Advancements in high-sensitivity immunoassay platforms have enabled blood-based biomarkers to be effective and accurate tools in the evaluation of individuals being evaluated for possible AD.
pTau-217/Beta Amyloid 42 Ratio
Intended Use: In the context of all clinical findings in individuals presenting with cognitive impairment, the pTau-217/Beta Amyloid 42 Ratio can aid in the identification of amyloid-related pathology, which is associated with Alzheimer’s disease. This test is not intended as a screening test for Alzheimer’s disease in asymptomatic individuals.
Assay Performance:
- The combination of pTau-217 and AB42, in ratio, demonstrates a higher level of sensitivity and specificity than Beta Amyloid 42/40 Ratio or pTau-217 alone
- pTau-217/Beta Amyloid 42 Ratio performance demonstrates a sensitivity of 95% and specificity of 95% based on 200 samples from a cohort of well-studied individuals in which all samples were characterized with patient age, sex, amyloid positron emission tomography (PET) status, and clinical diagnosis
pTau-217/Beta Amyloid 42 Ratio meets the performance criteria established by an international consortium as a confirmatory blood test that is equivalent to cerebrospinal fluid assays and amyloid-PET imaging measures3
| Triage Test | Confirmatory Test | |
|---|---|---|
| Global CEOi performance criteria3 |
Sensitivity ≥90% Specificity ≥ 75–85%, depending on capacity for follow-up amyloid PET or CSF testing3 For a test with two cutoffs, <20% of individuals should have an intermediate result |
Sensitivity ≥90% Specificity ≥90% For a test with two cutoffs, <20% of individuals should have an intermediate result |
| Labcorp test performance |
Sensitivity: 95% Specificity: 84% Beta-Amyloid 42/40 Ratio (505725) Sensitivity: 96% Specificity: 87% |
pTau-217/Beta Amyloid 42 Ratio (505415) Sensitivity: 95% Specificity: 95% |
Assay sensitivity and specificity is dependent on pathological characteristics of study cohort
Interpretation
| Result | Reference Interval | Comment |
|---|---|---|
| Low | < 0.0086 | A low ratio is consistent with a negative (normal) amyloid-positron emission tomography (PET) scan result. This result aids in the exclusion of amyloid-related pathology associated with Alzheimer disease. |
| Intermediate | 0.0086 – 0.0152 | An intermediate pTau-217/Beta Amyloid 42 Ratio should be interpreted within the context of all clinical findings. Additional testing such as amyloid positron emission tomography imaging and cerebrospinal fluid biomarkers assays are recommended to aid in the identification of amyloid-related pathology. |
| High | 0.0152 | A high ratio is consistent with a positive (abnormal) amyloid-positron emission tomography (PET) scan result. This result aids in the identification of amyloid-related pathology associated with Alzheimer disease. In the proper clinical context this test is supportive of Alzheimer disease being related to current clinical symptoms. |
| Test Name | Test No. | Turnaround Time | Specimen | Container |
|---|---|---|---|---|
| Phosphorylated Tau 217 (pTau-217)/Beta Amyloid 42 Ratio | 505415 | 5-7 days | 1 mL plasma, frozen | Lavender-top (EDTA) tube |
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References
1. Iwatsubo T, Odaka A, Suzuki N, Mizusawa H, Nukina N, Ihara Y. Visualization of Aβ42 (43) and Aβ40 in senile plaques with end-specific Aβ monoclonals: evidence that an initially deposited species is Aβ42 (43). Neuron. 1994;13(1):45-53. doi:10.1016/0896-6273(94)90458-8
2. Perl DP. Neuropathology of Alzheimer’s disease. Mt Sinai J Med. 2010;77(1):32-42. doi:10.1002/msj.20157
3. Schindler SE, Galasko D, Pereira AC, et al. Acceptable performance of blood biomarker tests of amyloid pathology — recommendations from the Global CEO Initiative on Alzheimer’s Disease. Nat Rev Neurol. 2024;20(7):426-439. doi:10.1038/s41582-024-00977-5