Probability of Amyloid Positivity

Calculation tool
About the test

Results

Without biomarker

With plasma p-tau

Age:

year
Clinical diagnosis:
Plasma p-tau217:

Insert patient data

Age: year

Clinical diagnosis

Note: Data on the pretest prevalence of amyloid pathology in this syndrome for this age group are not available

Assay

Plasma p-tau217 (Mesoscale Discovery) Plasma p-tau181 (Quanterix Simoa)

Result

Negative Positive

Value:

Reference

1. Jansen WJ, Janssen O, Tijms BM, et al. Prevalence Estimates of Amyloid Abnormality Across the Alzheimer Disease Clinical Spectrum. JAMA Neurol. 2022;79(3):228-43.

2. Ossenkoppele R, Jansen WJ, Rabinovici GD, et al. Prevalence of amyloid PET positivity in dementia syndromes: a meta-analysis. JAMA. 2015;313(19):1939-49.

3. Grimes DA, Schulz KF. Refining clinical diagnosis with likelihood ratios. Lancet. 2005;365(9469):1500-5.

Thai Red Cross Emerging Infectious Diseases Health Science Centre, King Chulalongkorn Memorial Hospital

Disclaimer

The calculation tool is to be used by clinicians for educational purposes only

About the test

Plasma p-tau217 in this calculation tool is measured on the Mesoscale Discovery platform with the S-PLEX Human Tau (pT217) Kit. Plasma p-tau181 values are obtained using the Quanterix pTau-181 V2.1 Advantage - Version 1, transformed to fit the previously published values (Thanapornsangsuth, 2023). The reference values for amyloid status determination (or AD CSF profile) were extrapolated from real-world patients across the AD continuum at King Chulalongkorn Memorial Hospital, Bangkok, Thailand who underwent amyloid PET or CSF analysis.

With the current memory clinic database, plasma p-tau217 had an AUC of 0.96 for determining amyloid positivity. The optimal cut-off value is 7.69 pg/mL as it has the greatest Youden’s index. Using this threshold, plasma p-tau217 has the sensitivity and specificity of 90.3% and 92.0%, respectively. The diagnostic parameters for plasma p-tau181 are as follows: AUC= 0.88; optimal cut-off= 2.89 pg/mL; sensitivity= 79.2%; specificity= 90.0%.

Reference

Thanapornsangsuth P, Booncharoen K, Luechaipanit W, et al. Prospective evaluation of plasma phosphorylated tau in a real-life memory clinic in Thailand. Alzheimers Dement. 2023;19(6):2745-2749.