26624 PrecivityAD2, Plasma (C2AD2)

AB42/40 Ratio; Alzheimer's; Amyloid Beta; Amyloid Probability Score2; APOE; Dementia; Mild cognitive impairment; p-tau217; p-tau217 Ratio; Percent p-tau217; %p-tau217; C2N​

​The PrecivityAD2 blood test measures amyloid beta (Abeta) 42/40 ratio and percent tau phosphorylated at threonine-217 (%p-tau217). The results are then combined and used in a proprietary statistical algorithm to calculate the Amyloid Probability Score 2 (APS2). The APS2, Abeta 42/40 ratio and %p-tau217 are reported, however, individual Abeta42, Abeta40, phosphorylated tau217 and non-phosphorylated tau217 concentrations are not reported.

​Assisting in the evaluation of adult patients, aged 55 years and older, with signs or symptoms of mild cognitive impairment or dementia who are being assessed for Alzheimer disease and other causes of cognitive decline​

This is not intended for patients younger than 55 years, or for use as a screening test in patients without signs or symptoms of cognitive impairment, or for serial testing for assessment of longitudinal changes.

​Contact Lab Specimen Processing at 715-224-6220 or 800-222-5835 to obtain special aliquot tubes (See Step 2 below). 

1. Centrifuge within two hours of collection.

2. Label two 2-mL screw-cap micro tubes. (Screw cap micro tube, 2 mL, PCR Performance Tested, Low protein-binding (T983))

3. Aliquot 1.5 mL of plasma into each labeled micro tube.

4. Freeze plasma (no longer than 2 hours after collection) at or below -20 degrees C.

5. Place labeled aliquot tubes inside a larger tube or vial for transport.

6. Specimens must be shipped frozen on dry ice.

​Gross hemoylsis; Gross lipemia; Gross icterus; Outside of age range; Specimen collected outside of testing range (too long in storage before arrival to testing facility); Insufficient volume; Incorrect labeling

​​This test is not a standalone test; Positive or negative APS2 values alone neither rule in nor rule out a diagnosis of Alzheimer disease (AD).​

Test results should be used in conjunction with other diagnostic tools, such as neurological examination, neurobehavioral tests, imaging, and routine laboratory tests.

False-positive and false-negative test results may occur.

This test uses interpretive data that were derived from clinical studies in a predominantly White US population of patients with mild cognitive impairment or early dementia. The extent of the differences in results (if any) based on individuals of other racial and ethnic groups has not yet been firmly established.

Currently, there is insufficient evidence to support serial testing for the assessment of longitudinal changes in biomarkers, including monitoring response to therapy.

The results of other analyte tests using other methodologies cannot be interpreted in the context of the PrecivityAD2 test.

​Alzheimer disease (AD) is defined pathologically by the presence of amyloid plaques and neurofibrillary tangles in the brain. Clinical characteristics include gradual onset of mild cognitive impairment (MCI), behavioral changes such as apathy, withdrawal, or agitation, and disease progression to middle and later stage dementia. Currently, no test detects AD with 100% accuracy; definitive diagnosis occurs at brain autopsy.​

Recent availability of anti-amyloid therapies increases the importance of detection of AD at an early stage. MCI impacts 12 to 18% of people in the United States over age 60 and is often an initial clinical sign of AD. Establishing or excluding an AD diagnosis with a high degree of certainty at first signs of memory decline may optimize medical management.

Brain amyloid pathology is detectable by amyloid positron emission tomography (PET) scan, cerebrospinal fluid testing, or liquid chromatography tandem mass spectrometry blood biomarker testing with high sensitivity and specificity in patients with MCI and early dementia. In all testing modalities, healthcare providers interpret test results in the context of the patient's clinical findings and other clinical work-up, as the neuropathological changes associated with AD can be seen in other forms of dementia and in unaffected individuals.

The PrecivityAD2 test is an analytically and clinically validated blood test that aids healthcare providers in ruling in or ruling out AD in patients presenting with MCI or dementia. This evaluation simultaneously quantifies specific plasma amyloid beta (Abeta) and tau peptide concentrations to calculate the Abeta42/40 ratio and percent tau phosphorylated at threonine-217 (%p-tau217). The inclusion of plasma analyte ratios has been shown to mitigate the effects of confounding factors such as chronic kidney disease. The ratios are combined into a proprietary statistical algorithm to calculate the Amyloid Probability Score 2 (APS2), a numerical value ranging from 0 to100 that determines whether a patient is positive (has high likelihood) or negative (has low likelihood) for the presence of brain amyloid plaques by amyloid PET scan.

​The Amyloid Probability Score 2 (APS2) result is a composite score ranging from 0 to 100 that demonstrates the strongest correlation with brain amyloid pathology compared to the individual biomarkers (amyloid beta [Abeta] 42/40 ratio or percent tau phosphorylated at threonine-217 [%p-tau217]) considered separately. Discordance of the individual biomarkers can occur.​

Table. Amyloid Probability Score and Interpretation

The APS2 result should be interpreted in conjunction with other patient information. Clinical correlation is recommended.