Beta Amyloid 42/40 Ratio Plasma (505725)

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Turnaround Time: 5 Days
CPT Code:

83520 x 2

Test Type: 2 mL Plasma, Frozen


Use: The plasma A42/40 ratio is intended for use as an adjunct to diagnostic evaluations of Alzheimer's disease, including neurological and cognitive performance examinations and PET neuroimaging.

The diagnostic hallmarks of Alzheimer's disease (AD) are extracellular deposits of beta amyloid plaques and neurofibrillary tangles observed in the cortex and limbic brain region upon autopsy. The major molecular components of beta amyloid plaques and neurofibriiary tangles are beta amyloid 1-42 and tau protiens, respectively. The major beta amyloid metabolic products beta amyloid 1-42 and beta amyloid 1-40 are generated by beta and secretase enzymatic cleavage of the amyloid precursor protein (APP), with more hydrophobic beta amyloid 1-42 peptide aggregating to form amyloid plaques. Reduced concentrations of beta amyloid 42 in EDTA plasma are associated with increased retention of beta amyloid tracers in the brain beta amyloid plaques observed with positron emisson tomography (PET), and are inversely correlated. Low beta amyloid 42/40 ratios are more associated with patients having a clinical diagnosis of AD or beta amyloid PET positivity, whereas higher ratios are less associated with AD diagnosis or beta amyloid PET positivity.

Limitations: Samples that contain fibrin, red blood cells and other insoluble objects may lead to inaccurate results.

This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.

Methodology: Sysmex chemiluminescence enzyme immunoassay (CLEIA)


Collection Details:

Collection Instructions:

specimen: Plasma, frozen

Volume: 2 mL

Minimum Volume: 1 mL (Note: This volume does not allow for repeat testing.)

Container: Lavender-top (EDTA) tube

Collection: Draw full lavender-top (EDTA) tube of blood. Separate plasma from blood via centrifugation (>1500g for 10 minutes) within 40 minutes after blood collection. Transfer plasma to Labcorp polypropylene transport tube and seal.

Storage Instructions: Plasma sample may be stored for up to 24 hours at < -10°C (standard freezer) prior to placing in dry ice (for shipment), or samples may be stored in the refrigerator for up to 10 hours but then must be placed on dry ice for transport. All samples must be placed on dry ice for transport and must be maintained on dry ice or similar temperatures when reaching the local lab.