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HelpTest Code AMYR Beta-Amyloid Ratio (1-42/1-40), Spinal Fluid
Ordering Guidance
This test is intended for use in adult patients aged 55 years and older. If evaluating an individual 54 years or younger, order ADEVL / Alzheimer Disease Evaluation, Spinal Fluid.
This test only measures the beta-amyloid ratio (1-42/1-40) in cerebrospinal spinal fluid. Individual beta-amyloid 1-42 and 1-40 concentrations are not reported. If measurement of additional neurodegeneration markers such as total Tau, phosphorylated Tau (p-Tau181), beta-amyloid (1-42), and the p-Tau/beta-amyloid 42 ratio are desired, order ADEVL / Alzheimer Disease Evaluation, Spinal Fluid.
Specimen Required
Container/Tube:
Preferred: Sarstedt 1.5 mL tube (Ref. 72.703.600), Collect at least 750 mcL of cerebrospinal spinal fluid (CSF) or (≥50% full).
Acceptable: Sarstedt CSF False Bottom Tube 63.614.625 (2.5 mL), Sarstedt 72.694.600 (2 mL) or Sarstedt 10 mL tube Ref. 62.610.018 (Collect at least 5 mL of CSF [≥50% full]).
All tubes should be filled to between 50% to 100% of the total empty container volume. Specimens received with less than the required fill volume may be rejected.
Specimen Volume: 0.75 to1.5 mL or at least 50% container volume
Collection Instructions:
1. This test is intended for use in adult patients, aged 55 years and older. Do not collect CSF for this test if the patient is younger than 55 years of age.
2. Perform lumbar puncture and discard the first 1 to 2 mL of CSF. Note: CSF collection should be performed by the gravity drip method.
3. Discard any visibly blood contaminated CSF.
4. Collect CSF directly into one of the listed collection tubes until the tube is at least 50% full.
5. If transporting frozen, freeze sample upright prior to placing in transport container.
6. If transporting refrigerate, tubes should be transported upright.
Note: Polystyrene collection tubes are not acceptable. Exposure of CSF to polystyrene tubes may result in falsely low beta-amyloid concentrations. For more information see Cautions.
7. Collection instructions can also be found on Spinal Fluid Specimen Collection Instructions for B-Amyloid (1-42/1-40) (T979).
Useful For
Assisting in the evaluation of adult patients, aged 55 years and older, presenting with cognitive impairment and are being assessed for Alzheimer disease and other causes of cognitive decline
This test is not intended as a screening or stand-alone diagnostic assay.
Method Name
Chemiluminescent Immunoassay/Calculation
Reporting Name
Beta-Amyloid Ratio (1-42/1-40), CSFSpecimen Type
CSFSpecimen Minimum Volume
See Specimen Required
Specimen Stability Information
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| CSF | Frozen (preferred) | 90 days | |
| Refrigerated | 14 days | ||
| Ambient | 48 hours |
Reference Values
Beta-Amyloid Ratio (1-42/1-40): ≥0.073
Interpretation
A normal beta-amyloid ratio (1-42/1-40) of 0.073 and above is consistent with a negative (normal) amyloid positron emission tomography (PET) scan result. This result indicates a reduced likelihood that a patient's cognitive impairment is due to Alzheimer disease (AD).
A beta-amyloid ratio (1-42/1-40) between 0.059 and 0.072 (likely positive) is more likely consistent with a positive amyloid PET scan result. A likely positive result does not establish a diagnosis of AD or other cognitive disorder and has increased uncertainty in regard to amyloid PET positivity.
An abnormal beta-amyloid ratio (1-42/1-40) of 0.058 and below is consistent with a positive (abnormal) amyloid PET scan result. This result does not establish a diagnosis of AD or other cognitive disorder.
The performance of the beta-amyloid ratio (1-42/1-40) compared to amyloid PET is shown below and described as amyloid PET-positive predictive value (indicated as Predictive Value: PV):
Table.
|
Beta-amyloid ratio (1-42/1-40) |
Amyloid PET |
||||
|
Positive (n=199) |
Negative (n=93) |
Total (n=293) |
Amyloid PET-positive PV, % |
95% CI, % |
|
|
Positive (abnormal) (ratio ≤0.058) |
171 |
6 |
177 |
96.6 |
92.8-98.4 |
|
Likely positive (ratio 0.059 to 0.072) |
13 |
9 |
22 |
59.1 |
38.7-66.7 |
|
Negative (ratio ≥0.073) |
15 |
78 |
93 |
16.1 |
10.0-24.9 |
Clinical Reference
1. Wiltfang J, Esselmann H, Bibl M, et al. Amyloid beta peptide ratio 42/40 but not A beta 42 correlates with phospho-Tau in patients with low- and high-CSF A beta 40 load. J Neurochem. 2007;101(4):1053-1059. doi:10.1111/j.1471-4159.2006.04404.x
2. Dumurgier J, Schraen S, Gabelle A, et al. Cerebrospinal fluid amyloid-beta 42/40 ratio in clinical setting of memory centers: a multicentric study. Alzheimers Res Ther. 2015 ;7(1):30. doi:10.1186/s13195-015-0114-5
3. Gervaise-Henry C, Watfa G, Albuisson E, et al. Cerebrospinal fluid ABeta42/ABeta40 as a means to limiting tube- and storage-dependent pre-analytical variability in clinical setting. J Alzheimers Dis. 2017;57(2): 437-445. doi:10.3233/JAD-160865
4. Toombs J, Foiani MS, Wellington H, et al.Amyloid Beta peptides are differentially vulnerable to preanalytical surface exposure, an effect incompletely mitigated by the use of ratios. Alzheimers Dement (Amst). 2018;10:311-321. doi:10.1016/j.dadm.2018.02.005
5. Delaby C, Munoz L, Torres S, et al. Impact of CSF storage volume on the analysis of Alzheimer's disease biomarkers on an automated platform. Clin Chim Acta. 2019;490:98-101. doi:10.1016/j.cca.2018.12.021
Day(s) Performed
Thursday
Report Available
1 to 7 daysPerforming Laboratory
Mayo Clinic Laboratories in Rochester
Test Classification
This test has been cleared, approved, or is exempt by the US Food and Drug Administration and is used per manufacturer's instructions. Performance characteristics were verified by Mayo Clinic in a manner consistent with CLIA requirements.CPT Code Information
0358U
LOINC Code Information
| Test ID | Test Order Name | Order LOINC Value |
|---|---|---|
| AMYR | Beta-Amyloid Ratio (1-42/1-40), CSF | 98485-6 |
| Result ID | Test Result Name | Result LOINC Value |
|---|---|---|
| 4240R | Beta-Amyloid Ratio | 98485-6 |
| AMYIN | Beta-Amyloid Ratio Interpretation | 69048-7 |
Forms
If not ordering electronically, complete, print, and send a Neurology Specialty Testing Client Test Request (T732) with the specimen.