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Test 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), CSF

Specimen Type

CSF

Specimen 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

Reject Due To

Gross hemolysis Reject
Gross lipemia Reject
Gross icterus Reject

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

Day(s) Performed

Thursday

Report Available

1 to 7 days

Performing 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.