Test Details
Methodology
Roche Diagnostics Electrochemiluminescence Immunoassay (ECLIA)
Result Turnaround Time
2 - 5 days
Turnaround time is defined as the usual number of days from the date of pickup of a specimen for testing to when the result is released to the ordering provider. In some cases, additional time should be allowed for additional confirmatory or additional reflex tests. Testing schedules may vary.
Use
The Elecsys® pTau-181 plasma assay result is intended to be used as an aid in the initial assessment for Alzheimer's disease and other causes of cognitive decline in adult patients ages 55 years and older presenting with signs, symptoms or complaints of cognitive decline. The result should be interpreted in conjunction with other clinical information.
A negative test result is consistent with a negative amyloid positron emission tomography (PET) scan result and reduced likelihood that a patient's cognitive impairment is due to amyloid pathology. These patients should be investigated for other causes of cognitive decline.
A positive test result may not be consistent with a positive amyloid PET scan result. Patients with an initial positive result should be further investigated to determine whether the amyloid pathology can be a cause of cognitive impairment.
Specimen Requirements
Specimen
EDTA plasma
Volume
1 mL
Minimum Volume
0.7 mL (Note: This volume does not allow for repeat testing.)
Container
Lavender-top (EDTA) tube
Collection Instructions
Draw blood in lavender-top (EDTA) tube. Invert to mix with preservatives. Centrifuge and transfer plasma to a labeled plastic transport tube.
Stability Requirements
| Temperature | Period |
| Room temperature | 2 days (stability determined by manufacturer or literature reference) |
| Refrigerated | 7 days (stability determined by manufacturer or literature reference) |
| Frozen | 3 months (stability determined by manufacturer or literature reference) |
| Freeze/thaw cycles | Stable x1 (stability determined by manufacturer or literature reference) |
Reference Range
| pTau-181 result | Interpretation |
| Negative (≤0.722pg/mL) | A negative result is consistent with a negative amyloid PET scan result. These patients should be investigated for causes of cognitive decline other than amyloid pathology. |
| Positive (>0.722 pg/mL) | A positive result may not be consistent with a positive amyloid PET scan result. Patients with an initial positive result should be further investigated to determine whether amyloid pathology can be a cause of cognitive impairment. |
Storage Instructions
Room temperature
Causes for Rejection
Serum specimen; improper labeling