Phospho‑Tau/Total‑Tau/A Beta42, CSF (Change effective as of 05/20/24: Refer to 3017653 in the May Hotline)

Also known as: PHOSPHO T

Clinical Use

Use

Measures cerebrospinal fluid biomarkers—phospho‑Tau (181), total‑Tau, and Aβ42—to calculate ratios (pTau181/Aβ42 and tTau/Aβ42) that align more closely with amyloid PET imaging and aid evaluation of Alzheimer’s disease and cognitive impairment in adults ≥55 years old. Interpretation should always be in context with clinical diagnostic evaluation and not used alone to establish diagnosis.

Special Instructions

Not provided.

Limitations

Failure to adhere to collection instructions, especially using inappropriate tubes (e.g., polystyrene), may result in falsely reduced Aβ42 concentrations and consequently elevated ratio values. The ratios are not validated for predicting dementia development or monitoring therapy response, and results should not be used alone to establish Alzheimer’s disease diagnosis.

Test Details

Methodology

Immunoassay (ECLIA)

Biomarkers

Unknown protein

Protein

pTau181/Aβ42 ratio

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

tTau/Aβ42 ratio

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

Result Turnaround Time

1-7 days

Specimen

Cerebrospinal Fluid

Volume

Not provided

Minimum Volume

Not provided

Collection Instructions

Perform lumbar puncture and discard first 1–2 ml of CSF; collect directly into low‑bind polypropylene false‑bottom CSF tube (ARUP Supply #58810 preferred). Avoid syringes/extension tubing. Fill ≥50% of tube. Freeze or refrigerate and send in original tube; do not refreeze refrigerated or thaw frozen specimens.