Blood Test for CSF from Nose
β2-transferrin analysis is the definitive laboratory test to confirm that watery nasal discharge is cerebrospinal fluid, with near 100% specificity and high sensitivity. 1
Primary Diagnostic Test
β2-transferrin testing should be ordered as the first-line laboratory assay for any patient presenting with suspected CSF rhinorrhea, as recommended by the American College of Radiology. 1
This test demonstrates near-perfect specificity (approaching 100%) and high sensitivity, making it the gold standard for distinguishing CSF from normal nasal secretions or other fluids. 1, 2
β2-trace protein analysis serves as an alternative confirmatory test with comparable diagnostic accuracy to β2-transferrin. 2
Critical Collection Requirements
The patient must have active nasal drainage at the time of specimen collection for accurate results. 1
For intermittent leaks, multiple samples should be obtained during episodes of active rhinorrhea to avoid false-negative results. 1
Collect sufficient fluid volume for analysis; if inadequate fluid can be obtained, proceed directly to imaging-based confirmation (see below). 1
Tests to Avoid
Do not use glucose oxidase testing (glucose detection) as a confirmatory test despite its historical use as a screening method. 3
Glucose testing has unsatisfactory sensitivity and specificity, with false-negative results occurring from bacterial contamination and false-positive results common in diabetic patients. 3
Algorithm After Positive β2-Transferrin
Once β2-transferrin confirms CSF leak, proceed immediately to high-resolution CT (HRCT) of the skull base with thin-section bone algorithm and multiplanar reformation for leak localization. 1, 2
HRCT demonstrates 93% overall accuracy and 92% sensitivity for detecting skull-base defects, correctly identifying the leak site in 100% of surgical validation cases. 2
Alternative When Insufficient Fluid Available
If inadequate nasal fluid can be collected for β2-transferrin testing, DTPA radionuclide cisternography can confirm the presence of a CSF leak with 76-100% sensitivity and 100% specificity. 1
This imaging-based approach bypasses the need for fluid collection but provides lower spatial resolution for surgical planning. 1