What test should be conducted for unilateral clear rhinorrhea that worsens when leaning forward?

In cases where a patient presents with unilateral clear rhinorrhea that worsens when leaning forward, the clinical suspicion often points towards a possible cerebrospinal fluid (CSF) leak or a defect in the skull base. The β2-transferrin assay in nasal secretions is a highly specific test for the presence of CSF. β2-transferrin is a protein found in CSF but not in normal nasal secretions; therefore, its presence in nasal fluid strongly suggests a CSF leak. This makes it the most appropriate test in this scenario to confirm the suspicion of a CSF leak, particularly when considering the patient’s symptoms.

Nasal endoscopy could provide visual insights into the nasal passages but would not confirm the presence of CSF. A CT scan of the sinuses might be helpful for evaluating structural issues, but it won't specifically indicate a CSF leak. Allergy skin testing is not relevant in this situation, as it evaluates for allergic rhinitis rather than structural or fluid issues in the nasal cavity. Thus, the β2-transferrin assay is crucial for establishing a diagnosis related to unilateral rhinorrhea in the context described.