PURPOSE: To clarify the sensitivity, specificity, and interrater reliability of 
the scratch collapse test for carpal tunnel syndrome (CTS) and cubital tunnel 
syndrome, using blinded observers in a general patient population.
METHODS: Ninety-two subjects were recruited from all patients referred for 
electrodiagnostic studies for upper extremity symptoms that were thought to be 
related to an entrapment mononeuropathy. The scratch collapse test was performed 
twice on each patient, once by the resident and once by a nerve conduction 
technician. Both observers were blinded to all aspects of the patient's 
presentation. Sensitivity and specificity for the scratch collapse test were 
calculated twice, once using electrodiagnostic testing results and a second time 
using a validated clinical tool (the CTS-6) as the reference standard. The 
interrater reliability was also calculated.
RESULTS: Using electrodiagnostic criteria as a reference standard, the scratch 
collapse test had a sensitivity of 7% and a specificity of 78% for CTS. Using 
clinical criteria as a reference standard, the test had a sensitivity of 15% and 
a specificity of 87%. For cubital tunnel syndrome, the sensitivity was 10% and 
the specificity was 90%. For the resident/technician 1, kappa was -0.025 (worse 
than chance alone). For the resident/technician 2, kappa was 0.211 (fair 
strength of agreement).
CONCLUSIONS: The sensitivity of the scratch collapse test for CTS and cubital 
tunnel syndrome was lower than that found in other studies, regardless of 
whether a clinical or an electrodiagnostic reference standard was used. The 
specificity was high. Overall interrater agreement was lower than previously 
reported. These results call into question the sensitivity and interrater 
reliability of the scratch collapse test for CTS and cubital tunnel syndrome.
TYPE OF STUDY/LEVEL OF EVIDENCE: Diagnostic II.