Test-retest reliability of the ulnar F-wave minimum latency in normal adults.

BACKGROUND AND PURPOSE: The purpose of this study was to measure the test-retest reliability of the ulnar F-wave minimum latency (Fmin) in normal adults. A reliable Fmin measure allows clinicians to ascribe changes in latency to true changes in a subject and not merely random daily variation. SUBJECTS AND METHODS: Fmin in the Abductor Digiti Minimi muscle was measured bilaterally in 49 healthy adults (n = 98) with a three day separation between tests. RESULTS: The Fmin reliability estimate as measured by intraclass correlation coefficient (3,1) was 0.59 with a standard error of measurement (SEM) of 1.3 msec. A paired t-test showed no significant difference (t = 1.7, df = 97, p > 0.05) between the mean scores from the two testing sessions. DISCUSSION AND CONCLUSIONS: We found moderate reliability and relatively low precision (high SEM) in Fmin scores taken from healthy individuals on two separate days. Strict adherence to our protocol and an acceptable overall precision of measurements (as measured by mean scores) suggest the contributions of rater and instrument error were low in our study. We conclude that 1) valid clinical interpretation of minimum F-wave latency findings is questionable because the Fmin measurement appears to have only moderate reliability, and 2) the lability of the phenomenon itself is the most likely contributor to variability in the Fmin latencies. Further research is warranted before electrophysiologists may be justified in attributing small changes in the Fmin to actual changes in the subject.