Revising nerve conduction reference limits

Our electrodiagnostic laboratory uses reference limits (RL) that have been handed down for four decades. With changes in instrumentation and technique, we wish to know if our RL should be modified. It is also useful to have RL based on patient demographics.

Latency and velocity data from motor nerve conduction studies of 740 adult patients studied over an 8 mo period were tabulated. RL were derived using both extrapolated reference value (ERef) and multi-variable extrapolated reference value (MeRef) methods.

Distal latency values showed a significant but weak correlation with age and/or height. ERef limits for the median and ulnar nerve latency (3.96 and 3.45 ms, respectively) were very similar to current laboratory limits (3.9 and 3.3 ms, respectively). ERef limits for the tibial and fibular nerve latency (5.1 and 4.95 ms, respectively) were slightly shorter. Ulnar velocity did not depend on age or height. The ERef limit was the same as our present laboratory limit (50 m/s). Median and tibial velocity limits decreased with age (R²  > 0.25). Fibular motor nerve conduction limits decreased with age and height (R²  = 0.39).

ERef and MeRef were useful to validate and revise our latency and velocity RL. We will use ERef limits for tibial and fibular latency. MeRef generated linear regression equations based on age and/or height will be used for conduction velocity analysis of median, fibular, and tibial nerves. This will increase the specificity of our values.