F wave to height or limb length ratios as rational alternatives for F wave latency in clinical electrodiagnostic medicine.

Objective: To delineate the F wave latency/height (F min/He) or F wave latency/limb length (F min/L) ratio as a more useful alternative for the currently reported shortest latency in milliseconds.

Methods: One hundred and sixty-six healthy volunteers, 85 upper limbs and 84 lower limbs entered the study. Minimum F wave latencies were determined in median, ulnar, tibial and peroneal nerves. The F min/He and F min/L ratios of each nerve were calculated.

Results: F latencies of all nerves had significant correlation with height and limb length but there was no correlation between either F min/He or F min/L and height in any nerve except for peroneal F min/He (p = 0.04, r = 0.23).

Conclusions: Using the F min/He or F min/L ratios are more accurate than reporting only the F wave minimum latency, since these ratios incorporate corrections for height and/or limb length. This method also eliminates the false positive and negative reports caused by using a single reference table for all heights.

Significance: A unique reference table can be produced using the F min/He or F min/L for all populations and races, so that the comparison between different population samples can be done easily. Also data of different investigations can be pooled together for meta-analysis purposes when a single reference table is used for different samples.