E-Norms

A Method to Extrapolate Reference Values From a Laboratory Population

Abstract

Purpose: 

Collecting reference values in subpopulations such as infants and children can pose a daunting challenge to gather through epidemiologic studies. The authors propose to evaluate a method the authors refer to as extrapolated norms (e-norms) to derive Stimulated Single Fiber EMG jitter reference values from the laboratory data of pediatric and adult cohorts. Single Fiber EMG studies are considered the gold standard test for evaluation of neuromuscular transmission disorders.

Methods: 

Data that lie in the plateau part of an inverted S curve derived from sorted jitter data were used to calculate descriptive statistics for pediatric and adult e-norms jitter.

Results: 

The e-norms derived jitter was 22 ± 2.83 μs for our pediatric and 21 ± 2.79 μs for our adult cohort. Our adult e-norms values compared favorably with the 22 ± 1.99 μs published jitter range derived from a healthy adult cohort.

Conclusions: 

The e-norms method the authors describe seems to be useful in recovering reference ranges when such values are difficult to obtain, such as in a pediatric subpopulation.