Ethical approval for the research project was obtained from the Heath Research Authority National Research Ethics Service London – Queen Square Research Ethics Committee (Reference 17/LO/0750).
Neurophysiological data was collected based on the extensive and complete description of previous study designs by Padua  and Bland  and which is understood to be followed by most of the clinical laboratories in the United Kingdom. In addition, Second Lumbrical-Interosseous Latency was also recorded to distinguish between ‘very severe’ and ‘complete absent’ response grading of CTS .
The Association of Neurophysiological Scientists (ANS) (2014) guidelines and the minimum standards for the practice of Clinical Neurophysiology in the United Kingdom were followed. Few new grading was introduced during collection of the data to cover full range of grading.
The test was performed by a qualified Clinical Physiologist (Neurophysiology) using Keypoint 9033A07 (Skovlunde, Denmark) machine, on the bases of departmental protocol (Peripheral protocol1, 2015). A quantitative method was used for collecting data , to ensure accuracy and to avoid bias. The sample size of patients in the study was use for all those tested for NCS over a period of one calendar year (2017), across the population of North Wales. The data was collected from patients with an age range above 18 years, who were referred to the Neurophysiology department from the Orthopaedics and Neurology departments within the local Health Board, as well as General Practices (GPs) in North Wales. No individual patient was recruited in this research. The inclusion criteria were considered only on the basis of the referral diagnosis. No clinical assessment was conducted prior to the study in the department. Referral of CTS was considered based on paraesthesia, pain, swelling in median distribution area or digits I-V, worsened by sleep. The test was carried out by testing both hands (symptomatic and asymptomatic) to fulfil department protocol.
Data was analysed on certain widely accepted assumptions of sensory amplitude and CV and distal motor latency (DML), amplitude and CV [2, 6]. To introduce the terms “mild”, “moderate” and “severe”, a numerical value was used which could be accepted widely, and which can be used to compare with others studies .
The procedure started by carrying out the sensory testing, by placing the stimulating ring electrodes on digit III (which is more sensitive then digit II ) and the recording electrode on the surface of the median nerve on the wrist. The orthodromic technique was used for the sensory and motor NCS test, through the median and ulnar nerves. A maximal current was applied to record the full response of the nerve, at the digits II-IV for median sensory and digit V for ulnar sensory recording. A maximal current was applied to stimulate median nerve pathways at the wrist and at the elbow for motor recording from abductor pollicis brevis (APB)  and ulnar nerve pathways from First dorsal interosseous (FDI). Digit II was stimulated only when either the response from digit III was less than 3 μV or absent; digit IV was stimulated only when the response from digit III showed conduction velocity between 45 and 50 m/sec. Amplitude was recorded from peak to peak for sensory responses, and base to peak for motor responses. If responses were not recordable from median sensory digit II, III and motor from APB muscles, then motor responses were elicited by placing recording electrodes on 2nd lumbricals by stimulating median and ulnar nerves at the wrist [7, 10,11,12].
All patient data was collected by fulfilling the criteria mentioned in above paragraph depending on the severity. The reason for using the new criteria is to describe the full range of severity which was not fully covered by other research mentioned earlier in this paper. Criteria was mentioned in above paragraph are intended to be more reliable in terms of grading for Clinical Physiologist and probably will allow support to the Surgeon in terms of patient treatment decisions.
The grades are:
Normal (Grade 0): where sensory conduction velocity (SCV) is above 50 m/s and amplitude ≥5 μV with DML ≤4.2 ms, amplitude ≥5 mV and motor conduction velocity (MCV) ≥50 m/s.
Early (Grade 1): where SCV is between 45 and 50 m/s from digit III and double peak latency in digit IV is > 0.5 ms with DML ≤4.2 ms and normal sensory and motor amplitude > 5 (sensory in μV and motor in mV).
Mild Sensory (Grade 2): where SCV is between 40 and 44.9 m/s from digits III with normal sensory amplitude and motor values mentioned in Grade 0.
Mild Sensory-Motor (Grade 3): where SCV is between 40 and 44.9 m/s from digits III with normal sensory amplitude mentioned in Grade 0, DML ≥4.2 ms with normal motor amplitude and CV.
Moderate Sensory (Grade 4): where SCV is less than 40 m/s from digits III with normal sensory amplitude and normal motor values mentioned in Grade 0.
Moderate Sensory-Motor (Grade 5): where SCV is less than 40 m/s from digits III with normal sensory amplitude, DML ≥4.2 ms with normal motor amplitude and CV.
Severe Sensory-Motor (Grade 6): where sensory potentials from digits III and digit II are absent or < 3 μV in both digits III and II with SCV < 30 m/s, DML ≥4.2 ms, MCV is either slow or normal.
Extremely Severe Sensory-Motor (Grade 7): where sensory and motor potentials are absent and response recordable only from 2nd lumbricals, where median lumbricals are prolonged compared and low amplitude to ulnar lumbricals.
Complete (Grade 8): where both sensory and motor potentials are absent and responses are not recordable from median 2nd lumbricals but recordable from ulnar 2nd lumbricals. (Please refer to a Comparison of the Bland  grading with the proposed revised grading is given at the end of this study for more understanding).