What is the initial step in calculating the check digit of a DEA number?

The initial step in calculating the check digit of a DEA number indeed involves adding the digits in odd positions, specifically the first, third, and fifth digits of the number. This is paramount in the overall process of determining the validity of a DEA number. The DEA number is composed of two letters followed by seven digits, and the structure is designed such that the check digit is derived systematically to prevent errors or fraud.

Adding these odd-position digits provides a foundational part of the calculation as the final check digit will depend on a weighted sum that incorporates both odd and even positions' values. This step is critical as it sets the groundwork for the subsequent operations needed to determine the check digit, which ultimately aids in verifying whether a DEA number is legitimate.

Understanding this initial step is crucial because it highlights the organization and methodology behind the DEA number system, ensuring pharmacy professionals can accurately verify prescription authority.