Why not choose your own System Organ Class?

August 31, 2016

For a long period of time I have used MedDRA and I have sometimes contemplated why as a coder we cannot choose our System Organ Classes in the same way that many companies choose to select WHO Drug ATC codes.  I have had calls from Medical Monitors requesting just that.  The answer according to the Maintenance and Support Services Organization (MSSO) makes logical sense.

According to the MSSO some of the applications for MedDRA include:

  • To aggregate reported terms in medically meaningful groupings for review, analysis and summary of safety data
  • To facilitate identification of standard data sets for evaluation of clinical and safety information
  • To facilitate consistent retrieval of specific cases or medical conditions from a database
  • To improve consistency in comparing and understanding safety signals and aggregated clinical data
  • To facilitate electronic data interchange of clinical safety information.

The International Council on Harmonization has authorized a group of drug safety experts to draft the “MedDRA Term Selection: Points to Consider” document as a guideline for MedDRA usage in coding adverse events, medical and social history, and indications.

This ICH-endorsed document states:

“MedDRA is a standardized terminology. It is considered essential that ad hoc structural changes in MedDRA not occur. The assignment of terms across SOCs is pre-determined within the terminology and should not be altered by users.”

We know that MedDRA is a multi-axial terminology meaning that a Preferred Term (PT) may be linked to more than one SOC. Each PT is assigned a primary SOC to avoid counting that term twice while retrieving information from all SOCs. In most instances, PTs relating to diseases or signs and symptoms are assigned to the prime manifestation site SOC. So, for PT Dyspnoea, the primary SOC is SOC Respiratory, thoracic and mediastinal disorders.

However, there are exceptions for three types of terms:

  • Terms for congenital and hereditary anomalies are assigned to SOC Congenital, familial and genetic disorders as the primary SOC
  • Terms for benign and malignant neoplasms are assigned to SOC Neoplasms benign, malignant and unspecified (incl cysts and polyps) as primary SOC. This does not apply to cyst and polyp terms. These terms have as their primary SOC assignment their site of manifestation SOC
  • Terms for infections are assigned to SOC Infections and infestations as the primary SOC

As is turns out any MedDRA basic or core subscriber may submit a proposal to change the primary SOC assignment for any given term through the usual Change Request process. In considering a customer’s request, the MSSO will carefully review the justification provided along with the already established allocation rules.

The logic involved in creating a primary path is consistent with the aim of MedDRA coding which is to capture the most information available when coding.  Unlike WHO Drug coding where a single concept can mean something different depending upon dosage, indication, location, language, and culture. MedDRA and the coding of medical terms tend to have the same meaning across the great cultural divide.

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