OPS is an adaptation of the English-language International Classification of Procedures in Medicine (ICPM) by WHO. The German version of the ICPM resulted from the translation and expansion of the Dutch version ICPM-DE (Dutch Extension) and was further developed into OPS-301 and then OPS.

ICPM and ICHI of WHO

The need for an international classification of medical measures had been recognised as early as 1971. In 1978, WHO thus published its International Classification of Procedures in Medicine (ICPM). This was limited to surgical procedures. ICPM is part of the group of international health-related classifications. Because of the dynamics of medical-technical progress, the classification was costly to maintain and update; difficulties arose in international coordination. For that reason, work on the ICPM ceased in 1989. However, work on country-specific versions on a national level continued.

ICHI as the successor to the ICPM

In recent years, WHO has worked on a new classification of health interventions. The aim of this work is to create an internationally agreed classification that can be used for comparison and statistical exchange. For countries that do not yet have their own procedural classification, this new ICHI (International Classification of Health Interventions) is intended to be easily expandable. This new classification is also intended to cover traditional medicine and measures taken by public healthcare services.

OPS-301: Version 1.0 to Version 2.1

The German version of the ICPM resulted from the translation and expansion of the Dutch version ICPM-DE (Dutch Extension) and further developed into OPS-301. Of the 9 chapters of ICPM-DE, chapters 2,3,4,6 and 7 were omitted. OPS-301 version 1.0 was published in1994 by DIMDI on behalf of the Federal Ministry of Health (BMG) and used in inpatient care from 1995.

OPS-301 is a mainly numerical code with a monohierarchical structure, initially comprising 5 hierarchical levels. The four chapters in version 1.0 covered surgical prcedures (Ch. 5) as well as diagnostic (Ch. 1), non-surgical therapeutic (Ch. 8) and ancillary measures (Ch. 9).

The purpose of OPS-301 was greater transparency of services and costs. Its use to encode measures provided by hospitals was stipulated by the German Health Care Structure Act ("Gesundheitsstrukturgesetz GSG") and § 301 SGB V (Code of Soical Law Part V, "Sozialgesetzbuch Fünftes Buch"). OPS-301 permitted the billing of special reimbursement rates and case-based flat-rate payment of the old remuneration system as well as billing in accordance with the new G-DRG case-based fixed sum system, and it supported quality assurance documentation pursuant to § 137 SGB V.

In 2001, at the suggestion of the National Board for Classification in Health Care (KKG), the OPS Working Group (AG OPS) was set up at the DIMDI with representatives of all organisations involved with the KKG, in order to reach a consensus on the amendment required for OPS-301.

Version 2.0 was the first to include Chapter 3: Imaging Diagnostics

Versions 1.0, 1.1, 2.0 and 2.1 of OPS 301 were used from 1995 to 2003 exclusively for the encoding of surgical interventions in inpatient care.

Optional OPS

From version 2.1 (2003) to version 2008, in addition to the official catalogue of OPS-301, an extended catalogue existed to assist with the further development of the G-DRG system.ms.

Extended catalogue for OPS-301

In order to meet as many as possible of the requirements of procedural classifications, in 2002 DIMDI developed a concept for the future of OPS-301 that envisaged a two-track approach. OPS-301 was divided into an official core OPS and an optionally usable unofficial extended catalogue. The unofficial extended catalogue constituted an addition to the official OPS-301, with the idea of supporting the differentiation and optimization of the DRG catalogue, i.e. its primary rationale was the documentation of procedures likely to be required for calculation purposes. It was not intended as a tool for the traditional documentation of individual services and its use was to be voluntary. The first extended catalogue was made available in mid-2003.

In the print and online editions by DIMDI, codes from the unofficial extended catalogue are highlighted in grey. To ensure that users of the unofficial extended catalogue did not have to face additional encoding, entries in the EDP version of the unofficial catalogue included a designation of the code number in the official catalogue to be used for reimbursement purposes. From 2003 to 2008, both versions were published in parallel, the official version and the unofficial one including the extended catalogue.

With the 2009 version, the unofficial extended catalogue for OPS was discontinued; the optional codes were either transferred into the official catalogue or deleted.

The following notes apply to crosswalks between versions with or without extended catalogue:

"Überleitungen zwischen alten und neuen Versionen des OPS mit und ohne Erweiterungskatalog" (PDF, 36 kB) (Crosswalks between old and new versions of OPS with and without extended catalogue)

OPS: Version 2004 to current version

From version 2004, OPS-301 has been continued as OPS. As part of a structured annual proposal procedure, it is developed further by the self-administration partners represented in the OPS Working Group under the lead management of the DIMDI and published annually. The most significant content changes compared with the previous version are highlighted in a commentary in the preface to the respective Tabular List, the individual changes are listed in the list of changes.

2004 was the first publication of an Alphabetical Index to complement OPS. Since 2004, OPS has been used generally to encode medical procedures in inpatient hospital care.

Since 2005, OPS has also been used for outpatient surgical interventions.

In 2006, the chapter "Medikamente" (Drugs, medicaments and biological agents) was included; until then, medicines could only be considered from regularly updated chemotherapeutic lists.

In 2009, the optional OPS was discontinued and its codes either transferred to the official catalogue or deleted.

In 2010, OPS was first published in the WHO standard ClaML format.

In 2011, the ASCII book format was discontinued

Continuous development and improvement

OPS is further developed and improved through a structured and transparent proposal procedure and is currently revised on an annual basis.