Skip to Main Content

OASIS User Manuals

OASIS-C Information

Changes to Implementation of OASIS-C1 Caused By the Legislatively Mandated One Year ICD-10 Delay

The original version of the OASIS-C1 data item set was approved by The Office of Management & Budget (OMB) on February 6, 2014.  OASIS-C1 was scheduled for implementation on October 1, 2014, to coincide with the implementation of ICD-10. However, on April 1, 2014, the Protecting Access to Medicare Act of 2014 (PAMA) (Pub. L. No. 113-93) was enacted.  This law prohibits CMS from implementing ICD-10 prior to October 1, 2015.

The original version of OASIS-C1 contains five (5) items that require ICD-10 codes.  Since CMS cannot implement ICD-10 prior to October 1, 2015, it was necessary to create an interim version of OASIS-C1 that can be used during the ICD-10 delay.  This interim version of OASIS, titled OASIS-C1/ ICD-9 Version, uses ICD-9 coding and can be used until ICD-10 is implemented.  

Guidelines for Use of the Different Versions of the OASIS Data Item Set

Below are some guidelines that will help Home Health Agencies (HHAs) understand the differences between the versions of OASIS and what time periods each OASIS version must be used.  A description of changes in the OASIS submission process is also provided below.


  • OASIS-C was implemented on 01/01/2010;
  • OASIS-C is currently in use by Home Health Agencies;
  • OASIS C use will continue until 11:59 p.m. (E.T.) on December 31, 2014.            (The use of OASIS-C was extended for a three month period due to the legislatively mandated ICD-10 delay)

OASIS-C1/ ICD-9 Version

  • OASIS-C1/ ICD-9 Version is an interim version of OASIS that was created for use during the legislatively mandated ICD-10 delay;
  • To create the OASIS-C1/ ICD-9 Version, the following five items which use ICD-10 codes have been removed from the OASIS-C1 data item set: (M1011, M1017, M1021, M1023, M1025); and
  • The five ICD-10 based items have been replaced with corresponding ICD-9 based items from the OASIS-C data item set (M1010, M1016, M1020, M1022, and M1024);
  • The replacement items retain their OASIS-C based numbering in the OASIS-C1/ ICD-9 Version data item set.
  • OASIS-C1/ ICD-9 Version will go into effect on January 1, 2015 at 12:00 a.m. (E.T.);
  • OASIS-C1/ ICD-9 Version will remain in effect until one of the following events occur (whichever occurs first):
    • September 30, 2015 at 11:59 p.m.;
    • ICD-10 is implemented; or
    • Another decision is made by CMS.


OASIS-C1 will go into effect upon the occurrence of one of the following events, (whichever occurs first):

  • 12:00 a.m. (E.T.) on October 1, 2015; or
  • 12:00 a.m. (E.T.) on the first day that ICD-10 goes live

Changes to the Submission Process for OASIS-C1

  • Effective January 1, 2015, all OASIS assessment data will be submitted to CMS via the national OASIS Assessment Submission and Processing (ASAP) system.  
  • With the implementation of the OASIS ASAP system, Home Health Agencies will no longer submit OASIS assessment data to CMS via their state databases.
  • In order to transition the OASIS data submission process from the state databases to the ASAP system:
    • The state based OASIS data submission system will shut down permanently at 6:00 p.m. (ET) on December 26, 2014;
    • The OASIS ASAP system will become available at 12:00 a.m. (ET) on January 1, 2015. 
    • During the time period of December 26, 2014 at 6:00 p.m. (ET) through December 31, 2014 at 11:59 p.m. (ET), no OASIS assessment data will be accepted.  However, OASIS assessment data collected during this time period, may be submitted on or after January 1, 2015 using the ASAP system.
  • Any OASIS assessments submitted on or after January 1, 2015, must be submitted using the ASAP system;
    • OASIS-C data must be submitted using version 2.10 of the OASIS data submission specifications, which supports OASIS-C data submission; and
    • OASIS-C1 data must be submitted using version 2.11 of the OASIS data submission specifications, which supports OASIS-C1 data submission.

OASIS-C1/ ICD-9 Version Guidance Manual

The final guidance manual for the OASIS-C1/ ICD-9 Version data item set, effective January 1, 2015, is now available in the Downloads section below.