Mapping between ICD-10 and ICD-9

At the National Data Policy Group (NDPG) meeting on 7 February 2000, members agreed that New Zealand would move to include the third mapping fix in our ICD-10-AM to ICD-9-CM-A mapping from 1 July 2000.

This principally accommodates the current inconsistencies in mapping diverticular disease with complications. This fix only affects backwards (ICD-10-AM to ICD-9-CM-A) mapping, but the forward mapping file (ICD-9-CM-A to ICD-10-AM) is included here also for completeness.

The following files are available:

The previous mapping files and the accompanying documentation are given below.

ICD-10 mapping documentation

Note that as of 1 July 2000 these files have been superseded by new files which incorporate the 3rd mapping fix – see above.

Note: The Ministry of Health would like to acknowledge the support and assistance given by the Department of Human Services, Victoria, in the development of these mapping files.

The software to map between ICD-9-CM-A and ICD-10-AM comprises three mapping files, each in Excel spreadsheet format:

These files are logical maps and they all include the first and second Victorian coding fixes.

Logical maps ensure that for a given ICD-10-AM code, the backward ICD-9-CM code and any ICD-9-CM codes which forward map to the code are in the same principal diagnosis list for the grouper.

Ministry of Health validation process

The Ministry of Health has reviewed the NCCH mappings and the Victorian fixes, and where we have queries we have forwarded them to Victorian Department of Human Services. This is the same process as followed by Victorian hospitals. Victoria reviews these queries and where they result in changes to the mapping tables, all hospitals and encoder developers, along with the Commonwealth Office, who define the grouper specifications, are advised. This process ensures those New Zealand hospitals, the Ministry of Health and 3M are all using the same mappings, which are up to date, and also that data from New Zealand hospitals is consistent with that in Victoria.

In order to validate our understanding and application of the mapping files, the Ministry of Health has programmed them in two languages (SAS and Java). We have processed a year of NMDS data through these mappings and compared the results to ensure that they are identical. As a further check, Victoria supplied the Ministry of Health with a file of 257,000 records of their ICD-10 data. We mapped this back to ICD-9 and validated our DRGs against the Victorian file.

The Ministry of Health can assist hospitals that are programming the mappings into their local systems, by providing a copy of the code we have written, and also files of test data to validate their results.

One-to-one mapping

All of the forward mappings are in a one-to-one format. Most of the backward mappings are also one-to-one, although where either the ICD-10 or the ICD-9 codes capture more complexity the mappings are in a format of one-to-many. The largest number of codes involved is one ICD-10 code which maps to three ICD-9 codes. There are also cases where two ICD-10 codes map to one ICD-9 code.

Complex mapping

The complex mapping must be applied before to the calculation of the AN-DRG.

Obstetric

Problem

The obstetric V3.1 DRGs are based on the fifth digit of the ICD-9-CM code which indicates the type of episode: delivery, antepartum or postpartum. The ICD-10-AM codes do not capture this information. The mapped ICD-9-CM code includes the most common fifth digit. However, a range of fifth digits is applicable.

Solution

Delivery episodes will contain Z37.x in the code string. Post partum episodes will contain Z39.0x in the code string. Antepartum episodes will have neither of these.

  1. Flag obstetric codes O10.0 - O99.8 (except O80).
  2. Search code string for presence of Z37.x. If present, assign mapped code from column 3 of the table (5th digit of 1 or 2). Repeat for every (flagged) obstetric code in the string. If Z37.x not present, then
  3. search code string for presence of Z39.0x. If present, assign mapped code from column 4 of the table (5th digit of 4 or 0). Repeat for every (flagged) obstetric code in the string. If Z39.0x not present, then
  4. Assign mapped code from column 5 of the table. Repeat for every (flagged) obstetric code in the string.
  5. Else, map as per library file (including Z37.x and Z39.0x).

See the Obstetric table in the complex mapping file (Excel, 87 KB).

Head injury

Problem

ICD-9-CM head injury codes have fifth digits indicating duration of loss of consciousness (LOC). V3.1 DRGs 50-52 are based on these fifth digits. The fifth digit does not exist in ICD-10-AM where the LOC is captured by separate code. The mapping of head injury code defaults to a fifth digit of 0. The effect is to shift severe head injuries from DRG 50 to DRG 51.

Solution

For head injury –

  1. Flag relevant head injury codes as per table.
  2. This complex mapping will be activated regardless of the position of the head injury code, ie it may be principal diagnosis or secondary diagnosis.
  3. Search code string for presence of S06.0x (see the table for specific 5th characters). S06.0x may be in any position.
  4. If S06.0x is present, from the combination of the two ICD-10-AM codes, assign the appropriate mapped code from the table. Repeat for every (flagged) head injury code in the string.
  5. Else, map codes as per library file (including S06.0x).

See the Head Injury table in the complex mapping file (Excel, 87 KB).

Tendon injury

Problem

In ICD-9-CM tendon injuries are classified in two ways: open wound with tendon involvement (880-890) and strains/sprains (840). ICD-10-AM classifies all types of tendon injury by a single code. Open wound, if present, is indicated by a second code. The one-to-one maps for tendon injury codes are the strain/sprains. The effect is to shift the open-wound tendon injuries to sprain/strain DRGs.

Solution

Flag relevant tendon injury codes and open wound codes as per table.

  1. Search for tendon injury code as principal diagnosis. If present,
  2. and the second code forms a valid combination in the table, assign the appropriate mapped code from the table.
  3. Else, map as per library file (including the second code).

(Note: second code means second listed code, not secondary code.)

See the Tendon table in the complex mapping file (Excel, 87 KB).

Social induction

Problem

Social induction is coded to O80 Normal delivery, as there is no equivalent of the ICD-9-CM code 659.8x. ACS 1505 (July 98) allows a defined range of procedure codes to be used with O80. However, O80 maps to 650 which allows a smaller range of procedure codes, excluding induction codes. The combination of O80 and induction procedure codes groups to DRG 951 Unacceptable obstetric Pdx.

Solution

For social induction –

  1. Flag O80.
    If O80 is principal diagnosis and procedure codes include one of the following, {block [1334]: 90465-00, 90465-01, 90465-02, 90465-03, 90465-04, 90465-05}, map principal diagnosis to code 659.81. If none of these procedure codes are present map, O80 to 650 as per library file.
  2. Map all other codes in the string, including procedure codes, as per library file.

Medical augmentation with normal delivery

Problem

In ICD-9-CM medical augmentation was not coded. Medical augmentation code 90466-00 [1335] is mapping to 73.49 Other and unspecified medical induction. ACS 1505 permits a combination of O80 and 90466-00 but this will map to 650 + 73.49 and group to DRG 951. (Social induction complex fix will not be activated as it is based on the MBS-E codes not ICD-9-CM, and 90466-00 is not included.)

Solution

Where O80 is the principal diagnosis and 90466-00 is a procedure code, map 90466-00 to a blank. Any subsequent procedure codes must be moved up to fill the blank.

Replacement of pacemaker or components

Problem

ICD-9-CM had codes for insertion, replacement and removal of pacemakers and components. ICD-10-AM does not have replacement codes, so a replacement is coded with a combination of insertion and removal codes. The ICD-9-CM replacement codes are the only codes to take cases into DRGs 294/295. The one-to-one mappings do not achieve these codes, thus taking replacement cases into DRG 296.

Solution

  1. Flag ICD-10-AM pacemaker and pacemaker component insertion and removal codes as per table.
  2. If the insertion code is immediately followed by a removal code (valid combination as per table), map the two codes to the single mapped code as per the table.
  3. Else, map as per library file (including the removal code).

See the Pacemaker table in the complex mapping file (Excel, 87 KB).

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