Beginning in 2008, Arizona supplied a third physician identifier. Arizona provides the National Provider Identifier (NPI).

In Arizona three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_R,
2. Operating physician is provided in MDNUM2_R, and
3. Other physician is provided in MDNUM3_R.

Beginning in 2016, Akansas provides the National Provider Identifier (NPI) for the type of physician identifier.

In Arkansas data, four types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_R
2. Operating physician is provided in MDNUM2_R
3. 1st other physician is provided in MDNUM3_R
4. 2nd other physician is provided in MDNUM4_R.

Physician identification numbers may not accurately track physicians within and across hospitals. Arkansas provides Universal Physician Identification Numbers (UPINs) and state license numbers. The provided physician identifiers are encrypted during HCUP processing. Beginning in 2008, Arkansas also provides National Provider Identifier.

In data year 2018, the source data provided by the HCUP Partner was missing a leading digit from some of the physician identification numbers. This will impact the reidentified value.

In District of Columbia, four types of physician identifiers are available:

1. Attending physician is provided in MDNUM1
2. Other physician in MDNUM2
3. Second other physician in MDNUM3, and
4. Third other physician in MDNUM4.

District of Columbia provides a combination of National Provider Identifier (NPI) and Universal Physician Identification Number (UPIN).

Beginning in 2010, Florida provides two identifiers for each physician. The new physician IDs are now housed in MDNUMn_R. Because of this change, MDNUMn_R cannot be used to link to data from previous years. The physican IDs that were housed in this field prior to 2010 are now kept in MDNUMOthern.

Three types of physician IDs are provided:

1. Attending Practitioner,
2. Operating or Performing Practitioner, and
3. Other Operating or Performing Practitioner.

In Georgia four types of physician identifiers are available beginning 2008:

1. Attending physician is provided in MDNUM1_R,
2. 1st other physician is provided in MDNUM2_R,
3. 2nd other physician is provided in MDNUM3_R, and
4. 3rd other physician is provided in MDNUM4_R.

Physician identification numbers may not accurately track physicians within and across hospitals. Prior to 2008, either the physician's state license number or the Universal Physician Identification Number (UPIN) were used to identify the physician. Beginning 2008, the national provider identification numbers (NPI) is provided. The provided physician identifiers are encrypted during HCUP processing.

In Iowa three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_R.
2. Physician that performed the principal procedure is provided in MDNUM2_R.
3. Referring physician is provided in MDNUM3_R (beginning 7/1/13).

Physician identification numbers may be used to track physicians within and across hospitals. Through 2006, Iowa reports Universal Physician Identification Numbers (UPINs). The provided physician identifiers are encrypted during HCUP processing.

For 2007, Admitting physician was not provided. Beginning in 2008, Iowa once again supplied a third physician identifier. Iowa reports the National Provide Identifier (NPI) or the Universal Physician Identification Numbers (UPIN).

Beginning in 2011, only the NPI is retained by Iowa in the physician fields. If a valid NPI is not available, a generic ID is used.

Beginning in 2017, Kentucky replaced the two consulting practitioner NPI numbers by the referring practitioner NPI (HCUP MDNUM3) and the patient's family practitioner NPI (HCUP MDNUM4).

Beginning in 2012, Kentucky supplies two additional consulting practitioner NPI numbers that are saved as HCUP data element MDNUM3 and MDNUM4.

Beginning October 2009, only NPIs accepted as valid IDs for both facilities and clinicians.

In Kentucky two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_R and
2. Physician that performed the primary procedure is provided in MDNUM2_R.

Physician identification numbers may not accurately track physicians within and across hospitals. Kentucky collects two different types of physician identifiers, National Provider Identifier (NPI) and state license numbers.

Mississippi provides three types of physician identifiers:

• Attending physician is provided in MDNUM1,
• Principal procedure ED physician is provided in MDNUM2, and
• Other physician is provided in MDNUM3

Physician identification numbers can be used to track physicians within and across hospitals. Mississippi provides the national provider identifier (NPI). During HCUP processing, the provided physician identifiers are encrypted.

Prior to 2015, Mississippi provided attending physician and operating physician numbers. These included National Provider Identification (NPI), UPIN, State License Number and Provider Commercial Number.

In Oregon, three types of physician identifiers are available; they added a fourth type and changed the label of their physician identifiers beginning in 2008:

1. Attending physician (beginning in 2008, attending clinician) is provided in MDNUM1_R,
2. 1st other physician (beginning in 2008, 1st other clinician) is provided in MDNUM2_R,
3. 2nd other physician (beginning in 2008, 2nd other clinician) is provided in MDNUM3_R, and
4. Operating room clinician is provided in MDNUM4_R.

Beginning in 2008, Oregon switched to NPI because it helps them identify the physicians better.

Physician identification numbers may not accurately track physicians across hospitals. Beginning in the 1997 data files, Oregon supplied the physician identifier number. Oregon encourages hospitals to use Universal Physician Identification Numbers (UPINs), but not all hospitals do. Information was not available from the data source about the prevalence of this practice. During HCUP processing, the physician identifiers were encrypted.

In South Dakota, three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_R
2. Physician who performed the principal procedure is provided in MDNUM2_R
3. Other physician is provided in MDNUM3_R.

Physician identification numbers can be used to track physicians within and across hospitals. Prior to 2007, South Dakota provides the Universal Physician Identification Numbers (UPINs).

In 2007, South Dakota did not provide MDNUM3_R.

Beginning in 2008, South Dakota once again provides a third physician identifier to HCUP. From 2008-2009, South Dakota provides the National Provider Identifier (NPI) or the Universal Physician Identification Number (UPIN).

Beginning in 2010, South Dakota provides only the National Provider Identifier (NPI). Because of a change in the way the source encrypts physician identifiers, physicians cannot be tracked from before 2010 to after 2010.

Beginning in 2014, the data source no longer provides a third physician identifier.

Washington changed their formats for physician numbers starting in 2009; they should all be NPIs.