In data year 2019, Colorado started transitioning to using NPI but many hospitals had not yet transitioned. Around 65% of MDNUMn values were set to missing because hospitals used the generic NPI of '1234567890.' Also, because of this change, MDNUMn_R cannot be used to link to data prior to 2019.

Prior to data year 2019, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1 and
2. Physician that performed the principal procedure is provided in MDNUM2.

Physician identification numbers may not accurately track physicians across hospitals. The state encourages hospitals to use the Professional State License Number as an identifier, but some hospitals continue to use their own internal identification number. Also, some hospitals appear to pad the Professional State License Number (a 5-digit code). Information was not available from the data source about the prevalence of these practices.

Some hospitals may use one license number for all physicians in order to protect physician confidentiality.

Beginning in 2004, Colorado encrypted physician identifiers prior to submission to HCUP. Prior to 2004, physician identifiers were not encrypted by Colorado but were encrypted by HCUP during processing.

Beginning in 2012, Colorado changed the encryption of their physician identifiers. Because of this change, MDNUMn cannot be used to link to data from previous years.

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.

Three types of physician IDs are provided:

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

In 2006, Florida changed the format of their physician identifiers. The identifiers cannot be used to link to data from previous years.

Beginning in 2005, Florida changed the format of their physician identifiers. The identifiers cannot be used to link to data from previous years

Also, Florida provided three types of physician IDs:

1. Attending Physician ID Number in MDNUM1_R,
2. Operating or Performing Physician ID Number in MDNUM2_R and
3. Other Physician ID Number in MDNUM3_R (new in 2005).

Prior to 2005, Florida provided two types of physician identifiers (re-identified):

1. Attending physician is provided in MDNUM1_R and
2. Operating physician is provided in MDNUM2_R.

Physician identification numbers may be used to track physicians within and across hospitals. Florida reports state license numbers for the physician identifiers. During HCUP processing, physician identifiers were encrypted.

Caution should be used when tracking physicians across 2003. The physician identifiers supplied by the data source do not conform to the documented pattern. Not all identifiers included a two-character prefix, and not all hade the same length.

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. Prior to 2007, Iowa reports Universal Physician Identification Numbers (UPINs). The provided physician identifiers are encrypted during HCUP processing.

Beginning in 2007, 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.

Beginning 2018 Q3, Maryland provides two physician identifiers:

1. Attending physician NPI is provided in MDNUM1
2. Operating physician NPI is provided in MDNUM2 (previously provided in MDNUM1 from 2009-2018 Q2)

From 2009 through 2018 Q2, MDNUM1 includes operating physician NPI. Physician identification numbers can be used to track physicians within and across hospitals.

Prior to 2009, Maryland reported a state license operating physician number assigned by MedChi, The Maryland State Medical Society. This was included in MDNUMOTHER1 from 2009 through 2018 Q2 and included in MDNUMOTHER2 beginning 2018 Q3 (state license attending physician number is provided in MDNUMOTHER1 beginning 2018 Q3). The provided physician identifiers are encrypted during HCUP processing.

Beginning in 2007, Maryland included the records from all other outpatients, Greenbaum cancer center, and UMMS shock trauma in the unified AS and ED outpatient data file. The inclusion of these new records resulted in a large increase in the frequency of MDNUM1.

From 2003 - 2005 physician identifiers were encrypted by the state of Maryland prior to submission to HCUP.

Beginning in 2012, Michigan provides the National Provider Identifier (NPI).

Beginning in 2007, a few Michigan hospitals changed the format of their physician identifiers. This change will render their physician identifiers incomparable to previous years.

In Michigan, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_R and
2. Primary surgeon is provided in MDNUM2_R.

Physician identification numbers do not accurately track physicians across hospitals. Michigan reports hospital-specific physician identifiers. During HCUP processing, physician identifiers were encrypted.

In Missouri, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_R and
2. Primary surgeon is provided in MDNUM2_R.

Physician identification number may not accurately track physicians within and across hospitals. Missouri accepts National Provider Identifiers (NPIs), Universal Physician Identification Numbers (UPINs), state license numbers, and hospital-assigned physician identification numbers. According to the source, the majority of physician identifiers are UPINs.

Beginning in 2017, four types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_R,
2. Operating physician is provided in MDNUM2_R,
3. Other operating physician is provided in MDNUM3_R,
4. Rendering physician is provided in MDNUM4_R

Physician identification numbers may not accurately track physicians within and across hospitals. During HCUP processing, physician identifiers are encrypted. The coding of the physician identification number varies across years:

Beginning in 2008, attending physician state license numbers are contained in MDNUMOTHER1.

Beginning October 1, 2017, New York changed from State Licence Numbers to NPI and changed from eight-character length to ten-character length. Physician identifiers are missing on discharges when there is any indication of abortion as identified by New York.

For 2001 - 2016 New York identifies an indication of induced abortion by ICD-9-CM diagnosis code (admitting, principal, or secondary) of "6350" through "6399", or "7796" or procedure code (principal or secondary) of "690", "695", "696", "6993", "738", "7491", "750", "751" (prior to 2005) or "9649". Please note that the admitting diagnosis is not retained in the HCUP databases prior to 2012.

In New York, 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.

Physician identification numbers can be used to track physicians within and across hospitals. New York reports state license numbers as physician identifiers. Source documentation indicates that if the reported physician number did not possess a valid New York state license number, the license number of the Chief of Service should have been reported.

New York does not limit this field to physicians; dentists, podiatrists, psychologists, nurse/midwives, and other licensed health care professionals or facilities may be included.

The provided physician identifiers are encrypted during HCUP processing.

In Oregon, four types of physician identifiers are available:

1. Attending Clinician is provided in MDNUM1_R,
2. Operating room Clinician is provided in MDNUM2_R,
3. 1st Other Clinician is provided in MDNUM3_R, and
4. 2nd Other Clinician is provided in MDNUM4_R.

Prior to 2013, two 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.

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

From 2007-2009, 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 2013, three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_R
2. Operating physician is provided in MDNUM2_R
3. Referring physician is provided in MDNUM3_R