HCUP encrypted physician identifiers are referred to by different names in the HCUP data across years.

MDNUM1_S contains a fixed-key (one-to-one) encryption of the supplied physician 1 number (MDNUM1), according to the following rules:

• All alphanumeric digits are used in the encryption.
• All symbols such as ".,:;'*@" are retained in the encrypted value, but not in the same location.
• Leading zeros are encrypted so that the two original physician identifiers "000A6" and "A6" are distinctly different.
• When the original physician 1 number and physician 2 number identifiers are the same, the synthetic identifiers, MDNUM1_S and MDNUM2_S, are the same.
• When the MDNUM1 in the ambulatory surgery data and the inpatient data are the same, the synthetic identifier, MDNUM1_S is the same.

Except in those data sources where physician license numbers are supplied, it is not known whether the physician identifier MDNUM1_S refers to individual physicians or to groups. If the physician 1 numbers supplied by the data source are not restricted to license numbers, the state-specific note includes available information about reporting practices, including whether MDNUM1_S refers to individual physicians or to groups.

Beginning in the 1993 data, supplied physician 1 identifiers were checked for null characters. If null characters were found, they were replaced by blanks before the identifier was encrypted. Since this conversion was not done in prior years of HCUP data, the encrypted physician 1 identifiers from 1993 on may not match those in earlier years. However, null characters are rarely included.

Beginning with the 1993 NIS, supplied physician 1 identifiers were checked for null characters. If null characters were found, they were replaced by blanks before the identifier was encrypted. Since this conversion was not done in prior years of HCUP inpatient data, the encrypted physician 1 identifiers from 1993 on may not match those in earlier years. However, no null characters were found in the 1994 identifiers, and they were rare in prior years.

In Arizona two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S and
2. Physician that performed the primary procedure is provided in MDNUM2_S.

Physician identification numbers may not accurately track physicians across hospitals for the following reasons:

• Some hospitals assign their own internal physician identification numbers rather than using the license numbers issued by the licensing agency of the physician or other health care practitioner. Information was not available about the prevalence of this practice.
• Some hospitals use one physician identification number for several physicians that are part of the same physician practice group. Information was not available about the prevalence of this practice.
• Physician identifiers in July-December 2002 generally include a first-digit prefix of "1"; in other periods, the prefix is generally "0".

The physician identification number includes license numbers from the following board of examiners: Medical, Osteopathic, Podiatrists, and Nurses. In addition, Arizona accepts licensing numbers from other health practitioner licensing boards, but these boards are unspecified. The provided physician identifiers are encrypted during HCUP processing.

The physician identifiers provided by Arizona for the second half of 2002 were constructed differently than the first half of 2002 and following years (i.e., 2003 forward). Physicians cannot be accurately tracked across the second half of 2002.

In Colorado two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S and
2. Physician that performed the principal procedure is provided in MDNUM2_S.

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. Information was not available from the data source about the prevalence of this practice. The provided physician identifiers are encrypted during HCUP processing.

In Florida two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S and
2. Operating physician is provided in MDNUM2_S.

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.

In Georgia three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S,
2. 1st other physician is provided in MDNUM2_S and
3. 2nd other physician is provided in MDNUM3_S.

Physician identification numbers may not accurately track physicians within and across hospitals. Either the physician's state license number or the Universal Physician Identification Number (UPIN) is used to identify the physician. 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_S.
2. Physician that performed the principal procedure is provided in MDNUM2_S.
3. Admitting physician is provided in MDNUM3_S.

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

In Kansas two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S and
2. Primary surgeon is provided in MDNUM2_S.

Physician identification numbers may be used to track physicians within and across hospitals. Kansas reports Universal Physician Identification Numbers (UPINs) and state license numbers for the physician identifiers.

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_S and
2. Physician that performed the primary procedure is provided in MDNUM2_S.

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.

In Maine, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S.
2. Operating surgeon is provided in MDNUM2_S.

Maine provides state-specific encrypted physician identifier numbers that allow for tracking physicians within and across hospitals. The provided physician identifiers are encrypted again during HCUP processing.

Caution should be used when tracking physicians back to 1999 inpatient data. The encrypted values supplied by the data source in the 1999 inpatient data contained slightly different coding than the values supplied beginning in the 2000 inpatient and ambulatory surgery data.

In Maryland, two types of physician identifiers are available:

1. Attending physician NPI is provided in MDNUM1_S and
2. Operating physician NPI is provided in MDNUM2_S.

Physician identification numbers can be used to track physicians within and across hospitals.

Prior to 2009, MDNUM1 and MDNUM2 contained state license numbers assigned by the Maryland State Medical Society (MedChi). Source documentation describes strict assignment and verification rules for this field.

State license numbers are available in MDNUMOTHER1-2 starting in 2009

From 2003-2005, physician identifiers were encrypted by the state of Maryland. Beginning in 2006, the encryption occurs during HCUP data processing.

Prior to 2003, the supplied physician identifiers were unencrypted.

In Michigan, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S and
2. Primary surgeon is provided in MDNUM2_S.

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

In Minnesota, three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S,
2. Other physician in MDNUM2_S, and
3. Second other physician in MDNUM3_S.

The physician identifiers may not accurately track physicians within and across hospitals. Minnesota provides a combination of Universal Physician Identification Number (UPIN), state license numbers, and hospital-specific numbers. During HCUP processing, this number is encrypted.

In Missouri, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S and
2. Primary surgeon is provided in MDNUM2_S.

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.

In Nebraska, two physician identifiers are available:

1. Primary physician is provided in MDNUM1_S and
2. Secondary physician in MDNUM2_S.

Physician identification numbers may not accurately track physicians across hospitals. The state encourages hospitals to code Universal Physician Numbers (UPINs) as an identifier, but some hospitals continue to use the Professional State License Number.

In Nevada, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S, and
2. Operating physician is provided in MDNUM2_S.

Physician identification numbers can be used to track physicians within and across hospitals. Nevada provides the physician's state license number. During HCUP processing, this number is encrypted.

Prior to 2003, Nevada supplied a 6-digit physician state license number. These identification numbers contain a 2-digit specialty code that hospitals place in front of the 4-digit license number. Beginning with 2003, Nevada elected to request license numbers without the specialty codes. Nevada supplies the 4-digit state license number in a 6-digit field. Some 5- and 6-digit codes may occur in the data subsequent to the change in specifications.

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

1. Attending physician is provided in MDNUM1_S,
2. Operating physician is provided in MDNUM2_S,
3. Other operating physician is provided in MDNUM3_S,
4. Rendering physician is provided in MDNUM4_S

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:

In New York, three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S,
2. Operating physician is provided in MDNUM2_S, and
3. Other physician is provided in MDNUM3_S.

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 may be included. It is impossible to identify the different types of providers in the HCUP data.

The provided physician identifiers are encrypted during HCUP processing.

For the 2001 - 2002 data, physician identifiers are missing (" ") on discharges with an indication of an induced abortion. New York identifies an indication of induced abortion by ICD-9-CM diagnosis or procedure code:

• An admitting, principal, or secondary diagnosis of "6350" through "6399", or "7796".
• A principal or secondary procedure of "690", "695", "696", "6993", "738", "7491", "750", "751", or "9649".

Please note that the admitting diagnosis is not retained in the HCUP databases.

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

1. Attending physician is provided in MDNUM1_S,
2. Other physician in MDNUM2_S, and
3. Second other physician in MDNUM3_S.

The physician identifiers may not accurately track physicians within and across hospitals. North Dakota provides a combination of Universal Physician Identification Number (UPIN), state license numbers, and hospital-specific numbers. During HCUP processing, this number is encrypted.

In Oregon, three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S,
2. 1st other physician is provided in MDNUM2_S, and
3. 2nd other physician is provided in MDNUM3_S.

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 Pennsylvania, three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S,
2. Operating physician is provided in MDNUM2_S, and
3. Referring physician is provided in MDNUM3_S.

Physician identification numbers can be used to track physicians within and across hospitals. Pennsylvania reports the state license numbers. The provided physician identifiers are encrypted during HCUP processing.

In Rhode Island, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S,
2. Principal surgeon is provided in MDNUM2_S.

Physician identification numbers may not accurately track physicians across hospitals. Rhode Island provides blinded, hospital-specific numbers that cannot be linked to individual physicians. During HCUP processing, the provided physician identifiers are encrypted.

In South Carolina, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S and
2. Other physician is provided in MDNUM2_S.

Physician identification numbers can be used to track physicians within and across hospitals. South Carolina reports six-character state license numbers. When the source values were shorter than six characters, the HCUP value was padded to bring it into conformity with South Carolina's format before the value was encrypted.

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

1. Attending physician is provided in MDNUM1_S
2. Physician who performed the principal procedure is provided in MDNUM2_S
3. Other physician is provided in MDNUM3_S.

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

In Tennessee, three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S,
2. 1st other physician is provided in MDNUM2_S, and
3. 2nd other physician is provided in MDNUM3_S.

Physician identification number may not accurately track physicians within and across hospitals. Tennessee collects two different types of physician identifiers from hospitals: Universal Physician Identification Numbers (UPINs) and state license numbers. The provided physician identifiers are encrypted during HCUP processing.

In Texas, three types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S,
2. Operating physician is provided in MDNUM2_S, and
3. Other physician is provided in MDNUM3_S (not available beginning in 2001).

Physician identification numbers can be used to track physicians within and across hospitals. Texas provides the state license numbers. During HCUP processing, the provided physician identifiers are encrypted.

Beginning in 2008, Virginia provided 4 physician ID fields: attending physician IDs, operating physician IDs, other physician1 IDs, and other physician2 IDs. All fields include both UPIN and NPI.

In Virginia, four encrypted physician identifiers are available:

1. Attending physician is provided in MDNUM1_S;
2. Operating physician that performed the first procedure is provided in MDNUM2_S;
3. Other physician 1 and other physician 2 are available in MDNUM3_S and MDNUM4_S.

Physician identification numbers can be used to track physicians within and across hospitals. Prior to 2007, Virginia only reported Unique Physician Identification Numbers (UPINs). Beginning in 2007, Virginia accepted 2 different physician ID numbers in these fields: UPIN and NPI. The inclusion of NPI increased the frequency of physician ID numbers provided in these fields. During HCUP processing, the reported physician identifiers are encrypted.

In Washington, two types of physician identifiers are available:

1. Attending physician is provided in MDNUM1_S and
2. Other physician is provided in MDNUM2_S.

Physician identification numbers do not accurately track physicians within and across hospitals. Washington collects several different types of physician identifiers, depending on the type of identifier provided by the hospitals. Hospitals provide Medicaid, Universal Physician Identification Numbers (UPINs), and DOH/HPQAD license numbers as physician identifiers. During HCUP processing, the physician identifiers are encrypted.