Starting in 2008, person identifiers (PNUM and PNUM_R) are no longer available in the Arizona files. Patients cannot be tracked after 2007.

Due to technical difficulties at the data source, the person number (PNUM and PNUM_R) is not available in Arizona from July 1, 2002 to December 31, 2002. The encrypted person identifier (PNUM_R) may not accurately track patients across hospitals. Arizona accepts social security numbers, health insurance claim numbers, and certificate numbers as person identifiers. No documentation was available about the consistency of coding within and across hospitals.

In Arkansas, the re-identified person number (PNUM_R) is based on encrypted social security numbers.

California reports encrypted social security numbers as person numbers.

Beginning in 2010, Iowa provides a patient identification number. Social security number (SSN), birth date, and gender are used to create a patient identifier. A patient identifier is not assigned if any of the three fields are missing or invalid (e.g., the SSN is not nine digits or is filled with a recurring character).

Beginning in 2013, Iowa provides a new unique ID that is develop using probabilistic matching based on name, gender and date of birth.

Beginning 2017, Iowa changed their coding scheme for person numbers. Therefore, they cannot be used to track patients in prior years.

In 2013, Maryland began providing a new statewide encrypted unique patient identification number (CRISP_EID) to link patients across all hospitals.

In 2012, Maryland provided HCUP with an Enterprise Master Patient Identifier (EMPI). This is a hospital system enterprise identifier, also known as the master patient identifier, that produces is a unique patient identification number using a probabilistic matching algorithm and is used to link patients across system hospitals only. For 2012, the EMPI value is populated for 19% of the inpatient records. The supplied identifiers are encrypted during HCUP processing.

Beginning in 2013, Mississippi provides a new unique ID that is developed using probabilistic matching based on name, gender and date of birth.

Beginning in 2010, Mississippi provides a patient identification number, which are supplied as encrypted social security numbers. The supplied identifiers are encrypted again during HCUP processing (PNUM_R).

Nevada generated and provided a unique patient number from 2002 to 2008. In 2013, Nevada implemented a new method and began providing this encrypted unique patient identification number.

New Mexico changed their coding for person numbers in 2013; they cannot be used to track patients between 2013 and prior years. Coding scheme for person numbers is inconsistent from year to year. Therefore, they cannot be used to track patients across years.

North Carolina provides an encrypted social security number. Reporting of the patient's social security number is optional for hospitals in North Carolina. Beginning in the 2000 data, this data element is frequently missing. During HCUP processing, this identifier is re-encrypted.

Washington had changed their formats for person numbers in 2009 so they will not be able to be linked with previous years. Starting in 2010, Washington only provides the data element visitLink as synthetic patient identifier.

The Washington person number (PNUM_R) cannot be used to track patients consistently over time because the coding scheme changed.

In 2008, Washington changed their format again for PNUM_R and it is being loaded from Washington's Revisit file. They are using a probabilistic linking method to unduplicate the file (LinkPlus for UB04 records and Automatch for UB92 records). They assign a random number to the unique patient groups with a SAS program, sort by the random number, and then assign each unique patient a number beginning with 1. They discovered a very large number of cases where hospitals are reporting the following names for infants: BABY, BABY BOY, BABY GIRL, BABYBOY, BABYGIRL, BB-, BBABY, BG-, and INFANT. Since infants from multiple births will have the same last name and the same date of birth, identifying revisits may incorrectly assign infants of multiple births as revisits. They also link their hospitalization data to our birth data and they plan to identify revisits for infants by replacing the infant name from the linked birth record with the name reported in the hospitalization data. This means that infants will not be linked until a later date. Since discharges for some of the infants does not occur until the first quarter of next year, their birth linkages will not be done until after they release the first quarter data for a year.

In 2007, Washington changed their format for PNUM_R. Patient's first 4 letters of the last name, first 3 letters of the first name, middle initial, and last 4 digits of SSN. If part of a name or SSN is missing, then it is filled in with dashes (-).

Prior to 2007, Washington used the first two characters of the patient's last name, the first two characters of the first name, and the birth date to create an encrypted person identifier. People with similar names and the same birth date may have the same identifier.

Prior to 1990, one person may have the two different values of the encrypted person number across time. The state reports that before 1990 some hospitals did not follow the patient number convention and assigned this identifier based on the last two letters of patients' first and last names, rather than the first two letters. Starting in 1990, all hospitals followed the same conventions.