A diagnosis code on the institutional encounter indicating the beneficiary's initial diagnosis at admission.
This diagnosis code may not be confirmed after the patient is evaluated; it may be different than the eventual diagnoses (e.g., as in PRNCPAL_DGNS_CD or ICD_DGNS_CD1-25).
On October 1, 2015 the conversion from the 9th version of the International Classification of Diseases (ICD-9-CM) to version 10 (ICD-10-CM) occurred. ICD-10 has more than 70,000 unique diagnosis codes compared to approximately 14,000 ICD-9 codes, which allows for more detail surrounding diagnoses.
Source: Medicare Advantage Organizations (MAOs)