The diagnosis code identifying the beneficiary's principal diagnosis.
For ICD-9 diagnosis codes, this is a 3-5 digit numeric or alpha/numeric value; it can include leading zeros. 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.
Starting in 2011, with version J of the NCH claim layout, institutional claims can have up to 25 diagnosis codes (previously only 11 were accommodated), and the noninstitutional claims can have up to 12 diagnosis codes (previously only up to 8).
The lower the number, the more important the diagnosis in the patient treatment/billing (i.e., ICD_DGNS_CD1 is considered the primary diagnosis).