Occurrence code

Each occurrence entry pairs a code of two alphanumeric characters with a date in MMDDYY form, in form locators 31-34, and the a lines fill before the b lines. Form locators 35 and 36 hold occurrence span codes, which carry a from date and a through date for an event that lasted a stretch of time. The NUBC maintains both lists, and CMS’s own example shows the idea: a beneficiary whose Part A benefits ran out partway through a hospital stay is reported with code A3 and the date they were exhausted. When codes 01-04 or 24 are reported and another payer is involved, Medicare also wants the matching value code in form locators 39-41¹.

Dates drive the payment math. On a Medicare home health claim, occurrence code 50 carries the date the OASIS assessment for the period was completed, and a claim or adjustment without it goes back to the agency unless a disaster waiver is in effect. Codes 61 and 62 report a hospital or other inpatient discharge in the 14 days before the period’s from date. Medicare returns a claim that reports more than one of them, and the code reported feeds the grouper’s referral source input².

The mistake is the right code with the wrong date. An OASIS date that does not match the assessment, or a discharge outside the 14-day window, sends the claim back or changes how it groups. Take each date from the source record, the assessment or the discharge summary, rather than from the schedule.