Use Place of Service 31 if the patient is under a Part A skilled nursing stay.  Use Place of Service 32 if the patient is under a Part B long term stay. 

Place of Service 31 – Skilled Nursing Facility:  A facility which primarily provides inpatient skilled nursing care and related services to patients who require medical, nursing, or rehabilitative services but does not provide the level of care or treatment available in a hospital.

Place of Service 32 – Nursing Facility - A facility which primarily provides to residents skilled nursing care and related services for the rehabilitation of injured, disabled, or sick persons, or, on a regular basis, health-related care services above the level of custodial care to other than individuals with intellectual disabilities.

 Reference:  https://www.cms.gov/medicare/coding-billing/place-of-service-codes/code-sets

When seeing most patients in a nursing facility, practitioners must determine if the patient is under a long term Medicare Part B stay or a Part A skilled nursing facility stay. The reason this determination must be made is it changes the place of service code on the claim form. If the patient is under a long term Part B stay, Place of Service 32 must be used on the claim form. If the patient is under a Part A skilled nursing facility stay, Place of Service 31 must be used on the claim form.

A skilled nursing facility stay for Medicare beneficiaries is typically an inpatient rehabilitation stay following a qualifying inpatient hospital stay that was at least 3 days. Skilled nursing facility stays can normally be a maximum of only 100 days. Coverage for a skilled nursing facility stay typically requires one or more of intensive rehabilitation, continued medical supervision, or coordinated care from doctors and therapists working together. In order to use the correct place of service code on a claim form, practitioners who see patients in a nursing facility must determine if the patient is in the facility under a long term Medicare Part B stay or a Part A skilled nursing facility stay. This can be difficult because, in many cases, there are patients in the same building under these different admission types. There may even be two patients in the same hallway or in the same room as each other under these different admission types. Providers can make this determination by communicating with facility administrators. Additionally, some third party payers have online portals which providers can use to determine the admission status of patients in these types of facilities.