This Wall Street Journal investigation shows how hospitals, to maximize their Medicare revenue in the face of federal efforts to reduce readmissions, use ingenious billing tactics.

The story notes that “Patients on observation status can remain in the hospital for days, and typically receive care that is indistinguishable from inpatient stays, experts say. But under Medicare billing rules, the stays are considered outpatient visits, and as such, don’t trigger penalties under the health law.

“The Journal’s analysis of Medicare billing data shows that increases in observation stays can skew the readmission numbers, letting hospitals avoid penalties even if patients continue to have complications and return for repeat visits. Observation stays generally are cheaper for the government, but in some cases they can lead to big bills that are the patient’s responsibility.”