Questionable Medicare claims cost the Health and Human Services billions, the agency's watchdog has found.

Under Obamacare, physicians or other medical practitioners have to certify any beneficiaries who receive home health services and then document the encounter to receive Medicare reimbursements. This is to prevent fraud, according to the inspector general's report.

These encounters, known as "face-to-face" encounters, range from nursing care to physical therapy.

However, when the IG reviewed 664 face-to-face encounter documents of "home health agencies" that operated from January 2011 to December 2012, it found serious issues.

Thirty-two percent of the claims were either missing the face-to-face documentation all together, or lacked the full requirements. This resulted in "$2 billion in payments that should not have been made," the audit said.

Claims missing all of the documents were worth about $605.3 million. The remainder of the questionable claims were missing pieces such as signatures from a certifying physician or dates.

View the full report below.