The Minneapolis Veterans Affairs Medical Center has been forced to postpone and reschedule dozens of surgical procedures through the end of the week after “an unidentified substance” was found in sterilizing equipment Wednesday.

Until the substance is identified and the equipment cleaned, inspected and certified, the Minneapolis VA has rescheduled most surgeries for the remainder of the week, the hospital said in a statement.

The VA said it is able to perform some cases at the medical center using other sterilizers that were not affected.

Patients were being contacted Wednesday.

Urgent and emergency procedures have been moved to other hospitals, including the University of Minnesota, according to a statement from the hospital.

The VA canceled 23 elective cases on Wednesday and 24 on Thursday. The VA said it is planning to do 11 cases at the medical center Thursday and then reassess on a daily basis, depending on the cases and available instruments.

“We are acting out of an overabundance of caution to ensure safe care for our veterans,” said Patrick Kelly, the director of the Minneapolis VA Health Care System, in a statement.

All the canceled cases were reviewed by a surgeon for urgency and rescheduled according to the clinically indicated date, the hospital said. Meanwhile, the hospital is using sterilizers at St. Cloud VA and Hennepin County Medical Center until its sterilizers are fully operational.

The VA said the problem was discovered by staff monitoring the equipment.

The substance has been sent to a laboratory for analysis.

A Denver VA hospital was forced to shut down its surgical unit temporarily last year after trace mineral deposits were found on some surgical tools. Surgeries were also rescheduled in 2010 after dirty surgical tools were discovered at John Cochran VA Hospital in St. Louis.

A 2011 Government Accountability Office report revealed systemic deficiencies in sanitation and sterilization procedures at VA medical centers across the country, potentially jeopardizing the health and safety of millions of veterans who rely on the VA for health care. Many medical centers failed to develop training programs to teach staff how to correctly clean, disinfect and sterilize reusable medical equipment, like surgical equipment, the report said. As a result, staff may not be sterilizing reusable equipment correctly, creating a serious medical risk. The Minneapolis VA was not cited as an offending medical center in that report.