Health chiefs have admitted they failed to meet standards for decontaminating medical equipment.
Hounslow Primary Care Trust met 41 of the 43 government criteria on which providers are judged, according to its own assessment published today.
But it was among more than a fifth of trusts which failed to ensure re-usable equipment was thoroughly cleaned.
The other area in which the trust fell short was supporting the development of staff and ensuring it employed enough people from ethnic minorities, though bosses claim they have now resolved those issues.
West Middlesex Hospital also met 41 out of 43 criteria, according to statistics released by the Healthcare Commission.
The hospital claimed it did not have sufficient information to assure it consistently responded to patients' concerns and met standards on research.
Both trusts fell slightly below the national average of 95.7 per cent when it came to meeting the targets.
The Healthcare Commission will attempt to verify the results by carrying out a series of spotchecks before publishing its annual performance ratings in October.