U.S. health officials said on Tuesday they were re-evaluating rules that allow the testing of unapproved emergency treatments without patient consent, a practice that came under fire in recent studies of potential blood substitutes.

Critics attacked the Food and Drug Administration earlier this year for allowing Northfield Laboratories Inc. to study its experimental blood substitute, PolyHeme, in trauma patients without obtaining their permission first.

On Tuesday the FDA said a 1996 regulation allowed trials without consent only "under very strict circumstances" for patients with life-threatening conditions who are unconscious or otherwise unable to give their permission.

The agency said it was "taking a close look" at the rules and whether they adequately protected patients and encouraged or discouraged such research. Officials released updated guidelines on when and how such studies can be conducted and set an Oct. 11 hearing for public input.

"Unless the medical community can conduct studies in these life-threatening emergency situations, we may not truly have scientifically validated solutions to benefit patients in these extremely difficult circumstances," Dr. Janet Woodcock, FDA deputy commissioner for operations, said in a statement.

Nearly all clinical trials require that patients give their permission to be treated with an experimental product. FDA officials said they had received fewer than 60 requests since 1996 to waive the consent requirement and about one-third of those studies proceeded or were currently enrolling patients.

The review of the 1996 regulation had been in development before concerns emerged about the blood substitute studies, said Dr. Sara Goldkind, an FDA bioethicist.

In addition to the PolyHeme study, the U.S. Navy has requested FDA permission to test a similar product from Biopure Corp. called Hemopure in emergencies without patient consent.

Senate Finance Committee Chairman Charles Grassley, who has questioned the FDA's handling of the PolyHeme study, praised the agency's effort to re-examine the regulations.

"Anything that can be done to make sure people know they may be a guinea pig before they become a guinea pig in a clinical trial is welcome news. More transparency and clarity will benefit everyone," said Grassley, an Iowa Republican.

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