The Japanese Red Cross Society failed to recover blood donated by 37 people for transfusions even after it learned that a woman who received some of that blood became infected with hepatitis B, Red Cross officials said Saturday.

Five supply sets of the blood that went unrecovered by the Red Cross ended up transfused into patients. The society is checking the status of the recipients, the officials said.

According to the Red Cross, a woman in her 70s received a transfusion of blood from the 37 donors for treatment of leukemia between October and January. Her liver function deteriorated in March and she died the next month. Her hospital told the Red Cross in March that the woman may have been infected with hepatitis B through a transfusion.

The Red Cross conducted high-precision tests on other blood samples from the 37 donors that were kept at the society, but hepatitis B was not detected. The society did not test blood donated by the 37 already in circulation among medical institutions, the officials said.

Medical experts say that an amount of the virus too small to be detected by the advanced tests could cause hepatitis B.

The Red Cross, found last year to have overlooked blood tainted with the HIV virus, has since compiled guidelines for followup screening.