The serial child killer was admitted to Fazakerley Hospital, in Aintree, for tests on Monday after becoming "acutely physically unwell".
The 74 year old who was jailed along with his partner Myra Hindley for kidnapping and murdering five children, has been detained at Ashworth high security psychiatric hospital in Maghull, Merseyside, since 1985.
The pair They lured children and teenagers to their deaths, with the victims sexually tortured before being buried on Saddleworth Moor above Manchester.
A spokeswoman for Ashworth said:
"Ian Brady, a patient at Ashworth Hospital, is still in a general hospital this morning where he spent the night after becoming acutely physically unwell. He has undergone a series of tests and was kept in. Ian Brady is in a single room and will continue to be accompanied in that room at all times by two nurses from Ashworth Hospital. Two other members of Ashworth Hospital staff will also be on duty outside his room throughout his stay in the general hospital."
Brady is due to attend a mental health tribunal on Monday regarding his application to be transferred to a Scottish prison and be allowed to die, but his appearance at that hearing is now in doubt.
Brady was given life at Chester Assizes in 1966 for the murders of John Kilbride, Lesley Ann Downey and Edward Evans. Hindley was convicted of killing Lesley Ann and Edward and shielding Brady after John's murder, and also jailed for life. In 1987 the pair finally admitted killing Keith Bennett and Pauline Reade.
Both were taken back to Saddleworth Moor in 1987 to help police find the remains of the missing victims but only Pauline's body was found. Hindley died in jail in November 2002, aged 60.