A nurse working with Lucy Letby when a baby was allegedly poisoned has denied adding anything to his feed bag.
Letby, 32, is said to have tried to murder the premature twin by intentionally giving him insulin on the Countess of Chester Hospital’s neonatal unit.
The prosecution say she struck after midnight on a night shift starting on 4 August 2015 as the youngster, referred to as child F, received a new feed of nutrients via a bag connected to an intravenous line.
On Monday, the jury at Manchester Crown Court was shown a form signed by Letby and her colleague confirming the nutrient bag was changed at 12.25am on 5 August.
The colleague, who cannot be named for legal reasons, said she had no recollection of the specific event and could not be sure whether it was Letby or her who put up the bag.
Philip Astbury, prosecuting, asked the nurse if she had put anything in the nutrient bag.
She replied: "Absolutely not."
She also answered "no" when asked if she gave child F any insulin at any stage during that shift, in any way.
The court was shown messages sent between the witness and Letby after their night shift, in which they agreed child F was a "worry" and Letby said: "Something isn’t right if he’s dropping like that."
The nurse said child F’s observations had been "within normal limits" before midnight.
She said: "I was really happy with him."
She told the court tests from the earlier part of her shift showed he had a "good blood sugar level" and no concerns were raised when she had a handover at the start of her night shift.
She said: "He’d been nice and stable for me in the evening and, in fact, in the earlier part of the evening when I wasn’t there you can see the recordings are all within a similar level that we were happy with."
At a point between midnight and 1am, the child’s heart rate and breathing rate "suddenly" went up to concerning levels, the court heard.
She agreed the change was worrying, and added: "Especially in the context that you can see from above they (his levels) have been nice and steady and stable for a while."
The nurse said she asked a doctor to review the baby and tests showed his glucose level was "dangerously low".
The court has heard his glucose levels remained low on the day shift of 5 August even after the intravenous line, and a connected bag containing nutrients, needed to be replaced after swelling to child F’s leg.
Child F’s blood glucose rose to safe levels later that evening after the nutrients were stopped and extra sugar was given independently, the court was told.
He went on to make a full recovery and was later discharged.
Last week, three other colleagues - Shelley Tomlins, Sophie Ellis and Belinda Williamson - also denied giving insulin to the baby.
Letby is accused of trying to kill child F less than 24 hours after she allegedly murdered his twin brother, child E, by injecting air into his bloodstream.
The defendant, originally from Hereford, denies murdering seven babies and the attempted murders of 10 others between June 2015 and June 2016.
The trial will continue on Tuesday.