A Canberra woman who allegedly threatened security staff at a department store with a used syringe has been denied bail by the ACT Magistrates Court.

The Fraser woman was suspected of stealing up to $700 worth of clothes from the store, and was approached by security officers.

She then allegedly produced the needle, and claimed she was HIV-positive.

In escaping from the store, the woman is accused of approaching a car, claiming she was being chased by a group of men and needed help.

When the female driver refused the accused allegedly entered the car and held a 30-centimetre knife to her face.

The driver complied and dropped the accused off in Dickson.

The woman was apprehended later in the evening.

The court heard the woman had severe drug problems and Magistrate Glenn Theakston said the events "demonstrated how desperate she was".

Police say when she was apprehended she asked the officers for her needle so that she could have "a hit of heroin".

She did not enter a plea, and was remanded in custody.

She is set to appear in court next month.