Excision

The film depicts the life of a disturbed and delusional high school student, Pauline (AnnaLynne McCord), with aspirations of a career in medicine and the extremes to which she goes to earn the approval of her controlling mother. Pauline has a younger sister named Grace (Ariel Winter) who suffers from cystic fibrosis. Pauline has vivid dreams about herself and others being mutilated with excessive amounts of blood; and after each dream wakes panting in an orgasmic state.
Pauline decides to lose her virginity to a boy named Adam - explaining what she wants from him and gives him her number. Because of her fascination with blood she arranges their meeting while she is on her period. While having an orgasm she imagines herself choking Adam and the bed filling with blood. At the end she asks Adam to go down on her, which he obliges. After a few moments he runs to the bathroom disgusted by the blood, as he was unaware she was on her period.
During sex class, Pauline takes a sample of her blood and puts it under a microscope to check for STDs. Later on she sees Adam on the bleachers with his girlfriend. She tells Adam she doesn't have any STDs and asks his girlfriend if she has any, who states that she doesn't. Pauline then tells them that if the girlfriend doesn't have anything neither will she. After she walks away Adam's girlfriend deduces that he was unfaithful.
Across the street from Pauline and Grace is a teenage girl who jumps rope in her drive way. Pauline invites the girl to jump rope with her, but she finds Pauline weird and refuses. Grace defends her sister and storms off, pulling Pauline with her. Adam's now ex-girlfriend and her friend TP Pauline's house and spray paint 'cunt' and 'whore' on it. Pauline, on an angry tirade at school, pushes Adam to the ground and slams his ex-girlfriend's face into her locker, resulting in her being expelled from school.
While in her room she overhears her parents saying Grace's doctor wants her on the lung transplant list. During dinner that night her sister has a severe coughing fit, which concerns her parents. In the morning their mother leaves and the father stays home. Pauline drugs her father with tea and when he falls asleep, ties him up and gags him. Pauline then lures the jump roping girl to the backyard under the false premise that there are several jump ropes she can have that Grace can no longer use because of her lungs. She places a cloth over her mouth and after a brief struggle the girl loses consciousness. Pauline talks to Grace and lovingly strokes her hair, stating that Grace may be confused by what is going to happen but she has only her best interest in mind. She drugs Grace with the same cloth, then cuts and shaves her own hair.
In the garage, Pauline has cut open both girls and continues with her surgery, moving the healthy girl's lungs into her sister and placing the other lungs on ice, then sewing them both up. Pauline's mother arrives home and sees her husband tied up. She panics and runs through the house frantically screaming for Grace. She opens the garage door and finds Pauline with the bodies. Pauline explains that it is her first surgery, and although it is messy, it is wonderful, and that she was unsure what to do with the jump roping girl's body so she used her to practice her incisions. She then urges her mother to take a closer look, who runs towards her and grabs her, holding her and screaming hysterically. Pauline at first seems proud, but then begins to sob.

Question: Who takes a sample of her blood and puts it under a microscope to check for STDs
Answer: Pauline