In this chapter, based on blood samples recently analyzed, one of the four patients has a very low white blood cell (WBC) count. This is alarming since it might indicate the patient is suffering from a viral infection. Since all of the patients requested an STD test on their medical records, the students will specifically check for antibodies produced against the Human Immunodeficiency Virus (HIV). This Teacher Guide chapter highlights the Before the Lesson, During the Lesson, and After the Lesson instructions and recommends that the teacher read prior to starting the lesson. To learn more about the Student Edition chapter referenced here, check out “ Let’s Diagnose Them, Lab 4: HIV Test.”