It's 3 pm and you are finishing up your day in clinic.  A 25 year old female presents complaining of vaginal spotting for one day.  She has mid line abdominal pain which is similar to her menstrual cramps.  She performed a home pregnancy test and it was positive.  Her last menstrual period was 6 weeks ago.  You examine the patient and obtain the following information
 

• PMHx- none
• Gyn hx-  G₀,   chalmydia once previously,  unmarried
• Vital signs: 120/70  86  18  37
• General physical: unremarkable
• No fetal heart tones are present
• Abdomen:  mild supra pubic tenderness
• Pelvic: moderate blood in the vaginal vault, no tissue extruding from the os, which is closed.  The uterus is not palpably enlarged, no adnexal masses or tenderness are noted.  On Cervical motion the patient experiences discomfort on the right

B-HCG level 1200, Hct  37

You have heard that a serum progesterone level may be helpful in differentiating an ectopic pregnancy from an IUP.  You turn to your computer to get more information.

So you can structure your question as:

The test related outcome of interest is "accuracy"
The test of interest is serum progesterone
The disease of interest is ectopic pregnancy