In medicine, it might generally be best for tests to be negative (like tests for brain tumors or tests for sexually transmitted diseases, such as HIV -- as for medical histories, compare positive history) -- but not so in infertility. Infertility tests, such as the postcoital test, tests for ovulation, tests for tubal patency, and (not least) a pregnancy test, are generally better if they're positive.

A germ, or infective agent, responsible for infection of, and damage to, the fallopian tubes. In men particularly, chlamydial infection can cause nonspecific urethritis, with a feeling of burning during the passing of urine or with a yellow-colored discharge from the penis. In women, there can be a vaginal discharge or there can be mild or moderate abdominal pain from acute salpingitis; it should be suspected whenever there is yellow-colored mucus in the cervix during the taking of a Pap smear (i.e. when there is cervicitis). There might be no symptoms in either sex. The diagnosis of a current, untreated infection is made by testing cell scrapings from the canal of the cervix or from the urethra. As a germ, chlamydia is like a virus in some ways (it can grow only inside cells) and like a bacterium in others (it responds to some antibiotics -- especially tetracyclines and erythromycin). When it's diagnosed, both partners should be treated. A past infection can be revealed by measuring serum chlamydial antibodies, although false positive tests can occur.

(PCT) A test of: (1) receptiveness of the cervical mucus to sperm; and (2) sperm motility -- both of which are needed for the test to be a positive test. It's essential that the test be done to coincide with ovulation, tested with a urinary LH kit or measurements of serum estradiol (high), serum LH (preferably high) and serum progesterone (still low), because the job description of the cervical mucus at other times is to be impenetrable to sperm (i.e. the PCT will be negative for normal reasons).

A blood test to detect prior exposure to chlamydia. The antibodies commonly examined are not completely specific for the particular chlamydia organism that causes salpingitis and which is transmitted sexually: other chlamydia-like infections of the lungs and other regions of the body, and even some completely unrelated infections with non-chlamydial organisms can produce false positive tests; a negative test, that is an absence of detectable chlamydial antibodies, is however reassuring.

A screen for congenital abnormalities of the fetus done on the mother's blood serum during pregnancy to look for fetal trisomy, including Down syndrome. The original test comprised measurements of (1) serum alpha fetoprotein (decreased in the trisomies), (2) serum hCG (increased in trisomy 21, decreased in trisomy 18), and (3) serum estriol (decreased in trisomy 21, increased in trisomy 18). Note that only 60% of pregnancies with Down syndrome will be revealed by a triple test. Refinements have taken place, with 'free beta' (part of the hCG molecule) replacing hCG itself, and with the addition of PAPP-A replacing estriol, increasing the sensitivity and specificity of the test. Further gains in sensitivity and specificity comes from adding an ultrasound test for nuchal translucency. Even so, false positive tests are possible, which will be resolved only by performing CVS or amniocentesis, and so also are false negative tests, which means that CVS and amniocentesis should still be considered in otherwise high-risk situations.

A home test for ovulation in which the urine is tested for luteinising hormone. If the urine shows a positive test, ovulation will usually take place within 24 to 36 hours. Electronic devices that perform the same function are available (and are increasingly popular in the U.K.).