Clearblue ovulation tests are available in both digital and non-digital formats. The tests detect the presence of luteinizing hormone in the urine. This hormone increases dramatically, referred to as "surging," at the time of ovulation. The LH surge triggers the release of matured eggs from ovarian follicles, and the woman is then fertile. Using a Clearblue ovulation test to pinpoint the time of the LH surge allows a woman to time intercourse or insemination to her most fertile period, increasing the chances of becoming pregnant.
Consult the chart included with the Clearblue ovulation test to determine what day testing should begin. Women with longer menstrual cycles will begin testing later than other women, and women with shorter menstrual cycles will begin sooner. A woman with a 21 day cycle will begin testing for ovulation on cycle day 5, where a woman with a 40 day cycle will begin testing on cycle day 23. To determine cycle length, use the shortest cycle in the last six months as your guideline.
Test the amount of LH. Clearblue's instructions state that the ovulation tests can be used at any time during the day, but sources such as peeonastick.com state that LH is not synthesized until later in the day and the ideal test time is between 2 and 4 p.m. Open the test strip packet and hold the wick end of the test in the urine stream for 20 seconds. If using a non-digital test, a reference line will appear to show the test is working.
Read the results of the test after three minutes. On non-digital tests, a test line that is the same color or darker than the reference line indicates a positive result. For digital tests, a smile appears in the digital readout window when the test is positive. Positive results mean the LH surge has been detected, which is the signal for the start of ovulation. The follicle will rupture and the egg will be released usually within 12 to 24 hours of the LH surge. A woman's fertile period begins about 24 to 36 hours before ovulation and lasts until 24 hours after ovulation, after which the egg is no longer viable.
If the test results are negative, the line will be lighter than the reference line for non-digital tests. On digital tests, a circle will appear. Repeat testing with a new test. Tests may be repeated more than once per day, or at the same time every day on consecutive days.
Women who are taking fertility drugs containing luteinizing hormone or human chorionic gonadotropin should not use ovulation tests as the results may not be accurate.
Pregnant women may also receive a false positive result on a Clearblue ovulation test.