Seunga (Jasmine) Han, PharmD Candidate
Late Menstrual Cycle
Have you ever come across a situation where you had to use a pregnancy test kit? Was it because you were in fear of becoming pregnant after a late menstruation (commonly called a period)? Or did you use the kit in hopes of bearing a new life and starting a new chapter in your life? Regardless of the reason, this can be an overwhelming process for many females. So, to learn more about how the kits work as well as some tips on its usage, keep reading!
How Does It Work?
When an ovum (also known as an egg) gets fertilised, it takes about nine days before it’s implanted onto the endometrial wall of the female’s uterus. Upon implantation, a hormone called human chorionic gonadotropin (hCG) is detected in the blood and urine. Since only the placenta produces hCG, it’s a good marker for pregnancy in healthy females.1
Types of Pregnancy Testing
Before we get into learning how to use it, let’s take a look at the different types of tests available today.
Second generation tests use something called antibodies to detect hCG. If hCG is present, it gets sandwiched between two different antibodies – one attached to the test strip and the other attached to a color producing enzyme. This enzyme produces color when you test positive for pregnancy. These can detect hCG as early as the first day of a missed period and only takes 1 to 30 minutes to see the results.1
Third generation tests are the ones that are available for home use. Some examples include ClearBlue® and First Response®. They use the same mechanism for detecting hCG as second generation tests, except they’re more refined with higher accuracy and ease of use.1
How Do I Use It?
The most important tip is to follow the instructions provided by the manufacturer due to some variations that exist between the test kits such as:1
- Methods for collecting urine sample
- Length of time needed to apply urine sample to the stick
- Symbols indicating test results
Regardless of the test kits you use, the following are some useful tips:1
- Collect midstream urine sample to avoid contamination
- Urine sample may be collected in a small plastic cup or applied directly on the test stick during urination
- If urine is collected in a cup, a dropper is used to place small sample on the test stick or the absorbent end of the stick is placed into the cup for the amount of time mentioned in the manufacturer’s instruction
- If urine is applied to the stick directly, it’s important to place the absorbent end of the stick into the stream for the amount of time mentioned in the manufacturer’s instruction
- Wait with the result window facing up for the given amount of time indicated in the instructions
When Is the Best Time to Use A Pregnancy Test?
It’s recommended to test at least one day after a missed period and to use the first urine sample in the morning, which is when hCG levels are most concentrated. Since blood tests can detect levels as low as 1 mIU/mL, it can be used after a positive urine sample pregnancy test, which can detect levels between 20 – 100 mIU/mL, to confirm pregnancy.1
False-positive or False-negative Results
Regardless of the test kits, false-positives and false-negatives are possible, especially if the test is more difficult to use. Additionally, the timing of pregnancy test can play a role as well. Since sperm can survive in the Fallopian tube for up to five days after sexual intercourse and implantation of a fertilized egg can take another 6 – 12 days, false-negatives are possible for up to 17 days after sexual intercourse.1 As a result, a follow-up test several days later may be appropriate if the first test was negative.2 The following are some other errors that could lead to false results:1
- Expired test kit
- Not following the instruction
- Testing too early or late (after 60-70 days)
- Contamination in the urine such as soap residue, blood or protein
- Cloudy, pink or red urine
- Strong urine odour
- Warm or hot water rinse of the test surface before or after sampling
- Using fertility drugs containing hCG, hormones, or corticosteroids
- hCG production by tissues besides placenta
- Conducting pregnancy test within eight weeks of abortion
The Bottom Line
Pregnancy tests can be quite complicated, but it can be performed successfully if you carefully follow the manufacturer’s instructions and a few simple steps. Make sure to use midstream urine to avoid contamination and to test in the morning to ensure high concentrations of hCG in the urine sample. It’s ideal to use the test one day after your missed period, 8 weeks after abortion, and within 60 – 70 days after conception. Even though the test kits are very accurate, false results can occur with inappropriate use or timing. So, take a quick look at the list above for potential errors that could lead to false results and when you need to do a repeat test.
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- DynaMed Plus