Urine Pregnancy Tests: False Results Explained
The Biomarker Handbook is a curated series that seeks to provide readers with insights on each biomarker we cover in our blood test packages and its relation to our body.
A missed period and early morning sickness are symptoms that hint a possible pregnancy, but certain laboratory tests are much more reliable and confirmatory than mere recognition of symptoms. The urine pregnancy test is one the first and the most convenient tests available that can confirm pregnancy as early as three weeks.
Urine Pregnancy Tests: How it Works
The urine pregnancy test, better known as simply the home pregnancy test, comes with a test strip that can detect the presence of the placental hormone, Human Chorionic Gonadotrophin (hCG) in the urine of a pregnant woman. This hormone is produced by the uterine linings of an expecting mother and its quantity normally doubles every two days after conception. The elevated level of this hormone in the urine of a pregnant woman is the basis of the urine pregnancy test.
The home pregnancy test can be performed in two ways – either by dipping the pregnancy stick into a fresh urine sample or by directly catching the midstream urine on the stick. Both ways produce 97% accurate results and are recommended to be done after the first day of the missed period.
The urine pregnancy kit contains a protein called the monoclonal antibody that reacts with the hCG in the urine and produces the classic ‘positive’ band seen in a typical pregnancy stick test. The second, constant band seen on the stick acts as a control to ensure the test kit is working.
Results in a Urine Pregnancy Test
Since there is a small chance of the urine pregnancy test failing, it is usually advised to take more than one pregnancy test after a few days interval.
A positive result in usually inferred by the presence of double bands, a color change or a plus symbol depending upon the kind of kit you use.
False Positive Results:
False positive result is when the test concludes positive for pregnancy, yet it isn’t the case in reality. Sometimes the result of the urine pregnancy test can show as positive before the onset of the menstrual flow a few days later. This false positive result can come about for a number of reasons.
The most common cause behind a seemingly false positive result is usually a very early miscarriage also known as a chemical pregnancy. Seemingly false positive because at the time of test taking, woman may well be pregnant or just losing the pregnancy but with still detectable levels of hCG in the urine. The statistics of miscarrying in the first trimester are high. Confirmed pregnancies have a 15 to 20% chance of miscarriage, whereas the figure can be much higher as many women suffer a miscarriage before they even realize they are pregnant.
Another explanation for a false positive result is checking the pregnancy stick after the given time frame (five minutes). This can result in the formation of urine evaporation lines that can cause the illusion of a double band (positive result) on the pregnancy kit.
Fertility trigger shots (injections) given to induce ovulation can also cause a false positive reading. These trigger shots use of hCG and the level of this hormone persists for some time before being washed out from the system. These persistent levels can give a false positive result on the pregnancy kit.
False Negative Results:
More commonly we tend to see so called false negative results. These results show negative on the pregnancy kit even when the woman is pregnant. Perhaps the most likely reason for a false negative result is testing too early. hCG, despite its rapid doubling rate, takes time to appear in detectable amounts in the urine. Taking the urine pregnancy test too early on might not detect appreciable amounts of hCG even in if the woman is pregnant.
Other probable causes for a false negative result are low sensitivity of the pregnancy kit used or the excessive dilution of urine. To avoid faulty results, it is recommended to use a good pregnancy kit and to take the early morning, midstream urine. Abstain from drinking any liquid before the test to avoid this diluted urine effect.
Urine vs. Blood Pregnancy Tests
While the home pregnancy tests are the most popular diagnostic tests used, there are certain blood pregnancy tests that can be performed even earlier to confirm pregnancy (as early as 14 days from conception). The blood pregnancy tests have a 98-99% accuracy and are the preferred option by women who want to find out if they are pregnant as soon as possible.
Blood pregnancy tests can be of two types: qualitative hCG test and the quantitative hCG blood test. The qualitative test gives a simple affirmation of pregnancy, while the quantitative blood test measures the exact amount of hCG in the blood.
Advantages of the blood pregnancy tests:
- Are the earliest possible tests that can confirm pregnancy
- Useful for tracking hCG in the blood of women with a history of miscarriages or other complications
- Quantitative blood tests are the most accurate pregnancy tests
Disadvantages of the blood pregnancy tests:
- Are generally more expensive than urine test kits
- Need to physically visit a clinic or a lab
- Results obtained in a longer time period
- Blood must be drawn to perform the test
The Pattern of Serum Quantitative hCG Levels in Pregnancy
hCG levels in the blood vary markedly every week. This level is measured in international units per liter. The typical pattern of hCG in the serum from the first day of your last menstrual period (LMP) is as follows:
At 3 weeks from LMP: 5-50 IU/L
At 4 weeks from LMP: 4-426 IU/L
At 5 weeks from LMP: 19-7,340 IU/L
At 6 weeks from LMP: 1,080-56,500 IU/L
At 7 – 8 weeks from LMP: 7,650-229,000 IU/L
At 9 – 12 weeks from LMP: 25,700-288,000 IU/L
At 13 – 16 weeks from LMP: 13,300-254,000 IU/L
At 17 – 24 weeks from LMP: 4,060-165,400 IU/L
At 25 – 40 weeks from LMP: 3,640-117,000 IU/L
Any abnormality in these levels or the rate of its increase (high-rising or low-rising) can be important to assess the condition of the placenta. Abnormal hCG levels are tracked by the doctor with frequent quantitative blood hCG and ultrasound.
Blood levels between 5-25 IU/L are thought to be equivocal for pregnancy, and a confirmatory repeat blood hCG quantitative levels is recommended in another 3 days.
When the hCG levels rise more than expected, your doctor may investigate for potential causes such as multiple pregnancy, a hydatiform mole, chorionic carcinoma, or it may also be a normal pregnancy.
When hCG levels are decreasing (more than expected), your doctor will investigate for threatened or missed abortion, a recent termination of pregnancy, or an ectopic pregnancy.
Signs and Symptoms of Pregnancy
Women who are pregnant might recognize these classic signs of early pregnancy:
- Nausea, Vomiting (morning sickness)
- Loss of appetite or increased food craving
- Swollen, tender breasts
- Mood swings
Managing Early Pregnancy with Diet
A healthy diet plays a crucial role in the proper development of the fetus. It is important to take balanced meals every day. The caloric requirement for a pregnant woman should increase by about 300 kcal/day. With twins, it should increase by 600 kcal/day.
A nutritious diet for pregnancy includes five portions of fruits and vegetables, carbohydrates, lean meats, eggs and other protein. Sugar, dairy products and excess salt intake should be reduced.
Dietary supplements are essential in the first and second trimesters of gestation. Folic acid (400 micrograms/day) and Vitamin D (10 micrograms/day) are recommended in the first trimester for the proper development of the central nervous system and the bones. Iron and calcium supplements are added only after 3 months.
It is recommended that women keep active and fit during pregnancy with regular exercises (low impact, non-contact, no risk of falling sports). Exercise is not dangerous to the baby. But do not over-exhaust yourself, keep your exertion to a comfortable level where you can always hold a conversation. And keep well hydrated.
When to See the Doctor
If you have missed a period or have the typical symptoms of an early pregnancy, it is a good idea to book an appointment with the doctor or purchase a home pregnancy test. If pregnancy has been confirmed, a follow up session with the doctor is essential.
Taking a home pregnancy test is the simplest and the most convenient way to confirm your pregnancy in the first few weeks of conception. It’s easy availability and accessible price is what makes it the most preferred diagnostic test for pregnancy worldwide.
If you want to find out more about pregnancy do’s and don’ts, and possible complications, read on about it in our lifestyle post here!
Interested in other biomarkers? Check out the rest of The Biomarker Handbook.
For more information, drop us a message and we will get back to you.