A blood pregnancy test and home pregnancy test (urine test), both, help confirm pregnancy. The presence of hCG in blood determines whether a woman is pregnant or not. A blood test can detect human chorionic gonadotropin at much lower levels when compared to a urine test. A sperm cell fertilizes the egg in the fallopian tube. This fertilized egg moves down the tube and gets implanted in the uterus, within nine days of fertilization. Once the implantation occurs, the developing placenta starts releasing hCG in the bloodstream. Some hCG also gets passed in urine. This hormone can be detected in the blood before the first missed menstrual period, as early as six days after implantation.
hCG Blood Test
A blood pregnancy test can detect hCG levels as low as 2 - 5 IU/L, while most home urine tests detect levels of hCG as low as 100 IU/L (in fact, the range is 25 - 250 IU/L). Even though this test can detect very low levels of hCG, the hCG levels between 5 - 25 IU/L are considered inconclusive. Levels below 5 IU/L are truly negative, and the result is not considered positive unless the hCG level is 25 IU/L or above.
There are two types of blood pregnancy tests. They are Quantitative Blood Pregnancy Test and Qualitative Blood Pregnancy Test. The former measures the exact amount of hCG present in the blood, whereas the latter simply confirms the presence of hCG in the blood.
When To Perform The Test
There is a steady increase in the hCG levels throughout the first ten weeks of pregnancy. The hCG levels double about every 2 days for the first 4 - 6 weeks. This is the time when women often suspect that they are pregnant, and they might notice some early symptoms related to pregnancy. It is okay to undergo a test between the 4th and 6th week. The test can confirm a pregnancy about 7 days after ovulation (which is about a week before your period is due). It will yield a positive result, if 5 IU/L of hCG is found in the blood. This level is usually reached shortly after conception.
The woman may repeat the test after a few days, and compare the hCG values seen. HCG levels should show a rise and an upward pattern, as is expected in a normal pregnancy. If the levels of hCG do not follow the normal upward path, it might be an indicator of an abnormal pregnancy, an impending miscarriage, and sometimes an ectopic pregnancy. The hCG levels are only one clue; however, more tests need to be done to detect abnormalities. Physical examination of the woman, personal discussion, and other tests will help reach a definitive diagnosis.
Blood test Vs Urine Test
A quantitative blood test is the most accurate test of all, as it determines the exact quantity of hCG in the blood. The cost of a blood test is higher than urine test, as it has to be done in a doctor's office. The price may vary from doctor to doctor or from lab to lab. A urine test gives you instant results, while you have to wait for some hours or some days to get the results of the blood test. Intake of some medications, for example, promethazine, diuretics, hypnotics, etc., can affect the results. So, consultation with a doctor prior to the test, is essential.
If a blood pregnancy test is performed too early, it may give false negative results as there may not be enough hCG in the blood. This means, the test can be negative, when the woman is actually pregnant. If a woman taking medicines containing hCG undergoes a blood test, the test will be positive even though the woman is not pregnant. This is known as false positive result. So, it is necessary to inform your doctor about your routine medications, before undergoing a test.
Disclaimer: This HerHaleness article is for informative purposes only, and should not be used as a replacement for expert medical advice.