What is the difference between a home pregnancy test and a blood pregnancy test?
Both a home pregnancy test and a blood pregnancy test measure HCG (human chorionic gonadotropin) the pregnancy hormone. Since HCG is only produced during pregnancy (except in the case of very rare tumors),
it is an extremely reliable sign of pregnancy. Obviously, home tests and blood tests differ in the way that they are performed, but they also differ in the amount of information they can provide.
Home pregnancy tests register the presence or absence of HCG. The test stick contains antibodies to HCG. If there is any HCG in your urine, it will be captured by the antibodies on the stick. In that case,
a pigment will be activated and a line (or, depending on the brand of test, a + sign) will appear. Since a home pregnancy test only registers the presence or absence of HCG, it cannot tell you anything about
the health of the pregnancy. It will still be positive in the case of a miscarriage or ectopic pregnancy, or even for days or week after a miscarriage. In addition, most home pregnancy tests cannot detect an
HCG level below 25. There is simply not enough HCG in the urine to make the test turn positive.
Blood pregnancy tests, however, are more sensitive. They can detect any amount of HCG from zero on up. Therefore, a blood pregnancy test will turn positive before a home pregnancy test. In fact, a blood
pregnancy test can turn positive approximately a week before you expect to get your period.
Blood pregnancy tests can also measure the exact amount of pregnancy hormone. There is no specific correlation between the amount of HCG and the weeks of pregnancy, so you cannot tell how far along you are based
on the level of HCG. The HCG level also cannot tell you about the health of the pregnancy.
However, there is an important relationship that provides information about the health of a pregnancy. In a normal pregnancy, the level of HCG should double approximately every 48 hours. If that does not happen, it is a sign that something is wrong. It could be a sign of a miscarriage that is going to happen, or it could be a sign of an ectopic pregnancy. In a miscarriage, the HCG level will rise slowly to a certain point, and then begin to fall. In an ectopic pregnancy, the HCG level can rise abnormally, fall and rise again. Since the rate of change is the important piece of information, at least two HCG levels must be tested at least 48 hours apart.
A positive result on a home pregnancy test is extremely accurate, so there is no need to confirm it with a blood pregnancy test. Blood pregnancy tests should be reserved for identifying very early pregnancies or determining the health of a pregnancy in the case of vaginal bleeding or spotting, abdominal pain or an abnormal ultrasound in the first trimester.