What's 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, 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.

A home pregnancy 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 line (or, depending on the brand of test, a + sign) will appear. Most home pregnancy tests can't detect an HCG level below 25. There is simply not enough HCG in the urine to make the test turn positive.

Blood pregnancy tests, 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. In a normal pregnancy, the level of HCG should double about 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 (tubal) 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 are needed only for finding very early pregnancies or checking the health of a pregnancy in the case of vaginal bleeding or spotting, abdominal pain or an abnormal ultrasound in the first trimester.