Which is better if I want to know if I am pregnant – the urine test or the blood test?
The most important difference between urine tests and blood tests are that the blood test can tell you are pregnant earlier. A blood test may pick up hCG a week after conception, whereas urine tests may not pick up hCG until about a week later – that is, at the time of the first missed menstrual period.
As long as the tests are not done too early, you would normally get the same result whether you have a urine test at home, in the doctor’s office or in a laboratory, or a blood test done in the laboratory. However you may get different results if you do a urine test at home too early in the pregnancy, when it is still negative, then go to the doctor a few days later, when the result of a urine or blood test may be positive.
The urine test you do at home is convenient and private and avoids having a blood test, but it is important to follow the directions extremely carefully. The test should be done on a first morning urine sample before you have drunk a lot of fluid.
Can the test result be wrong?
If a blood or urine test is done too early in pregnancy, when the hCG level in the body is still low, it is possible to get a result.
Urine tests may also give false-negative results if the urine is very dilute, so you should not drink a lot of fluid before collecting a urine sample for a pregnancy test.
Urine tests may give results if you have blood or protein in the urine, for example if you have a urinary tract infection. The urine test result can be wrong if you are taking certain medicines – some medicines cause a false-positive result and some a false-negative.
The blood test result can occasionally be wrong because of something in your bloodstream that interferes with the test, including certain types of that may give a false-positive result.
If you or your doctor thinks the blood or urine test result is wrong, you can ask the laboratory to measure your hCG level using a different test method.
It is also possible for a woman who is not pregnant to have hCG in her bloodstream at a level suggesting very early pregnancy. This tends to happen when women are tested at around the time of menopause. This is because hCG can be produced by the pituitary, a gland at the base of the brain. This is not harmful and does not indicate disease. To check whether or not the woman is pregnant, the test can be repeated in 2 days. If she is pregnant, the hCG should be approximately double what it was the first time it was tested. If she is not pregnant, the level shouldn’t change much.
What is an ectopic pregnancy?
An ectopic pregnancy is the condition when the fertilised egg implants somewhere other than in the womb. This is a serious condition needing immediate treatment. Women with ectopic pregnancies often have abdominal pain and uterine bleeding. A woman with an ectopic pregnancy will still have a positive pregnancy test because their placenta produces hCG. However, the level may be lower than in a healthy pregnancy.
When is a blood hCG test requested instead of a urine hCG?
To tell if a woman is pregnant or not, usually a urine test will give the answer, unless it is very early in the pregnancy (say, before the first missed period), in which case a blood test is needed. However, a blood test is needed if a doctor is concerned that something is going wrong the pregnancy, and he or she wants to know the actual amount of hCG in the blood. Blood tests for hCG are also needed to monitor people with trophoblastic disease (tumours developing from the placenta during pregnancy) or germ cell tumours (tumours developing from the sperm in males or egg in females).
How long after a miscarriage would it take for a pregnancy test to show a negative result?
It really depends what the hCG level in the blood was at the time of the miscarriage, but both urine and blood tests for hCG usually become negative within a few weeks of a miscarriage.