There are two types of blood tests to check for pregnancy – quantitative and qualitative beta human chorionic gonadotropin (beta-hCG) tests.
What is Qualitative HCG Blood Test
A qualitative beta-hCG test confirms the presence or absence of hCG in the blood. This test only confirms if a woman is pregnant or not. HCG levels of 25 mIU/mL and more is usually detected by this method.
What is a Quantitative HCG Blood Test
A quantitative beta-hCG test measures the exact amount of hCG in the blood and is a very sensitive test for pregnancy since even very small amounts of hCG can be detected by this test, even as low as 1 mIU/mL. However, this test is not done routinely and is not necessary in all pregnancies.
Quantitative HCG Levels and Reference Range
HCG levels increase rapidly in the first trimester of pregnancy and then gradually declines. The amount of beta-hCG detected will be a pointer to the stage of pregnancy. In early pregnancy, the amount of hCG (usually 1200 mIU/mL or less) doubles every two days, so serial blood tests may be conducted every 48 hours can determine if the pregnancy is proceeding normally or not. Even if it does not double, there should be at least a 66% increase in 48 hours. HCG levels between 1200 and 6000 mIU/mL double every 72 to 96 hours, while hCG levels above 6000 mIU/mL take over 4 days to double.
A quantitative test should not be conducted to gauge the stage of pregnancy but is rather used as a method of monitoring the progression of a healthy pregnancy in the first trimester. If the result is :
- less than 5mIU/mL then this is considered negative for pregnancy.
- between 5mIU/mL to 25mIU/mL is inconclusive and a repeat test is necessary.
- greater than 25mIU/mL confirms pregnancy.
Low Levels of Quantitative hCG Test
Information regarding viability of a pregnancy can be obtained by a serial quantitative hCG test. Falling hCG levels will indicate a non-viable pregnancy.
A serial quantitative hCG test which does not show the expected rise of hCG may indicate :
- An impending miscarriage (threatened abortion).
- Incomplete abortion.
- Complete abortion – after a miscarriage, the hCG level usually returns to the non-pregnant range in about 4 – 6 weeks but this will depend upon the stage of pregnancy when the miscarriage occurred.
- Ectopic pregnancy.
- Fetal death.
- Drugs such as diuretics and promethazine.
High levels of Quantitative hCG Test
HCG levels which are higher than normal may indicate :
- Multiple pregnancies such as twins or triplets.
- Normal pregnancy.
- Hydatidiform mole or molar pregnancy.
- Choriocarcinoma of the uterus.
- Cancer of the ovary.
- Drugs such as anticonvulsants, anti-Parkinson drugs, phenothiazine and promethazine.