What is a Serum Pregnancy Test?

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  • Written By: Mary McMahon
  • Edited By: Kristen Osborne
  • Last Modified Date: 23 October 2019
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A serum pregnancy test is a medical test performed to see if a patient is pregnant or to check on the viability of a pregnancy using a sample of the patient's blood. These tests are more sensitive and accurate than urine tests, although they are also slightly more invasive. They can also be used to detect a pregnancy slightly earlier than a urine test, an important consideration for some impatient expecting parents. This test can be administered in a hospital or clinic, and it may also be possible for a traveling doctor or nurse to attend a patient at home to take a blood sample.

For this test, a single vial of blood is drawn using sterile procedure. In a clinic or hospital with its own lab, serum pregnancy results can be returned very quickly. Otherwise, the sample may need to be sent out, and it can take a day or more for the results of a serum pregnancy test to come in.

In a serum pregnancy test, a sample of blood is drawn and tested for the presence of human chorionic gonadotropin (HCG), a hormone specifically associated with pregnancy. Qualitative tests look simply to see if the hormone is present, while a quantitative test will measure the amount of the hormone in the blood. Both tests are highly sensitive when done with blood, allowing doctors to detect very low levels of the hormone.


This hormone will start circulating in the blood and urine within seven to 10 days of conception. HCG levels rise very reliably and steadily over the course of a pregnancy, and checking hormone levels with a serum pregnancy test can provide information about how long someone has been pregnant, in addition to being used to determine the viability of a pregnancy. If a woman has two tests several days apart and the concentration of the hormone does not rise as expected, it can indicate that there is a problem with the pregnancy. Additional testing may be recommended to learn more about what is happening inside the patient's body.

The serum pregnancy test is also used after a miscarriage in follow-up appointments to check on the patient's progress, although the doctor may not call it a pregnancy test for reasons of sensitivity. The repeat testing is done to confirm that the miscarriage is complete and the woman's body is returning to normal hormone production after the termination of the pregnancy. If test results are abnormal, it may be necessary to do additional testing to find out why.


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Post 3

@fify-- That's not true. The serum pregnancy test will not be able to detect HCG levels until after seven days of pregnancy.

So you may definitely get a false negative if you get the test too soon. You have to wait some more and get the test again.

Normally the HCG levels in a woman who is not pregnant is zero. If the serum test shows HCG levels above 5 units, she is pregnant. But labs don't always take the same reference levels for pregnancy. So one lab might require HCG levels above 5 to consider the woman pregnant, while others will look for 10 units or more.

So it's a good idea to talk to the lab about what their reference values are for the HCG pregnancy test and when the best time is to get the test.

Post 2

@donasmrs-- That's a good question. Higher HCG levels are very apparent several weeks into the pregnancy. However, since the serum test is a very sensitive pregnancy test, it will still indicate higher than normal HCG within a few days of conception.

It would help to get a follow up test several weeks later if you still have doubts about being pregnant.

Post 1

If I get a serum HCG pregnancy test several days after conception and the test comes back negative, is it possible for it to be wrong?

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