The blood pregnancy test is a test that detects the amount of beta hCG in the blood, and is indicated to confirm pregnancy. It is typically considered positive when beta hCG levels are greater than 25 IU/L.
This test is usually carried out in the laboratory and can identify pregnancy in the first few weeks after intimate intercourse without a condom. However, false positive results can be caused by some tumors, such as breast or endometrial cancer, and changes in the immune system, for example.
In case of a positive or indeterminate result in the blood pregnancy test, it is recommended to consult an obstetrician and, if the pregnancy is confirmed, begin prenatal care.
Possible results
The blood pregnancy test result may be:
- Negative: beta hCG level is less than 5 IU/L;
- Undetermined: amount of beta hCG between 5 and 25 IU/L;
- Positive: beta hCG dosage greater than 25 IU/L.
Beta hCG levels in the blood increase during pregnancy and typically reach around 100,000 IU/L by the 10th week of pregnancy.
Gestational age calculator
Although it may not be a very accurate calculation, it is possible to calculate gestational age by taking into account the beta hCG values from the blood pregnancy test.
To find out your approximate gestational age, enter the beta hCG test result value into the calculator:
Changes in case of ectopic pregnancy
A blood pregnancy test may indicate an ectopic pregnancy when beta hCG levels stop rising before 8 weeks of pregnancy or rise more slowly than expected.
Furthermore, when the amount of beta hCG is greater than 3,500 IU/mL and the ultrasound does not find the baby inside the uterus, it may also be indicative of an ectopic pregnancy. Understand better what an ectopic pregnancy is and how to identify it.
False positive or false negative result
The blood pregnancy test result may be false positive in case of:
- Hydatidiform mole;
- Choriocarcinoma;
- Multiple myeloma;
- Some tumors, such as breast or endometrial cancer;
- Changes in the immune system, such as IgA deficiency or the presence of rheumatoid factor in the blood;
- Chronic kidney disease.
Furthermore, the blood test result can also be false negative in some cases, especially when it is done too early or when beta hCG levels are abnormally high.
Is the blood test better than the pharmacy test?
The blood pregnancy test is the best way to confirm pregnancy, as it shows the exact amount of beta hCG in the blood. This test is carried out in a laboratory and can identify even small concentrations of beta hCG, which could not be detected in a urinalysis.
Furthermore, the blood pregnancy test can be done after 8 to 10 days of intimate intercourse without a condom, giving an earlier result than pharmacy tests. See when and how to take the pharmacy pregnancy test.
Bibliography
- UPTODATE. Clinical manifestations and diagnosis of early pregnancy. Available at: <https://www.medilib.ir/uptodate/show/440>. Accessed on Nov 14, 2022
- PAGANA, Kathleen D; PAGANA, Timothy J; PAGANA, Theresa N. (1999). Mosby’s Diagnostic & Laboratory Test Reference. 12.ed. St. Louis, Missouri: Elsevier, 2015.
- STATPEARLS. Human Chorionic Gonadotropin. 2022. Available at: <https://www.ncbi.nlm.nih.gov/books/NBK532950/>. Accessed on Nov 14, 2022
- STATPEARLS. Early Pregnancy Diagnosis. 2022. Available at: <https://www.ncbi.nlm.nih.gov/books/NBK556135/>. Accessed on Nov 14, 2022
- HENDRIKS, Erin; ROSENBERG, Rachel; PRINE, Linda. Ectopic Pregnancy: Diagnosis and Management. Am Fam Physician. Vol.101, n.10. 599-606, 2020
