When testing blood, erroneous results are possible (about 2%), but most often additional examinations are necessary to confirm the diagnosis.
False positive.
The woman has elevated hCG in the blood, but there is no developing fetus on ultrasound. This happens in cases where, before the analysis, drugs were used to stimulate ovulation, or hormonal drugs were prescribed.
Usually the doctor recommends repeating the hCG determination after 3-5 days. If there are still high indicators, but they do not correspond to the expected period, then you need to look for a tumor.
False negative.
The analysis did not detect an existing pregnancy. This is possible in a very short period of time - no more than 8 days have passed since ovulation. The second reason is a violation of the attachment of the fertilized egg; if it is located outside the uterus, then hCG does not grow in the required quantity. The same situation occurs when fetal development stops and there is a threat of miscarriage.
A blood test for hCG helps determine the presence of pregnancy. It is more informative than test strips. Hormone determination is also required if neoplasms are suspected, to monitor a developing pregnancy.
We recommend reading the article about how much hormone testing is done. From it you will learn about how many tests are done in gynecology and how long to wait for the results of hormone tests in the clinic.
This is especially important if the previous ones had complications or there is a risk of chromosomal diseases of the fetus. For the result to be reliable, preparation is required. In case of deviations from the norm, additional examination is necessary, since the rise and fall of the hormone is not the main diagnostic sign. There is a possibility of false results when detecting pregnancy.