Pregnancy tests can be performed on blood or urine. However, there are certain differences between the two types.
While urine pregnancy tests are qualitative (they only indicate the presence or absence of hCG hormone), blood tests are generally quantitative (they give an exact value of hCG hormone).
In addition, blood pregnancy tests are more sensitive. This means that they can detect smaller amounts of hormone, which decreases the likelihood of getting a false negative. In contrast, urine tests usually require higher concentrations of hormone in order to give a positive result.