Factors affecting results hCG may be present in blood up to four weeks after an abortion or miscarriage. The presence of hCG in blood or urine signals pregnancy. The simplest urine test is quick and inexpensive but is not accurate until at least two weeks after a missed period. Advantages It highly reliable. Blood tests are generally positive one to two weeks before urine tests.
Blood tests can detect hCG levels.
Urine tests are quick, inexpensive, and noninvasive. Disadvantages Urine tests may produce false-negative results a few days after conception. If result is positive, you should be scheduled for regular prenatal care. Published under license from Houghton Mifflin Company. Email This to a Friend.