Home pregnancy tests work by detecting pregnancy hormone in woman s body, a hormone called human Chorionic gonadotropin (HCG). Shortly after a fertilized egg attaches to your uterine lining, woman's body starts to produce this hormone, and home pregnancy tests can predict with quite good certainty whether woman is pregnancy or not. HCG increases in body rapidly after first 2 weeks of pregnancy, so pregnancy test will definitely detect the hormone after 2 weeks of conception. On the other hand, more precise and more sensitive blood test to detect HCG can be done earlier in your doctor's office. Although most home pregnancy tests work in the same fashion, there are different types of tests. For this reason, in case of confusing results, it is recommendable to try another brand, and despite the fact that most tests work in a similar way, always check instructions on the kit, because instructions may vary slightly from kit to kit.
Yes, home pregnancy tests are not 100% accurate and home pregnancy tests can be wrong. The experience if taking a home pregnancy test can be a nerve wracking experience and you are basically never sure whether trust the results or not. Most often when pregnancy tests are wrong, or can be wrong, is at the start of a pregnancy. The main reason for this is because some women develop amounts of pregnancy hormones that are detectable (and pregnancy test shows positive for pregnancy), while other women do not have detectable pregnancy hormones in their body in early pregnancy (at least detectable by home pregnancy test). Besides, it is also not advisable to take home pregnancy test right after missing period. Wait at least one week because a negative result shortly after missed period might be wrong, and showing you are not pregnant does not necessarily mean that.