Can anything affect a blood pregnancy test besides from testing too early?

Heterophile antibody: Presence of heterophile antibodies can affect results of blood tests for many items. It usually does not affect the urine test. If you miss your period by 4-5 days, do a home pregnancy test. If the result is negative repeat the test 4-5 days later unless you get a period by then. Use first morning urine and follow the instructions for the test carefully. If you do not wish to be pregnant, use contraception all the time, every time. You may consider implanted contraceptive, or IUD. Practice safe sex. Get HPV vaccine.