Hello i am Allana , i took a home pregnancy test last thursday evening it was positive with a light second line showing , so i waited till morning and used a diffrent btand of jome pregnancy test and showed negative then i waited till after 8am , and took another test with a different brabd , and showed positive with the second line light but viewable , then i took one this morning early and showed negative , does smoking cause low HCG readings in home pregnacy tests ?