How long does pregnancy test kit detects hcg?

 
hCG is secreted into the blood almost immediately after implantation of the fertilised egg occurs. This hCG is excreted in urine and is the basis of the urine test for pregnancy. However, the test can only detect hCG after a certain minimum concentration is achieved in the urine. This happens approximately 6 weeks after the last menstrual period, or 2 weeks after the missed period. This is variable and the test may be positive earlier or later in different women. hCG can also be detected in blood. However, the urine test is simpler,cheaper and can be done at home.