Why does hcg never enter a womens urine in some women?

Hcg in urine: Hcg, human chorionic gonadotropin, is found in blood of men and women. It is very elevated in pregnancy and some forms of cancer. Urine pregnancy tests are designed to detect the presence of HCG in the urine of pregnant women. It is found in all pregnant women. However, it has to reach a threshold to be detectable and if urine is checked too early in pregnancy, the test may be negative.