In simple terms, the digital test stick sucks up urine like a "regular" HPT. The test has a control line like every other HPT, to indicate the test worked properly. Then there is a "results zone" where a second line may or may not appear. Here's the difference: the second line may appear even if you are not pregnant, because the antibodies in the "results zone" are NOT testing ONLY for pregnancy hormone. Drumroll please. The "results zone" detects not only hCG (pregnancy hormone) . . . but also LH (luteinizing hormone.) LH is found in women's bodies almost all the time in some quantitity. (See the Fertility Info section for the nitty-gritty.) So, depending upon where you are in your cycle, how much LH your body produces normally (which can be thrown off by conditions like PCOS), you may see a second line even when there is no hCG ("Not Pregnant.")
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