'Most other kits were far less sensitive - the five least sensitive tests couldn't detect hCG below concentrations of about 100 MIU/ml at their specified reading times. 'It detected hCG at concentrations as low as 6.5 mIU/ml (thousandths of an International Unit per milliliter) - that's almost sensitive enough to detect any pregnancy soon after implantation,' CR wrote. One kit, the First Response Early Result Pregnancy Test, emerged as the most reliable and sensitive test. 'Technicians read the results after the specified minimum wait - anywhere from 1 to 5 minutes, depending on the product - and then again at the maximum time allowed (10 minutes in all the products we tested).' Kits were rated on efficacy, ease of use, and ease of result readings. 'We conducted the tests as instructed on each product's package insert,' CR says. They tested each product at increasing levels of hCG concentration until a positive result was attained. Working with an independent laboratory that specializes in hCG studies, CR spiked hCG-free urine with varying concentrations of the hormone 'to mimic the range found in normal early pregnancies.' Regardless of collection method, reading the results is the same for every kit: if a line appears in the window after a specified number of minutes, the test is positive.

Concentrations of this pregnancy hormone vary widely from woman to woman, but the more sensitive tests can measure lower levels of hCG.Īll 18 brands tested by 'Consumer Reports' (CR) employ similar technology - most use sticks with absorbent wicks that are held directly in the urine stream, and most allow women to collect urine in a cup and then dip the stick.

All home pregnancy test kits use monoclonal antibodies to detect a hormone known as human chorionic gonadotropin (hCG), which is produced by the developing placenta beginning on the day on which the embryo implants in the uterine wall.

Super faint positive first response