When urine is collected on the test strip of a home pregnancy test, it then moves across the strip by way of wicking action. Stretched across the test strip is a membrane made of nitrocellulose, a material used because it assists the movement of proteins. As the urine comes into contact with the membrane, it mixes with colored particles present in the nitrocellulose. Then, as the mixture of urine and color moves along the membrane, it comes in contact with a test line. This line contains antibodies for the hcG which, if they come into contact with the mixture, will trap particles in place, creating a colored line. When the liquid moves to the end of the membrane, the color solution is caught at a second test line. This line also contains an antibody, but this antibody will catch the color particles whether or not the solution contains hcG. This means that the second line will appear for both positive and negative results, but if both lines appear, the test is confirmed positive.
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