Elevated levels of hCG in maternal serum and urine are both reliable indicators of pregnancy, which are used in pregnancy tests. hCG rises above the reference range by implantation approximately 6-12 days after conception.
Immunometric assays are used for the detection of both. Most immunoassays can quantify hCG as low as 1-2 mIU/ml.
These are qualitative immunoassay kits having detection limit of approximately 20 mIU/ml. hCG in urine is usually detected 2-3 days later than in the serum.
Strip is coated with a labelled antibody dye, which conjugates with hCG. There is a test zone and a control zone. When the strip is added to urine, the antibody dye conjugates with hCG to form antigen, antibody complex. This complex then binds anti hCG antibody in test zone and produces a colored zone. When the concentration of hCG is greater than 20 mIU/ml, unconjugated reagents bind coated antibodies in the control zone.
Preferably first voided urine in the morning. Random urine sample can also be used.
Collect urine in a clean, dry, plastic container. Perform test within 24 hours after collection of sample. If there is a delay, refrigerate the sample at 2-8 C.
Anti-hCG antibody coated strip is immersed in urine sample for about 3-5 seconds. Then we have to wait for 5 minutes for the results.
If only one colored band appears, the test will be negative.
When two colored bands appear, the test will be positive.