A strip pregnancy test is a qualitative assay designed to detect Human Chorionic Gonadotropin (HCG) in a urine sample. HCG is produced by the placenta shortly after a fertilized egg implants into the uterine lining. The test uses embedded antibodies that bind specifically to HCG molecules, resulting in a color change to indicate a result. Strip tests are widely accessible and cost-effective compared to midstream or digital home pregnancy tests.
Optimal Testing Time
The timing of a strip test directly influences its accuracy because the test relies on a sufficient concentration of HCG in the urine. HCG levels begin to rise significantly only after implantation, which can happen between six and twelve days after conception. Testing too early, before the concentration of HCG has reached the test’s detection threshold (often 25 mIU/mL), can lead to a false negative result.
For the most reliable reading, wait until the first day of a missed menstrual period or several days after the expected start date. Using First Morning Urine (FMU) is highly recommended, especially in the earliest stages of testing. HCG concentration is highest in the morning because the urine has accumulated overnight, maximizing the test’s sensitivity.
Step-by-Step Procedure
Before beginning, carefully read the manufacturer’s instructions, as timing and dipping duration vary between brands. Check the expiration date on the foil pouch to ensure the chemical reagents are active. You will also need a clean, dry container and a timer ready for use.
Collect a sufficient amount of urine in the container, ensuring the cup is stable. This collection method is necessary because strip tests are not designed to be held directly in the urine stream. The collected sample must be at room temperature for the test to function correctly.
Remove the test strip from its sealed pouch, holding it by the non-absorbent end. The strip has an arrow or a “MAX” line near the absorbent tip, indicating the maximum immersion depth. Immediately dip the absorbent end vertically into the collected urine for the exact duration specified in the instructions, typically five to ten seconds.
Do not immerse the strip beyond the maximum line. Exceeding this depth can flood the test window and compromise the capillary action, resulting in an invalid test. After dipping, remove the strip and place it flat on a clean, dry, non-absorbent surface. Set your timer for the manufacturer’s recommended reaction time, generally three to five minutes, and avoid disturbing the strip while the urine migrates.
Understanding Test Results
Once the waiting period is complete, read the result by examining the test window. All valid strip tests display at least one colored line in the Control (C) region. This confirms the strip functioned correctly and absorbed enough urine. If no line appears in the Control region, the test is invalid, and you must repeat the procedure with a new strip.
A positive result is indicated by two distinct colored lines: one in the Control (C) region and a second line in the Test (T) region. The color intensity of the Test line does not matter; even a faint Test line should be interpreted as positive, signifying HCG detection. A negative result shows only one colored line in the Control (C) region, meaning HCG was not detected above the sensitivity threshold.
If the result is positive, contact a healthcare provider to confirm the pregnancy and discuss prenatal care. If the result is negative but your period remains missed, wait 48 to 72 hours and retest. HCG levels double approximately every two to three days in early pregnancy.