Why Does a Pregnancy Test Display Two Lines When a Blood Test Indicates Negativity?

If one does not desire children, it is crucial to take contraceptive measures during sexual intercourse to avoid unintended pregnancy. After engaging in sexual activity, to determine whether pregnancy has occurred, the first step is to observe whether menstruation has ceased. If menstruation has stopped, a pregnancy test strip can be used to initially ascertain pregnancy. However, due to various factors, the results of these strips may not be entirely accurate. Let's delve into the scenario where a pregnancy test strip indicates two lines, yet blood tests reveal no pregnancy.

I. What Does It Mean When a Pregnancy Test Strip Shows Two Lines but Blood Tests Indicate No Pregnancy?

1. Pregnancy test strips are prone to errors. If pregnancy is suspected, it is advisable to undergo a thorough examination at a hospital. This can also help with early planning. Blood tests for HCG (Human Chorionic Gonadotropin) can be conducted 7-10 days after sexual intercourse to accurately and early determine pregnancy.

2. This medical phenomenon is known as pseudocyesis, where pregnancy symptoms are present despite no actual pregnancy. It is caused by endocrine imbalances or psychological factors such as eagerness for pregnancy or stress. In such cases, the body may self-correct over time, or medical advice and medication can be sought.

3. Ensure that the pregnancy test strip is not expired or of poor quality. Check the expiration date on the packaging. Expired or improperly stored strips can yield inaccurate results. Additionally, testing in the evening may reduce accuracy; using morning urine tends to yield more precise results.

II. How to Interpret Pregnancy Test Strips?

Negative: A single purple line (control line C) in the test area indicates no pregnancy.

Positive: Two purple lines (control line C and test line T) in the test area indicate pregnancy. The intensity of the test line varies with HCG levels at different stages of pregnancy.

Invalid: No purple line or only the test line T appearing in the test area signifies a failed test or an invalid strip, requiring a retest.

III. Precautions for Using Pregnancy Test Strips

These strips are intended for single-use, in vitro diagnosis only. Open the packaging only when ready to use. Ensure they are within their validity period. Prolonged storage (over 1 year) or exposure to moisture, without proper storage at room temperature, can render them ineffective, leading to false negative results. If pregnancy is in its early stages or ectopic (tubal), HCG levels may be low, requiring the sample to rest for over 3 minutes (usually 1 minute suffices) to detect faint positives. After 3 months of pregnancy, HCG levels decline, and urine tests may show negative or weak positive results. In extreme cases like hydatidiform mole or choriocarcinoma, excessively high HCG levels may not register as positive on urine tests. Positive results do not guarantee 100% pregnancy, as certain tumors can also produce HCG. High HCG concentrations (over 50,000 mIU/mL, typically at 2-3 months) may cause hook effects, yielding negative results; dilution is necessary for accurate testing. Positive results in patients with uterine tumors, hydatidiform mole, habitual abortions, threatened abortions, ectopic pregnancies, or menopause should be further evaluated by a doctor.