Pregnancy tests detect a specific hormone that signals a developing pregnancy. While a positive result usually indicates conception, in rare instances, other medical conditions can also lead to a positive test result.
How Pregnancy Tests Detect hCG
Pregnancy tests identify Human Chorionic Gonadotropin (hCG), often called the “pregnancy hormone.” It is primarily produced by placental cells that nourish a developing embryo after implantation. Both home urine and blood tests detect hCG. After conception, hCG levels rise rapidly, approximately doubling every 36 to 48 hours, and typically peak around 8 to 11 weeks of pregnancy.
Non-Cancerous Reasons for a Positive Test
While pregnancy is the most common reason for a positive test, several non-cancerous factors can also lead to this result. One such scenario is a chemical pregnancy, which occurs when a fertilized egg implants but fails to develop into a viable pregnancy. In these cases, hCG is produced briefly before the pregnancy ends very early. A recent pregnancy loss, such as a miscarriage, abortion, or even childbirth, can also cause a positive test. hCG levels can remain elevated for several days to weeks (typically 9 to 35 days) after the pregnancy ends, leading to a positive result. Certain fertility treatments, particularly those involving hCG injections to stimulate ovulation, can also result in a temporary positive test. Less commonly, user error, such as reading the test outside the recommended timeframe or using an expired test, can produce a false positive.
Cancers That Can Cause a Positive Test
Although rare, certain cancers can produce hCG, leading to a positive pregnancy test. This occurs because some cancerous cells can mimic placental cells that typically produce this hormone. A primary example is Gestational Trophoblastic Disease (GTD), a group of conditions that arise from placental cells, including hydatidiform mole and choriocarcinoma. These conditions are directly related to pregnancy tissues and produce significant levels of hCG. Beyond GTD, germ cell tumors, which can develop in the ovaries or testes, are also known to produce hCG. In men, a positive pregnancy test has led to the diagnosis of testicular cancer. In rare instances, other cancers, such as those of the lung, breast, bladder, kidney, liver, colon, or stomach, may also produce hCG. However, these occurrences are less common than hCG production by GTD or germ cell tumors.
When to Seek Medical Advice
If a pregnancy test shows a positive result but a confirmed pregnancy is not expected, consult a healthcare professional. A doctor can perform more accurate blood tests to measure the exact amount of hCG in the blood, which provides more detailed information than a urine test. These quantitative blood tests can help determine if hCG levels are rising as expected in a viable pregnancy or if they indicate another condition. Depending on hCG levels and other clinical signs, further diagnostic steps, such as ultrasounds or specialized tests, may be necessary to investigate the underlying cause. Medical evaluation is crucial for an accurate diagnosis and appropriate management, ensuring any underlying medical conditions are identified and addressed promptly.