Why does the patient (pt) continue to test positive for pregnancy at home, but have a negative human chorionic gonadotropin (hCG) qualitative test in the clinic?

From the Guidelines

The patient's positive home pregnancy tests but negative qualitative hCG tests in the clinic are likely due to the high sensitivity of home tests, which can detect very low levels of hCG, or a recent pregnancy loss, where hCG levels are declining but still detectable on home tests. According to the U.S. selected practice recommendations for contraceptive use, 2013, the sensitivity of a pregnancy test is defined as the concentration of human chorionic gonadotropin (hCG) at which 95% of tests are positive, and most qualitative pregnancy tests approved by the U.S. Food and Drug Administration (FDA) report a sensitivity of 20–25 mIU/mL in urine 1. This discrepancy in sensitivity between home tests and clinical qualitative tests can lead to false positives at home.

Some possible explanations for this discrepancy include:

• Very early pregnancy, where hCG levels are just beginning to rise
• Recent miscarriage or chemical pregnancy, where hCG levels are declining but still detectable on home tests
• Technical factors such as improper use of home tests, expired tests, or certain medications containing hCG
• Certain medical conditions like ovarian cysts, gestational trophoblastic disease, or rare tumors that can produce low levels of hCG

The patient's situation can be evaluated using the criteria listed in the U.S. selected practice recommendations for contraceptive use, 2013, which include assessing symptoms and signs of pregnancy, recent sexual intercourse, and recent pregnancy 1. A quantitative serum hCG test should be considered to provide an exact measurement of hCG levels and determine if levels are rising, falling, or stable. This will help to confirm or rule out pregnancy and guide further management. Additionally, the patient's contraceptive needs should be assessed, and the benefits and risks of starting contraceptive methods should be discussed, taking into account the uncertainty of the patient's pregnancy status 1.

From the Research

Possible Causes of Discrepancy

• The patient may be experiencing an ectopic pregnancy, where the embryo implants outside the uterus, leading to abnormal hCG levels 2, 3.
• The patient may be having a miscarriage or an abnormal intrauterine pregnancy, which can cause hCG levels to be lower than expected 4.
• The timing of the hCG test may be too early, before the hCG levels have risen to detectable levels 5, 6.
• The sensitivity of the home pregnancy test may be higher than the clinic's hCG qualitative test, leading to false positives at home 3.
• The presence of heterophilic antibodies or other substances in the patient's urine or blood may be causing false-positive results on the home pregnancy test 3.

Diagnostic Considerations

• A quantitative beta-hCG test may be necessary to determine the exact level of hCG in the patient's blood, which can help diagnose ectopic pregnancy or other complications 2, 5.
• Transvaginal ultrasound may be used to visualize the embryo and determine if it is implanted in the uterus or elsewhere 2, 5, 6.
• Progesterone levels may also be measured to help differentiate between normal and abnormal pregnancies 4.
• The patient's symptoms, medical history, and physical examination should be taken into account when interpreting the test results and making a diagnosis 2, 3.