Human Chorionic Gonadotropin

Etiology and Epidemiology

hCG plays a crucial role in maintaining early pregnancy by supporting the corpus luteum, which in turn sustains progesterone production essential for maintaining the endometrium. The hormone acts through the luteinizing hormone/hCG receptor, activating intracellular signaling pathways that promote steroidogenesis and inhibit luteolysis. Smaller amounts of hCG are also produced in the pituitary gland, the liver, and the colon.[1] 

hCG is a glycoprotein composed of two subunits—the alpha and beta subunits.[1] During pregnancy, multiple forms of the hormone are present in the serum and urine, including both the intact hormone and its free subunits. hCG is primarily catabolized by the liver, although about 20% is excreted in the urine. The beta subunit is degraded into a core fragment in the kidney, which is measured by urine hCG tests.

Pathophysiology

In pathological conditions such as gestational trophoblastic disease—including hydatidiform mole, choriocarcinoma, and germ cell tumors—hCG is produced in excess due to abnormal trophoblastic proliferation, resulting in markedly elevated serum levels. These abnormal elevations can aid in the diagnosis and monitoring of treatment response.

Specimen Requirements and Procedure

Accurate hCG testing begins with proper specimen collection, as errors at this stage can lead to false or misleading results. Adhering to recommended guidelines ensures consistency and improves the reliability of clinical interpretation.

Urine Testing

• Urine should not be collected after the patient drinks a large amount of fluid, as a dilute specimen may result in a falsely negative test.[2]
• Blood in the urine may cause a false-positive result.

Serum Testing

• Peripheral blood can be obtained for a serum hCG test.

Capillary Testing

• There may be a new role for home-based capillary hCG testing, although research on this is still ongoing.[3]

Diagnostic Tests

Serum hCG tests are immunometric assays that use 2 antibodies—a fixed antibody and a radiolabeled antibody, which adhere to different sites on the hCG molecule. These antibodies form a sandwich complex that immobilizes the molecule, allowing for its detection.[4] Assays involve washing away the excess serum components and measuring the amount of remaining labeled hCG to give a quantitative result. More than 100 different assays are commercially available, which results in significant variability in reported values.

Urine assays are similar, although many detect total hCG levels >20 mIU/mL.[5] Many over-the-counter urine pregnancy tests do not detect hyperglycosylated hCG, which accounts for most of the hCG in early pregnancy, resulting in a wide range of sensitivities of these tests.

Serum testing is much more sensitive and specific than urine testing. However, urine testing offers greater convenience, affordability, patient comfort, a rapid turnaround time (typically 5 to 10 minutes), and can be performed without a prescription. As mentioned earlier, capillary testing has recently shown good agreement and strong correlation with venous samples.[3]

Testing Procedures

hCG testing is a crucial diagnostic tool used in both obstetric and oncologic settings. A clear understanding of testing procedures helps ensure accuracy in detecting pregnancy and identifying potential underlying conditions.

Urine Testing

• Urine is placed in or on a designated receptacle, such as those used in most commercially available and medical point-of-care tests.
• If hCG is present, an indicator—typically a colored line or symbol—appears alongside a control line, indicating a positive result.
• If the test is negative, only the control line or symbol is visible.

Serum Testing

• Serum hCG testing is performed in a laboratory equipped with the proper machinery and uses a peripheral blood sample.
• If a hook effect or gestational trophoblastic disease is suspected, the laboratory should perform a dilution before testing.

Interfering Factors

There are multiple reasons why an hCG test—whether serum or urine—may yield a false result. Although rare, false-positive hCG tests can result in unnecessary medical care and irreversible surgical procedures.[6] False-negative results may be equally concerning and result in a delay in care or diagnostic evaluation. Potential causes of false results are outlined below.

False-Positive Serum hCG Results

• Rates of approximately 1 in 1000 to 1 in 10,000 cases
• Ectopic production of hCG can occur in conditions such as hydatidiform mole, choriocarcinoma, and germ cell tumors.[7] Other associated malignancies include multiple myeloma and stomach, liver, lung, bladder, pancreatic, breast, colon, cervical, and endometrial cancers [8][9][10][11][12]
• Heterophile antibodies, including autoantibodies and antibodies formed after exposure to animal products that interact with the assay antibodies [13][14]
• Rheumatoid factors can also bind to the antibodies in the assay
• IgA deficiency [15]
• Chronic renal failure or end-stage renal disease on hemodialysis (rare) [16]
• Red blood cell or plasma transfusion of blood with hCG has been reported
• Exogenous hCG preparations for weight loss, assisted reproduction, and doping [17]

False-Negative Serum hCG Results

• Early measurement after conception 
• The hook effect can occur when hCG levels are about 500,000 mIU/mL.[18] This reading indicates that the abundance of hCG molecules saturates both the tracer and the antibodies separately, preventing the formation of the sandwich of tracer-hCG-antibody required for the measurement. This occurrence means that all the complexes are washed away, resulting in a false-negative result. If gestational trophoblastic disease is suspected, the lab should perform a dilution before testing.

False-Positive Urine hCG Results

• Blood or protein in the urine
• Human error in result interpretation
• Ectopic production of hCG
• Exogenous hCG
• Influence of certain drugs such as aspirin, carbamazepine, and methadone; high urinary pH; and seminal fluid [19]

False-Negative Urine hCG Results

• Early measurement after conception
• Dilute urine specimen [2]
• The hook effect, as discussed above

Results, Reporting, and Critical Findings

hCG levels are reported in milli-international units of hCG hormone per milliliter of blood (mIU/mL). International units per liter (IU/L) may also be used. Serum assays are highly sensitive and can detect beta-hCG levels as low as 1 to 2 mIU/mL.

Urine hCG testing can also be qualitative, reporting a positive or negative result. The assays detect hCG levels typically starting at 20 to 50 mIU/mL, reportedly as low as 6.3 to 12.5 mIU/mL, corresponding to levels approximately 4 weeks post-conception.[20]

Clinical Significance

hCG holds significant clinical value in both reproductive and oncologic medicine. The levels of hCG can provide critical insights into early pregnancy, pregnancy viability, and certain hormone-secreting tumors.

Pregnancy

hCG is a key hormone in pregnancy, and its clinical utility is primarily centered around its detection in early pregnancy, along with serial measurement during pregnancy and pregnancy-related complications.

hCG levels can vary widely among women with normal pregnancies. Typically, serum and urine concentrations of hCG rise exponentially during the first trimester of pregnancy, doubling approximately every 24 hours for the first 8 weeks. The peak typically occurs around 10 weeks of gestation, after which levels decrease until approximately week 16, where they remain relatively constant until term.[4]

Patients whose hCG levels plateau before 8 weeks of gestation or fail to double commonly have a nonviable pregnancy, whether intrauterine or extrauterine. Extrauterine (ectopic) pregnancies typically exhibit a low rate of rise without the expected doubling. However, given the wide range of normal hCG levels and the variability in its rate of rise, serum hCG testing is often combined with ultrasound evaluation to improve sensitivity and specificity.[21] 

A threshold of 5000 IU/L has been associated with the need for surgical intervention (>5000 IU/L) versus successful medical intervention (<5000 IU/L).[22][23] In addition, there has been recent discussion that elevated beta-hCG levels in the second trimester may be associated with adverse pregnancy outcomes and should prompt further investigation.[24]

The return of hCG to zero following delivery or termination of pregnancy typically takes between 7 and 60 days.[25] Monitoring the decline in hCG levels is crucial in terminating molar pregnancies and also following the termination of normal or ectopic pregnancies to assure that the therapy has been successful.

Notably, many different combinations of antibodies are used in commercial assays. This variety yields heterogeneous results, with a 50-fold difference in immunoassay results.[4] This potential disparity is clinically relevant, particularly when comparing results from different laboratories in different facilities or hospitals when examining low values following pregnancy termination or trophoblastic disease.

Gestational Trophoblastic Disease

Detection of hCG is also helpful in evaluating trophoblastic disease, including complete and partial hydatidiform moles, postmolar tumors, gestational choriocarcinoma, testicular choriocarcinoma, and placental site trophoblastic disease. All these entities produce hCG, varying levels of which are reported on commercial assays. For example, a total hCG level >100,000 mIU/mL in early pregnancy is highly suggestive of a complete hydatidiform mole, although many normal pregnancies may reach this level at their peak around weeks 8 to 11 of gestation.[26] Precise hCG measurements are crucial for assessing the tumor mass, determining the success of malignancy treatment, and detecting disease recurrence or persistence.[7]

Nonpregnant Patients

hCG in the serum increases with age in nonpregnant women. A cutoff value of 14 mIU/mL has been suggested for use in interpreting results in women older than 55. In all nonpregnant patients, testicular cancer, ovarian cancer, bladder cancer, neuroendocrine tumors, or other malignancies should be considered as potential sources of positive hCG results.[27] hCG levels can also help determine prognosis in these cases, with higher levels associated with a poor prognosis in testicular cancers.[28]

Quality Control and Lab Safety

Quality control and laboratory safety are integral to the accuracy and reliability of hCG testing. The routine use of control materials is crucial for monitoring assay performance, identifying analytical errors, and ensuring the consistency of results. Strict adherence to biosafety protocols, proper specimen handling, and regular maintenance of instrumentation are critical for minimizing contamination risks and maintaining a safe working environment. Furthermore, compliance with established laboratory standards and regulatory guidelines supports diagnostic accuracy and improves clinical outcomes.

Enhancing Healthcare Team Outcomes

Effective patient-centered care involving hCG testing and interpretation requires a collaborative, multidisciplinary approach grounded in strong clinical skills, strategic planning, ethical integrity, and seamless communication. Clinicians and advanced practitioners must possess the diagnostic acumen to interpret hCG levels within the appropriate clinical context, whether to confirm pregnancy, monitor gestational complications, or identify malignancies. Nurses play a vital role in specimen collection, patient education, and emotional support, ensuring patients understand the purpose and implications of hCG testing. Pharmacists contribute by evaluating the potential effects of medications on hCG levels and supporting informed therapeutic decisions.

Understanding the utility and variability of different hCG assays is clinically relevant to a wide range of medical professionals. False-positive and false-negative testing have a large impact on patient care. All members of the healthcare team should be aware of common limitations in testing, such as urine assay false positives with hematuria, false negatives with dilute urine, and more obscure but still very relevant causes of inaccurate testing. Interpreting results that may be false should be undertaken with care to help prevent unnecessary testing and treatment.[29] 

Effective interprofessional communication is crucial for making timely clinical decisions, enabling all team members to collaborate in sharing relevant findings and coordinating follow-up care. Coordinated care ensures that abnormal results are promptly addressed, referrals are efficiently managed, and patients receive accurate information and support throughout their diagnostic journey. By aligning their roles and responsibilities, healthcare professionals can enhance patient safety, improve clinical outcomes, elevate team performance, and foster a high-performing, patient-centered care environment.