Human chorionic gonadotropin (hCG)

        

Function

 

Human chorionic gonadotropin (hCG) is a glycoprotien hormone secreted by the developing placenta shortly after implantation.

         Measuring hCG levels can be helpful in identifying a normal pregnancy, pathologic pregnancy, and can also be useful following an aborted pregnancy. There is also a benefit in measuring hCG in a variety of cancers including choriocarcinoma and extra-uterine malignancies

        Smaller amounts of hCG are also produced in the pituitary gland, the liver, and the colon. As previously mentioned, certain malignancies can also produce either hCG or hCG-related hormone.

       

  The hormone itself is a glycoprotein composed of two subunits, the alpha and beta subunits. There are multiple forms found in the serum and urine during pregnancy including the intact hormone and each of the free subunits. HCG is primarily catabolized by the liver, although about 20% is excreted in the urine. The beta subunit is degraded in the kidney to make a core fragment which is measured by urine hCG tests.

    Testing

Urine Testing

• Urine should not be collected after the patient has been drinking a large amount of fluid, as a dilute specimen may result in a falsely negative test.
• Blood in the urine may cause a false positive test result.

Serum Testing

• Peripheral blood can be obtained for a serum hCG test

Serum testing is much more sensitive and specific than urine testing. Urine testing, however, is more convenient, affordable, comfortable for patients, has a fast turnaround (5 to 10 minutes), and does not require a medical prescription.

Test Procedure

Human chorionic gonadotropin (hCG) : Rapid Quantitative test is a fluorescence immunoasssy used along with Finecare FIA System.

Material Provided:

-Test Cartridge in a sealed pouch with desiccant

-ID Chip

-Detection Buffer

    Step 1: Insert ID chip into Finecare FIA System

    Step 2: Draw 20ul of serum or plasma and add into the Detection Buffer

    Step 3: Mixing Detection Buffer's sample about 10 times.

    Step 4:Pipette 75ul of sample mixture and load it into the sample well of the test Cartridge

    Step 5: There are two test modes

                For Standard test mode : Insert the test the holder of Finecare and then press test.

                For Quick test mode     : Set the timer and count down 15 minutes out side it is for many tests 

 

    

 Interfering Factors

There are multiple reasons why an hCG test (serum or urine) may have a false report. While uncommon, false positive hCG tests can result in unnecessary medical care and/or irreversible surgical procedures. False negatives may be equally concerning and result in a delay in care or diagnostic evaluation. Potential causes of false results are listed and briefly discussed.

Serum False Positives (1/1000 to 1/10,000)

• Ectopic production of hCG (hydatidiform mole, choriocarcinoma, and germ cell tumors, in addition to multiple myeloma, stomach, liver, lung, bladder, pancreatic, breast, colon, cervical, and endometrial cancers)
• Heterophile antibodies (autoantibodies and antibodies formed after exposure to animal products that interact with the assay antibodies)
• Rheumatoid factors (can bind the antibodies in the assay as well)
• IgA deficiency
• Chronic renal failure or ESRD on hemodialysis (rare)
• Red blood cell or plasma transfusion of blood with hCG in it have been reported
• Exogenous hCG preparations for weight loss, assisted reproduction, doping

Serum False Negatives

• Early measurement after conception 
• "Hook effect" can occur when hCG levels are about 500,000 mIU/mL.This is because there are so many hCG molecules that they saturate both the tracer and the antibodies separately, which doesn't allow for the sandwiching of the tracer-hCG-antibody required for the measurement. This means that all of the complexes are washed away, giving a false-negative result. If gestational trophoblastic disease is suspected, the lab should perform a dilution prior to testing.

Urine False Positives

• Blood or protein in the urine
• Human error in result interpretation
• Ectopic production of hCG
• Exogenous hCG
• Drugs (aspirin, carbamazepine, methadone, high urinary pH and seminal fluid)

Urine False Negatives

• Early measurement after conception
• Dilute urine specimen
• "Hook effect" as discussed above

Levels of hCG can vary widely between women with normal pregnancies. Typically, serum and urine concentrations of hCG rise exponentially in the first trimester of pregnancy, doubling about every 24 hours during the first 8 weeks. The peak is usually around 10 weeks of gestation and then levels decrease until about the 16th week of gestation where they remain fairly constant until term.

     

     Return of hCG to zero following delivery or termination of pregnancy ranges from 7 to 60 days.Trending the fall of hCG levels can be important in termination of molar pregnancies and also following the termination of normal or ectopic pregnancies to be assured that the therapy has been successful

  

     Non-Pregnant Patients

HCG in the serum increases with age in nonpregnant women. A cut off of 14 mIU/mL has been suggested for use in interpreting results in women over the age of 55. In all nonpregnant patients, testicular cancer, ovarian cancer, bladder cancer, or other malignancy should be evaluated as a source of persistently positive hCG testing

    Gestational Trophoblastic Disease

is a group of rare diseases in which abnormal trophoblast cells grow inside the uterus after conception(the joining of sperm and egg).

Detection of hCG is also useful in the evaluation of trophoblastic disease, including complete and partial hydatidiform mole, postmolar tumor, gestational choriocarcinoma, testicular choriocarcinoma, and placental site trophoblastic disease. All of these entities produce hCG, varying levels of which are reported on commercial assays. A total hCG level of greater than 100,000 mIU/mL in early pregnancy, for example, 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. Precise hCG measurements are important to assess the tumor mass, the successful treatment of malignancy, and to test for recurrence or persistence of disease

Weeks of Pregnancy	Range mUI/ml
3 4 5 6 7 8 9 10 12 14 15 16 17 18 <5	5.8-71.2 9.5-750 217-7138 158-31,795 3697-163,563 32,065-149,571 63,803-151,410 46,509-186,977 27,832-210,612 13,950-62,530 12,093-70,971 9040-56,451 8175-55,868 8099-58176 Non-Pregnacy

References

https://www.ncbi.nlm.nih.gov/books/NBK532950/

https://en.wikipedia.org/wiki/Human_chorionic_gonadotropin