Test ID: THCG
Human Chorionic Gonadotropin (hCG), Quantitative, Pregnancy, Serum
Secondary ID 
A test code used for billing and in test definitions created prior to November 2011
NY State Approved Indicates the status of NY State approval and if the test is orderable for NY State clients.
Useful For Suggests clinical disorders or settings where the test may be helpful
Diagnosing pregnancy
Investigation of suspected ectopic pregnancy
Monitoring in vitro fertilization patients
Method Name A short description of the method used to perform the test
Electrochemiluminescent Immunoassay
Reporting Name A shorter/abbreviated version of the Published Name for a test; an abbreviated test name
Aliases Lists additional common names for a test, as an aid in searching
CG (Chorionic Gonadotropin)
HCG Total OB
HCGB (Human Chorionic Gonadotropin Beta Subunit)
Pregnancy Test
Total Chorionic Gonadotropin
Human Chorionic Gonadotropins (hCG)
HCG (Human Chorionic Gonadotropins)
Gonadotropins, Chorionic
Specimen Type Describes the specimen type needed for testing
Specimen Required Defines the optimal specimen. This field describes the type of specimen required to perform the test and the preferred volume to complete testing. The volume allows automated processing, fastest throughput and, when indicated, repeat or reflex testing.
Container/Tube:
Preferred: Serum gel
Acceptable: Red top
Specimen Volume: 0.5 mL
Additional Information: For use as a tumor marker (eg, testicular cancer patients), see BHCG/61718 Beta-Human Chorionic Gonadotropin, Quantitative, Serum.
Specimen Minimum Volume Defines the amount of specimen required to perform an assay once, including instrument and container dead space. Submitting the minimum specimen volume makes it impossible to repeat the test or perform confirmatory or perform reflex testing. In some situations, a minimum specimen volume may result in a QNS (quantity not sufficient) result, requiring a second specimen to be collected.
Reject Due To Identifies specimen types and conditions that may cause the specimen to be rejected
| Hemolysis | Mild OK; Gross reject |
| Lipemia | NA |
| Icterus | NA |
| Other | NA |
Specimen Stability Information Provides a description of the temperatures required to transport a specimen to the laboratory. Alternate acceptable temperature(s) are also included.
| Specimen Type | Temperature | Time |
|---|---|---|
| Serum | Refrigerated (preferred) | 72 hours |
| Frozen | 365 days |
Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
Human chorionic gonadotropin (hCG) is a glycoprotein with 2 noncovalently bound subunits. The alpha subunit is similar to those of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). The beta subunit of hCG differs from other pituitary glycoprotein hormones, which results in its unique biochemical and immunological properties.
hCG is synthesized by the cells of the placenta and is involved in maintaining the corpus luteum during pregnancy. It is detected as early as 1 week after conception. The diagnostic cutoff for pregnancy is >25 IU/L. In pregnancy, the levels of hCG increase exponentially for about 8 to 10 weeks after the last menstrual cycle. Later in pregnancy, about 12 weeks after conception, the concentration of hCG begins to fall.
Other sources of elevated hCG values include ectopic pregnancy, threatened abortion, microabortion, recent termination of pregnancy, gestational trophoblastic disease, choriocarcinoma, and some germ cell tumors.
Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
Negative: <5 IU/L
Indeterminate: 5-25 IU/L
Positive: >25 IU/L
Suggest repeat testing of indeterminate results in 72 hours.
Interpretation Provides information to assist in interpretation of the test results
Values between 5 and 25 IU/L are indeterminate for pregnancy. Consider confirming with repeat test in 72 hours. Values in pregnancy should double every 3 days for the first 6 weeks.
Both normal and ectopic pregnancies generally yield positive results of pregnancy tests. The comparison of quantitative human chorionic gonadotropin (hCG) measurements with the results of transvaginal ultrasonography (TVUS) may aid in the diagnosis of ectopic pregnancy. When an embryo is first large enough for the gestation sac to be visible on TVUS, the patient generally will have hCG concentrations between 1,000 and 2,000 IU/L. (These are literature values. Definitive values for this method have not been established at this time.) If the hCG value is this high and no sac is visible in the uterus, ectopic pregnancy is suggested. Elevated values will also be seen with choriocarcinoma and hydatiform mole.
Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
False-elevations (called phantom human chorionic gonadotropin [hCG]) may occur with patients who have human antianimal or heterophilic antibodies.
Some specimens may not dilute linearly due to abnormal forms of hCG.
Some patients who have been exposed to animal antigens, either in the environment or as part of treatment or an imaging procedure, may have circulating antianimal antibodies present. These antibodies may interfere with the assay reagents to produce unreliable results.
Clinical Reference Provides recommendations for further in-depth reading of a clinical nature
Snyder JA, Haymond S, Parvin CA, et al: Diagnostic considerations in the measurement of human chorionic gonadotropin in aging women. Clin Chem 2005;51:1830-1835
Method Description Describes how the test is performed and provides a method-specific reference
The Roche E Modular HCG+B method employs 2 monoclonal antibodies specifically directed against huamn chorionic gonadotropin (hCG). A biotinylated monoclonal antibody and a second monoclonal antibody labeled with a ruthenium complex react with hCG to form a sandwich complex. After the addition of streptavidin-coated microparticles, the complex becomes bound to the solid phase via interaction of biotin and streptavidin. The reaction mixture is aspirated into the measuring cell where the microparticles are magnetically captured onto the surface of the electrode. Application of a voltage to the electrode then induces chemiluminescent emission, which is measured by a photomultiplier. (Package insert: HCG+B, Roche Diagnostics Corporation, Indianapolis IN).
Day(s) and Time(s) Test Performed Outlines the days and times the test is performed. This field reflects the day and time the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time required before the test is performed. Some tests are listed as continuously performed, which means assays are performed several times during the day.
Monday through Sunday; Continuously
Analytic Time Defines the amount of time it takes the laboratory to setup and perform the test. This is defined in number of days. The shortest interval of time expressed is "same day/1 day," which means the results may be available the same day that the sample is received in the testing laboratory. One day means results are available 1 day after the sample is received in the laboratory.
Maximum Laboratory Time Defines the maximum time from specimen receipt at Mayo Medical Laboratories until the release of the test result
Specimen Retention Time Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location The location of the laboratory that performs the test
Test Classification Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer's instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR), Investigation Use Only (IUO) product, or a Research Use Only (RUO) product.
CPT Code Information Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Medical Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
84702
LOINC® Code Information Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the result codes returned for this test or profile.
| Result ID | Reporting Name | LOINC Code |
|---|---|---|
| THCG | HCG, Quantitative, Pregnancy, S | 21198-7 |
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