Human Chorionic Gonadotropin

Qualitative analysis of urine levels of human chorionic gonadotropin (hCG) allows for detection of pregnancy as early as 10 days after a missed menstrual period. Production of hCG, a glycoprotein, which prevents degeneration of the corpus luteum at the end of the normal menstrual cycle, begins after conception. During the first trimester, hCG levels rise steadily and rapidly, peaking around the 10th week of gestation, subsequently tapering off to less than 10% of peak levels.

The most common method of evaluating hCG in urine is hemagglutination inhibition. This laboratory procedure can provide both qualitative and quantitative information. The qualitative urine test is easier and less expensive than the serum hCG test (beta-subunit assay); therefore, it's used more frequently to detect pregnancy.

Purpose

• To detect and confirm pregnancy
• To aid diagnosis of hydatidiform mole or hCG-secreting tumors

Patient preparation

• If appropriate, explain to the patient that this test determines whether she is pregnant or the status of her pregnancy. Alternatively, explain how the test functions as a screen for some types of cancer.
• Tell her she needn't restrict food or fluids before the test.
• Inform her that the test requires a first-voided morning specimen or urine collection over a 24-hour period, depending on whether the test is qualitative or quantitative.

Procedure and posttest care

• For verification of pregnancy (qualitative analysis), collect a first-voided morning specimen. If this isn't possible, collect a random specimen.
• For quantitative analysis of hCG, collect the patient's urine over a 24-hour period.
• Specify the date of the patient's last menstrual period on the laboratory slip.
• Resume administration of medications withheld during the test.

Precautions

• Refrigerate the 24-hour specimen or keep it on ice during the collection period.

Reference values

In quantitative analysis, urine hCG levels in the first trimester of a normal pregnancy may be as high as 500,000 IU/24 hours; in the second trimester, they range from 10,000 to 25,000 IU/24 hours; and in the third trimester, from 5,000 to 15,000 IU/ 24 hours.

Measurable hCG levels don't normally appear in the urine of men or non-pregnant women.

Abnormal findings

During pregnancy, elevated urine hCG levels may indicate multiple pregnancy or erythroblastosis fetalis; depressed urine hCG levels may indicate threatened abortion or ectopic pregnancy.

Measurable levels of hCG in males and nonpregnant females may indicate choriocarcinoma, ovarian or testicular tumors, melanoma, multiple myeloma, or gastric, hepatic, pancreatic, or breast cancer.

Interfering factors

• Failure to properly store the specimen during the collection period
• Gross proteinuria (> 1 g/24 hours), hematuria, or an elevated erythrocyte sedimentation rate (possible false-positive, depending on the laboratory method)
• Early pregnancy, ectopic pregnancy, or threatened abortion (possible false­negative)
• Phenothiazine (possible false-negative or false-positive)
• Injection of hCG to treat infertility (possible false-positive)