- As a qualitative analysis of urine levels of human chorionic gonadotropin (hCG), this test can detect pregnancy as early as 14 days after ovulation. A glycoprotein that is produced after conception, hCG prevents degeneration of the corpus luteum at the end of a normal menstrual cycle.
- During the first trimester, hCG levels rise steadily and rapidly, peaking around 10 weeks’ gestation, and subsequently taper off to less than 10% of peak levels. The most common and inexpensive method of evaluating qualitative and quantitative hCG levels is through hemagglutination inhibition of a urine sample. The serum hCG test (beta-subunit assay) is a more expensive alternative.
- To detect and confirm pregnancy.
- To help diagnose hydatiform mole of hCG-secreting tumors, threatened abortion, or dead fetus.
- If appropriate, explain to the patient that the urine hCG test determines whether she’s pregnant or determines the status of her pregnancy.
- Alternatively, explain how the test functions as a screen for some types of cancer.
- Tell the patient that she need not to restrict food but should restrict fluids for 8 hours before the test.
- Inform the patient 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.
- Notify the laboratory and physician of drugs the patient is taking that may affect test results; it may be necessary to restrict them.
- 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 in the appropriate container, discarding the first specimen and retaining the last.
- Specify the date of the patient’s last menstrual period on the laboratory request.
- Refrigerate the 24 hour specimen or keep it on ice during the collection period.
- Be sure the test occurs at least 5 days after a missed period to avoid a false-negative result.
- Instruct the patient to resume her usual diet and medications.
- In a qualitative immunoassay analysis, results are negative (nonpregnant) or positive (pregnant) for hCG.
- In a qualitative 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, from 10,000 to 25,000 IU/24 hours.
- Measurable hCG levels don’t normally appear in the urine of men or nonpregnant women.
- During pregnancy, elevated urine hCG levels may indicate multiple pregnancy or erythoblastosis fetalis; depressed urine hCG levels may indicate threatened abortion or ectopic pregnancy.
- Measurable levels of hCG in men and nonpregnant women may indicate choriocarcinoma, ovarian or testicular tumors, melanoma, multiple myeloma, or gastric, hepatic, pancreatic or breast cancer.
- Gross proteinuria (greater than 1g/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 false-positive).
- Phenothiazine (possible false negative or false positive)
- None known.
image courtesy of: nlm.nih.gov