Human Chorionic Gonadotropin (hCG) Pregnancy Test

Definition
  • 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.
Purpose
  • To detect and confirm pregnancy.
  • To help diagnose hydatiform mole of hCG-secreting tumors, threatened abortion, or dead fetus.
Procedure
Patient Preparation
  1. If appropriate, explain to the patient that the urine hCG test determines whether she’s pregnant or determines the status of her pregnancy.
  2. Alternatively, explain how the test functions as a screen for some types of cancer.
  3. Tell the patient that she need not to restrict food but should restrict fluids for 8 hours before the test.
  4. 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.
  5. Notify the laboratory and physician of drugs the patient is taking that may affect test results; it may be necessary to restrict them.
Implementation
  1. For verification of pregnancy (qualitative analysis), collect a first-voided morning specimen. If this isn’t possible, collect a random specimen.
  2. 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.
  3. Specify the date of the patient’s last menstrual period on the laboratory request.
  4. Refrigerate the 24 hour specimen or keep it on ice during the collection period.
  5. Be sure the test occurs at least 5 days after a missed period to avoid a false-negative result.
Nursing Interventions
  1. Instruct the patient to resume her usual diet and medications.
Interpretation
Normal Results
  • 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.
Abnormal Results
  • 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.
Interfering Factors
  • 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)
Complication
  • None known.

 

 

image courtesy of: nlm.nih.gov

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