Pregnancy Test

• Pregnancy test are based on the detection of the human chorionic gonadotropin or hcg
• Human Chorionic Gonadotropin (hCG) is produced by the placenta during pregnancy.
• Human chorionic gonadotropin is produced by the placenta shortly after fertilization and reaches detectable levels in urine and serum about 1 week after implantation attachment of the early embryo to the uterine lining
• The levels continue to rise during the first trimester of pregnancy,making it an excellent marker of pregnancy
• Alpha-subunit is common with other hormones like LH and FSH
• Beta-subunit is specific for HCG
• Follicle Stimulating Hormone (FSH): Beta subunit has 30 amino acids
• Luteinizing Hormone (LH): Beta subunit has 24 amino acids
• Most pregnancy tests used today, whether a home urine test, a physician's office urine or blood test, or a clinical laboratory blood test are "sandwich assays"
• Sandwich assays use two or more animal antibodies raised against different sites on Human Chorionic Gonadotropin (hCG).
• Usually a mouse monoclonal antibody against one site on the hCG molecule, and a mouse monoclonal, or a sheep, rabbit or a goat polyclonal antibody against a second distant site on the hCG molecule.
• Can be done in blood and urine sample, either can detect hCG
• First morning may contain highest hCG but any time collected maybe used
• Urine is preferred because it contains higher concentration of hCG than serum
• Usually, concentration of hCG in urine is at least 25 mIU/ml as early as seven to ten days after conception.
• The concentration increases steadily and reaches its maximum between the eighth and eleventh weeks of pregnancy
• One antibody, the capture antibody, is in a solid phase permanently attached to a tube, plate, membrane, or bead.
• Conjugate pad contains the label reagent, i.e. antibody labeled with either red, gold or blue latex particles.
• Sample is applied and dissolves the label mixture and migrates to the zone of immobilized antibody lines. If hCG is present, labeled antibody-dye conjugate binds it, forming an antibody-antigen complex.
• Positive, that is hCG containing, sample causes the formation of a colored test line, which indicates a positive test result.
• The test uses two lines to indicate results, this test is done by immersing the test strip in a urine or serum specimen and observing the formation of colored lines.
• The specimen migrates via capillary action along the membrane to react with the colored conjugate
• A second line appears if hCG is present, indicating a positive pregnancy test result.
• The Control Band is used as a reference and built in quality control check. If the Test Band is darker or similar to the Control band, the test result is considered positive.
• If a color appears in the test area but NO color appears in the control area, the test is invalid.
• If no color appears in either the test area or the control area, the test is negative.
• Causes of invalid results:

  • The directions may not have been followed correctly.
  • Inadequate amount of sample has been exposed to the test system.
  • The test may have deteriorated.
• Limitations of the procedure:

  1. High hCG levels can indicate pregnancy or trophoblastic diseases.
  2. Consult a doctor for unexpected or inconsistent results.
  3. hCG levels alone can't distinguish between a normal and ectopic pregnancy.
  4. Miscarriage can complicate test result interpretation.
  5. Diagnosis relies on comprehensive evaluation, not just one test.
  6. Low hCG levels in early pregnancy may lead to false negatives; repeat the test.
  7. Diluted urine may affect results; use a first morning urine sample if needed.
• Advantage of using a blood test:

  • Can detect pregnancy earlier than a urine testat about 3-10 days from possible conception
  • Can measure the concentration of hCG hormone in your blood , helpful to he clinician in case there are probles in pregnancy
• Disadvantage using blood:

  • More expensive than Urine test
  • Takes longer to release the result
  • Must be done in a clinical laboratory
• High levels of Beta hCG are seen in case there is:

  An error in calculation of pregnancy date

  Abnormal pregnancy

  More than 1 pregnancy

  Germ cell tumor

  Gestational trophoblastic disease
• Low levels of beta hCG are seen in case of:

  An error in calculation of pregnancy date

  Miscarriage

  Pregnancy without embryo

  Pregnancy outside the uterus other than normal location
• Ectopic Pregnancy - This unfortunate patient came in with a late cycle. The pregnancy test was positive but we couldn't see a pregnancy on her ultrasound scan.
• Choriocarcinoma is a dangerous tumor linked to abnormal pregnancies like hydatidiform moles, sometimes after miscarriages, and rarely after normal pregnancies. It spreads quickly through blood vessels.
• An ectopic pregnancy is when a fertilised egg implants itself outside of the womb, usually in one of the fallopian tubes.
• Hydatidiform mole is a placenta tumor usually harmless, forming when a pregnancy fails to develop properly. It looks like a cluster of grapes. While rare in the USA, it's more common in the Orient and elsewhere. In the US, it happens in about 1 out of every 1,000-1,200 pregnancies.
• Seminoma

  50% of all testicular tumors.

  Human chorionic gonadotropin-beta is a better marker than hCG.

  For earlier detection of recurrence, both markers should be examined.