Obstetrics Book

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Pregnancy TestAka: Beta hCG, Quantitative hCG, Quantitative bhCG, Qualitative hCG, bhCG

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  1. Indications
    1. Pregnancy diagnosis and monitoring
    2. Tumor monitoring
      1. Nonseminomatous germ cell tumor monitoring
      2. Hydatiform mole diagnosis and monitoring
      3. Choriocarcinoma diagnosis and monitoring
  2. Physiology
    1. HCG is a glycoprotein hormone with subunits a and b
      1. Composed of 65% polypeptides by molecular weight
      2. Composed of 35% large sugar side chains (8 chains)
        1. Four are N-Linked (2 each on alpha and beta)
        2. Four are O-Linked (all 4 are on beta subunit)
      3. Forms of HCG found in blood and urine
        1. Intact HCG with alpha and beta subunits
        2. Nicked HCG and nicked free beta subunit
        3. Free beta subunit and free alpha subunit
        4. Hyperglycosylated free beta and free alpha subunits
        5. Beta core fragment (present only in urine)
    2. HCG shares the same alpha subunit with other hormones
      1. Luteinizing hormone (LH)
      2. Thyroid Stimulating Hormone (TSH)
    3. Urine and Blood HCG tests are specific for beta subunit
    4. Serum half life of HCG: 24 to 36 hours
  3. Interpretation: Levels of bHCG in pregnancy
    1. Estimation in normal pregnancy for weeks 4 to 8
      1. Anticipate HCG doubling every 48 to 72 hours
    2. Chart of corresponding gestational age
      1. Day 23 (3.3 weeks): 100 mIU/ml
      2. Day 28 (4.0 weeks): 250 mIU/ml
      3. Day 35 (5.0 weeks): 1000 mIU/ml
        1. bHCG 1800: Gestational Sac on Transvaginal U/S
        2. bHCG 3500: Gestational Sac on Transabdominal U/S
      4. Day 42 (6.0 weeks): 4000 mIU/ml
      5. Day 49 (7.0 weeks): 15000 mIU/ml
        1. bHCG 20,000: 5-10 mm Embryo with cardiac activity
      6. Day 56 (8.0 weeks): 65000 mIU/ml
      7. Decreases gradually after 8 weeks
      8. Plateaus after 20 weeks
    3. Ranges of bHCG over each Trimester
      1. First Trimester: 30,000 to 100,000 mIU/ml
      2. Second Trimester: 10,000 to 30,000 mIU/ml
      3. Third Trimester: 5,000 to 15,000 mIU/ml
  4. Efficacy: Home pregnancy tests
    1. Variable efficacy after missed Menses
      1. Wide discrepancy between brands
      2. Cole (2004) Am J Obstet Gynecol 190:100
  5. Causes: Elevated bHCG in non-pregnant state
    1. HCG-producing tumors in women
      1. Hydatidiform Mole or Choriocarcinoma
    2. HCG-producing tumors in men
      1. HCG is usually undetectable in healthy males
      2. Nonseminomatous germ cell tumor (Testicular Cancer)
        1. Used with AFP for monitoring
  6. Causes: False positive increased serum hCG
    1. Causes
      1. Heterophilic Antibody (most common)
      2. Human anti-mouse Antibody (HAMA)
      3. Nonspecific protein-binding hCG-like substances
      4. Red Blood Cell interference
      5. Marijuana use
      6. Hypogonadism
    2. Confirmation methods in non-pregnant conditions
      1. Qualitative urine hCG
      2. Serum hCG by different immunoassay method
      3. Serial dilutions of serum hCG sample
  7. HCG in Nonseminomatous germ cell tumor (Men)
    1. Interpretation
      1. Poor prognosis if bHCG >50,000 mIU/ml at diagnosis
      2. Five year survival rate: 50%
    2. Efficacy
      1. High Specificity in men
      2. Low Test Sensitivity
        1. HCG or AFP increased in 85% of patients
        2. HCG or AFP increased in only 20% of Stage 1 Cancer
    3. Protocol
      1. Initial: bHCG with AFP q1-2 months for 1 year
      2. Later: bHCG with AFP q3 months for 1 year
  8. References
    1. Bakerman, ABCs Interpretive Lab Data, p. 239-40
    2. (1997) J Clin Oncol 15:594
    3. Hay (1988) J Clin Endocrinol Metab 67:1322

Pregnancy Tests (C0032976)

Definition (MSH)Tests to determine whether or not an individual is pregnant.
Definition (CSP)determining whether or not a female is pregnant.
ConceptsDiagnostic Procedure (T060)
EnglishPREGN TEST, PREGN TESTS, Pregnancy detection examination, Pregnancy Test, Pregnancy Tests, TEST PREGN, TESTS PREGN
Spanishexamen de detección del embarazo, examen de deteccion del embarazo
CreditsDerived from the NIH UMLS (Unified Medical Language System)


Chorionic Gonadotropin, beta Subunit, Human (C0106132)

Definition (MSH)The beta subunit of human CHORIONIC GONADOTROPIN. Its structure is similar to the beta subunit of LUTEINIZING HORMONE, except for the additional 30 amino acids at the carboxy end with the associated carbohydrate residues. HCG-beta is used as a diagnostic marker for early detection of pregnancy, spontaneous abortion (ABORTION, SPONTANEOUS); ECTOPIC PREGNANCY; HYDATIDIFORM MOLE; CHORIOCARCINOMA; or DOWN SYNDROME.
Definition (NCI)Contiguous with the LH beta subunit gene on chromosome 19q13.3, six homologous genes arranged in tandem and inverted pairs encode the beta subunit of Chorionic Gonadotropin (Glycoprotein Hormone Beta Family).Glycoprotein hormones are heterodimers of a common alpha subunit and a unique beta subunit that confers biological specificity. Produced by placental trophoblasts, Chorionic Gonadotropin stimulates ovarian steroid synthesis essential for maintenance of pregnancy. (NCI)
Definition (NCI)Human chorionic gonadotropin is a glycoprotein hormone produced by placental trophoblasts 10-12 days after conception and during the first trimester. HCG binds to the corpus luteum to stimulate progesterone production, which maintains the secretory endometrium and the fetus. HCG is a heterodimer of a common alpha chain and a unique beta chain that confers biological specificity to thyrotropin, lutropin, follitropin and gonadotropin. (from OMIM 118860, SWISS-PROT P01233, and NCI)
ConceptsAmino Acid, Peptide, or Protein (T116) , Hormone (T125)
EnglishBeta human chorionic gonadotrophin, CGB3, Choriogonadotropin Beta Chain, Chorionic Gonadotrophin Beta Subunit, Chorionic Gonadotropin Beta 3 Subunit, Chorionic Gonadotropin Beta Chain, Chorionic Gonadotropin Beta Polypeptide, CHORIONIC GONADOTROPIN BETA SUBUNIT HUMAN, HCG beta, hCGBeta, Human Chorionic Gonadotropin Beta Subunit
CreditsDerived from the NIH UMLS (Unified Medical Language System)



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