AUBF Pregnancy Test

• Human Chorionic Gonadotropin (HCG) is a glycoprotein hormone with two sub-units: Alpha sub-unit, which is similar to LH, FSH, and TSH, and Beta sub-unit, which is unique for HCG.
• Toxic Urine sample can be caused by excess electrolytes, particularly potassium.
• Bacterial contamination or toxic substances can also cause a Toxic Urine sample.
• Salicylates and barbiturates reaction can lead to a False Negative Interference in a Toxic Urine sample.
• The main function of HCG is for the rescue and maintenance of the corpus luteum of pregnancy for continuous progesterone secretion and support of gestation prior to placental take over.
• HCG levels peak at 6-12 days after fertilization, averaging at 9 days.
• HCG levels increase during the 6th week of pregnancy and decrease during the 2nd and 3rd trimester.
• HCG is used in the determination of pregnancy, diagnosis of incomplete abortion, and diagnosis of ectopic pregnancy.
• HCG is used in the diagnosis of non-trophoblastic tumors, such as sacrococcygeal teratoma, and gestational trophoblastic disease, including molar pregnancy.
• HCG is used in screening for Trisomy 21, where continuously increased levels indicate Down Syndrome, Choriocarcinoma, and Molar pregnancy.
• A good pregnancy test should be fast, accurate and specific, reacting specifically with the B- subunits because LH, FSH and TSH share alpha subunits with HCG but lack B- subunit.
• A good pregnancy test should be reproducible and sensitive, being precise and sensitive to decrease amounts.
• Bioassays for pregnancy testing were introduced in 1928 by Ascheim-Zondek, Friedman-Hoffman, Frank-Baerman, Kupperman, Hogben, and Galli-Mainini.
• Immunoassays for pregnancy testing employ an Ag-Ab reaction.
• False positives may also appear on test kits used past their expiration date.
• In Hemagglutination Inhibition, anti-HCG antiserum is neutralized in the presence of HCG, preventing agglutination.
• High titers of pituitary hormones (LH, FSH, and TSH) can cause false positives in pregnancy tests.
• In Latex Agglutination Inhibition, the addition of HCG coated cells/latex no longer binds with Anti-HCG antiserum since all HCG has neutralized Anti-HCG antiserum, resulting in no agglutination.
• Most kits can detect hCG levels as low as 25.
• Mole, teratomas and other forms of malignancies can cause false positives in pregnancy tests.
• Agglutination is the (+) result.
• DAP test, Natatel, Planosec, Prepuerin are examples of pregnancy tests that use Latex Agglutination.
• Evaporation lines may appear on many home pregnancy tests if read after the suggested 3-5 minute window or reaction time.
• Low sensitivity of lab animals due to seasonal variations or depression of toxic urine can cause false negatives in pregnancy tests.
• Presence of hCG in the urine specimen of a pregnant woman will bind with the antibodies in the test kit, resulting in a (+) result.
• Seasonal variation of experimental animals can cause false positives in pregnancy tests.
• Ectopic pregnancy and incomplete abortion can cause false positives in pregnancy tests.
• Less sensitive urine tests and qualitative blood tests may not detect early pregnancy.
• Quantitative blood tests are the most sensitive urine tests that usually detect HCG shortly after implantation (5 to 7 days after conception).
• Hemagglutination Inhibition (HAI) and Latex Agglutination Inhibition (LAI) employ the same principle but use different markers, with HAI marker being Sheep RBC and LAI marker being latex particle.
• Testing is done too early in the course of pregnancy can cause false negatives in pregnancy tests.
• Latex Agglutination or Hemagglutination involves coating a latex/RBC particle with anti-HCG antiserum, which will agglutinate in the presence of HCG.
• Variety of drugs like chlorpromazine derivatives, phenothiazine, and aspirin can cause false positives in pregnancy tests.
• Immunochromatography, used in the pregnancy test kits available in the market, involves the presence of highly specific antibodies against the β-sub unit of the hCG.