Pregnancy Testing – Types of hCG Tests

What is a Pregnancy Test?

A pregnancy test is used to confirm pregnancy and uses the urine or blood to detect the presence and levels of certain hormones which would be indicative of the pregnant state. There are a number of hormones, including progesterone and early pregnancy factor, which can be used to confirm pregnancy but the hormone that is most commonly evaluated is human chorionic gonadotropin (hCG).

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Tests to Diagnose Pregnancy

Human Chorionic Gonadotropin Test

HCG is usually detectable in the blood or urine of a pregnant woman within 10 days of fertilization (after implantation of the fertilized ovum in the uterus) and it gradually increases in the first trimester (first 12 weeks) of pregnancy and then falls as pregnancy progresses. Blood samples usually give more accurate results in early pregnancy than urine samples. Accuracy with urine samples increases when the test is done 2 weeks after a missed period.

There are four main types of hCG assays are used :

  • Radioimmunoassay
    • Sensitivity – 5 mIU/mL.
    • It takes 4 hours to complete the test.
    • First positive at 10 – 18 days after conception or 3 – 4 weeks of pregnancy.
  • Immunoradiometric assay (more sensitive)
    • Sensitivity – 150 mIU/mL.
    • It takes 30 minutes to complete the test.
    • First positive at 18 – 22 days following conception or 4 weeks of pregnancy.
  • Immunoradiometric assay (less sensitive)
    • Sensitivity – 1500 mIU/mL.
    • It takes only 2 minutes to complete the test.
    • First positive at 25 – 28 days after conception or 5 weeks of pregnancy.
  • Enzyme-linked immunosorbent assay – ELISA (more sensitive)
    • Sensitivity – 25 mIU/mL.
    • It takes 80 minutes to complete the test.
    • First positive at 14 – 17 days after conception or 3.5 weeks of pregnancy.
  • Enzyme-linked immunosorbent assay – ELISA (less sensitive)
    • Sensitivity – less than 50 mIU/mL.
    • It only takes 5 – 15 minutes to complete the test.
    • First positive at 18 – 22 days following conception or 4 weeks of pregnancy.
  • Fluoroimmunoassay
    • Sensitivity – 1 mIU/mL.
    • It takes 2 – 3 hours to complete the test.
    • First positive at 14 – 17 days after conception or 3.5 weeks of pregnancy.

The sensitivity of the assay will determine how early a pregnancy can be detected. The most common pregnancy tests currently used are sensitive to 25 mIU/mL. Pregnancy tests can be broadly divided into those that are conducted at home (usually a urine test) and tests conducted in a laboratory by using blood specimens.

Related Articles

  1. Qualitative and Quantitative Blood Tests and Levels
  2. Home Pregnancy Tests – FAQ, Information, Use and Results
  3. Pregnancy Test Results – Causes of False-Positive and False-Negative Readings
  4. No Period

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