HCG blood test - quantitative

Definition

A quantitative human chorionic gonadotropin (HCG) test measures the specific level of HCG in the blood. HCG is a hormone produced during pregnancy.

See also:

• HCG urine test
• HCG blood test - qualitative

Alternative Names

Serial beta HCG; Repeat quantitative beta HCG; Human chorionic gonadotrophin blood test - quantitative; Beta-HCG blood test - quantitative; Pregnancy test - blood - quantitative

How the test is performed

Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The site is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.

Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm.

Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding.

In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.

How to prepare for the test

No special preparation is necessary.

How the test will feel

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

Why the test is performed

HCG appears in the blood and urine of pregnant women as early as 10 days after conception. Quantitative HCG measurements can help to diagnose abnormal preqnancies, such as ectopic pregnancies, molar pregnancies, and those that will miscarry. It is also used as part of a screening test for Down Syndrome.

This test is also done to diagnose abnormal conditions unrelated to pregnancy that can raise HCG levels.

Normal Values

HCG levels rise rapidly during the first trimester of pregnancy and then slightly decline.

What abnormal results mean

Higher-than-normal levels may indicate:

• Choriocarcinoma of the uterus
• Hydatidiform mole of the uterus
• Normal pregnancy
• More than one fetus -- for example, twins or triplets
• Ovarian cancer
• Testicular cancer (in men)

Lower-than-normal levels may indicate:

• Fetal death
• Incomplete miscarriage
• Threatened spontaneous abortion
• Ectopic pregnancy

What the risks are

There is very little risk involved with having your blood taken. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Taking blood from some people may be more difficult than from others.

Other risks associated with having blood drawn are slight but may include:

• Excessive bleeding
• Fainting or feeling light-headed
• Hematoma (blood accumulating under the skin)
• Infection (a slight risk any time the skin is broken)

Special considerations

Drugs that can decrease HCG measurements include diuretics and promethazine.

Drugs that can increase HCG measurements include anticonvulsants, anti-parkinsonian drugs, phenothiazine, and promethazine.

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References

Webster RA. Reproductive function and pregnancy. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 25.

Lee P, Pincus MR, McPherson RA. Diagnosis and management of cancer using serologic tumor markers. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa: Saunders Elsevier; 2006:chap 74.

Morrison LJ. General approach to the pregnancy patient. In: Marx J, ed. Rosen’s Emergency Medicine: Concepts and Clinical Practice. 6th ed. St Philadelphia, Pa: Mosby Elsevier; 2006:chap 176.