Note: the hCG assay in use at SydPath is being changed - August 2009

Assays: the assay is changing from the Siemens Advia Centaur to the Roche E170.

Reason: SydPath is upgrading the instruments used for routine hormone testing

Effects: the results are very similar up to 4000 U/L, about 10% lower up to 40,000 U/L and 20% lower at higehr concentrations

Reference Intervals: no change as a pregnancy test. The expectd values at various weeks of pregnancy have been updated.

Use in malignancy: patients being monitored with hCG as a tumour marker will have samples tested on both methods during a transition period.

General

Human Chorionic Gonadotrophin (hCG) is a hormone secreted from the placenta into the maternal circulation with a role in the maintenance of a viable pregnancy. The serum concentration of hCG is used for the detection and monitoring of pregnancy and some malignant conditions.

Normal Ranges in Non-pregnant people  

In normal women of child-bearing age the expected concentration of hCG in serum is less than 10 U/L, although usually it is less than 2 U/L. After menopause results up to 10 U/L are more common. hCG is less than 10 U/L in serum from males, and usually significantly lower. See table.

Diagnosis of Pregnancy  

Using routine laboratory methods hCG is first detectable in the circulation 1 - 2 weeks after conception. This is equivalent to the first week after implantation or about 3 - 4 weeks after the last normal menstrual period. When using hCG tests to exclude pregnancy, a negative serum test (<10 U/L) taken after the first missed period, or for less sensitive tests such as are commonly used for urine testing a negative result one week after the first missed period is recommended for certainty. To be confident that a pregnancy is present a serum hCG concentration greater than 25 U/L is desirable. If a concentration between 10 and 25 U/L is obtained on a pregnancy test, then a further sample in 1 - 2 days is suggested for confirmation. For women before the first missed period, a negative result does not exclude very early pregnancy and repeat testing may be needed to exclude pregnancy. See table.

hCG during pregnancy   

During the first weeks of pregnancy serum concentrations rise rapidly with a doubling time of about 2 days. This rate of rise slows and the peak hCG concentration is reached between 8 and 12 weeks gestation. The concentration then falls to a plateau which persists over the second and third trimesters. After delivery hCG falls with a half life of 1 - 2 days.

As can be seen from the table the expected values during pregnancy are very wide. This limits the use of hCG concentrations as a marker of the stage of pregnancy.

Abnormal hCG concentrations during pregnancy 

High levels may be found in patients with twin or multiple pregnancies or with gestational trophoblastic disease. Low levels may be a marker of non-viable pregnancy, eg ectopic pregnancy.

If the serum hCG concentrated takes more than 2 days to double in concentration during early pregancy, this should arouse suspicions of either a possible ectopic pregnancy or a non-viable intrauterine pregnancy. Gynaecological opinion should be sought in this instance. hCG is usually detectable in ectopic pregnancies but this is not a universal finding.

At hCG concentrations over 2500 U/L a normal intra-uterine pregnancy should be visible on trans-vaginal ultrasound. Note that hCG levels should never be used in isolation for diagnosis of any of the above conditions.

Causes of hCG elevation other than pregnancy    

Elevated concentrations of hCG are a common finding in the serum of patients with trophoblastic or other germ cell tumours and can be a valuable marker for monitoring these conditions. Other malignancies which may also be associated with increased hCG include lung, breast, gastrointestinal and ovarian cancers. Elevated serum hCG may also be found in some non-malignant disorders including inflammatory bowel disease, cirrhosis and duodenal ulcer. hCG has also been used as an anabolic agent in some sportspersons.