Pregnancy Test (Blood)

Diagnostic Use

This test is suitable for diagnosing and monitoring pregnancy, ectopic pregnancy, and threatened abortion, and as a tumour marker for trophoblastic disease (hydatidiform mole or choriocarcinoma) or other tumours.

PREGNANCY

hCG level doubles every 2 days in early pregnancy.
hCG values > 200,000 are unusual in singleton pregnancies. Values higher than this occur in twin pregnancies, molar pregnancies, and trophoblastic tumours.
Ectopic pregnancies often have a lower than average hCG for dates and slower rate of increase.
The half life of hCG is 12 to 48 hours. Following birth or termination of pregnancy, serum hCG returns to undetectable values within a month, in most patients, although some take longer. Persistence of hCG should raise suspicion of retained products of conception.
TUMOUR MARKER

The hCG assay used at Middlemore Laboratory (Roche HCG Plus Beta) is able to measure all the variant forms of hCG found in association with tumours. When monitoring patients, the hCG test must always be performed by the same laboratory (different methods may give significantly different results).
The recommended monitoring protocol is as follows: weekly monitoring until 2 consecutive specimens show non-detectable levels, then monthly monitoring for up to 12 months. The monitoring interval may then be increased to 3 to 6 months over the next year.
POSTMENOPAUSAL hCG

The normal pituitary secretes a low level of hCG, which increases after menopause in women. hCG levels up to 28 IU/L have been seen in postmenopausal women in the absence of neoplastic disease (ref 3). Pituitary hCG can be distinguished from neoplastic production by giving subjects a high-estrogen oral contraceptive pill for 3 weeks, which will suppress pituitary hCG.

END-STAGE RENAL DISEASE

hCG may be elevated in end-stage renal disease (ref. 4). The level should remain fairly constant if the patient is not pregnant. A serum progesterone level may be helpful in ruling out pregnancy.