Diagnostic Use
A preliminary test to screen pregnancy by detecting hCG in urine. In general, hCG can be detected in urine (and serum) after 7 – 10 days post conception. Any positive result should be confirmed by a blood pregnancy test.
Interpretation
See the limitations and interference section below for information of causes of false positive or false negative results. In general, if pregnancy is expected OR if the result does not match the clinical history, confirmation by serum hCG is recommended.
Note: Heterophile antibody will not cause a false elevation in urine but can in serum.
Test Method
Test performed by: LabPLUS Automation
INNOVACON 1 STEP HCG (Poly & monoclonal antibodies)
Limitations / Interference
While the test generally performs well, there are some instances in which a false negative or false positive result can occur, including:
1. Very borderline results may be subject to false positive or negative observer bias as the test strips are read by a human.
2. Very dilute urine (e.g. early in pregnancy and or patient on an IV drip with rapid urine formation) can cause a false negative.
3. Very early pregnancy, i.e. shortly after implantation may cause a false negative (manufacturer claims that the test detects the presence of HCG at the sensitivity of 25 IU/L).
4, Testing in late first or second trimester may cause a false negative. Beta core fragment of hCG (bcf-hCG) is a degradation product of intact hCG and is the main form of hCG during the late first and entire second trimester. Urine pregnancy test cannot detect this form and when urine contains predominantly bcf-hCG, it can give a false negative result (variant hook effect). If the patient has missed 2 or more menstrual cycles, then serum pregnancy test (serum hCG) should be performed. Bcf-hCG is not present at significant concentrations in serum and will not interfere.
5. Non-pregnancy causes of genuinely raised urine hCG include trophoblastic disease, testicular tumour, lung cancer, breast cancer (if hCG secreting), pituitary hCG (can be seen in peri/post-menopausal women, premature ovarian failure or benign familial syndromes).