Limitations

As with any immunochemical reaction, unknown interferences from medications or endogenous substances may affect results.

Interfering substances (such as heterophile antibodies, non-specific proteins, or hCG-like substances) may falsely depress or falsely elevate results.  These interfering substances may cause false results over the entire range of the assay, not just at low levels, and may indicate the presence of hCG when there is none.

If the hCG level is inconsistent with, or unsupported by, clinical evidence, results should be confirmed by an alternate hCG method.  This may include the qualitative testing of urine.  The absence of urinary hCG may suggest a falsely elevated serum result.  Results may also be confirmed by performing serial dilutions of the sample.  Usually, but not always, samples that contain interfering substances exhibit nonlinear results when diluted.

Detection of very low levels of hCG does not rule out pregnancy.  Low levels of hCG can occur in apparently healthy, non-pregnant subjects.  Because hCG values double approximately every 48 hours in a normal pregnancy, patients with very low levels of hCG should be re-sampled and retested after 48 hours.

Post-menopausal specimens may elicit weak positive results due to low hCG levels unrelated to pregnancy.  With a weak positive result, it is good laboratory practice to resample and retest after 48 hours, or to test with an alternate hCG method.

Elevated hCG levels have been associated with some abnormal physiological states (e.g., trophoblastic and non-trophoblastic neoplasms) and the results of this test should not be used in the diagnosis of these abnormal states.  There have been reports of people receiving unnecessary medical treatment and surgery, including chemotherapy and hysterectomy, when hCG results were used in the diagnosis of abnormal states.

Because of the high degree of sensitivity of the assay, specimens tested as positive during initial days after conception may later be negative due to natural termination of the pregnancy.  Natural termination occurs in 22% of clinically unrecognized pregnancies and 31% of pregnancies overall.  It is good laboratory practice to re-sample and retest weak positive results after an additional 48 hours.

Do not use this assay for TUMOR DETECTION.

** If the specimen is centrifuged BEFORE a complete clot forms, the presence of fibrin may cause erroneous results.  **