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LIMITATIONS IN HCG TESTING
• This assay is capable of detecting only whole molecule (intact) hCG, which is the predominant form of
hCG in early pregnancy. It cannot detect the presence of hCG fragments or free subunits.
• In later term pregnancies (generally beyond the first trimester), occasional urine samples can contain
very high levels of hCG fragments. Therefore, for urine testing, the OSOM hCG Combo Test is most
effective when used for the detection of pregnancy in its earlier stages.
• For diagnostic purposes, hCG test results should always be used in conjunction with other methods
and in the context of the patient’s clinical information (e.g., medical history, symptoms, results of
other tests, clinical impression, etc.). Ectopic pregnancy cannot be distinguished from normal
pregnancy by hCG measurements alone.
(2,3)
• If the hCG level is inconsistent with, or unsupported by, clinical evidence, results should also be
confirmed by an alternative hCG method. If a serum specimen is initially tested qualitatively,
alternative methods may include the quantitative testing of serum or the qualitative testing of
urine.
(4)
The absence of urinary hCG may suggest a falsely elevated serum result. Additionally,
results may be confirmed by performing serial dilutions of the sample as usually, but not always,
samples that contain interfering substances exhibit nonlinear results when diluted. Test results
should be confirmed using a quantitative hCG assay prior to the performance of any critical
medical procedure.
• Interfering 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. As with any immunochemical reaction, unknown
interferences from medications or endogenous substances may affect results.
• Infrequently, hCG levels may appear consistently elevated and could be due to, but not limited to,
the presence of the following:
(5-8)
Heterophilic antibodies: Patients routinely exposed to animals or to animal serum products,
can be prone to this interference and anomalous values may be observed
Trophoblastic or nontrophoblastic neoplasms: abnormal physiological states that may falsely
elevate hCG levels.
(9,10)
This test should not be used in the diagnosis of these conditions.
Nonspecific protein binding
hCG like substances
• Specimens from patients who have received preparations of Mouse Monoclonal Antibodies for
diagnosis or therapy may contain Human Anti-Mouse Antibodies (HAMA). Such specimens may
demonstrate either falsely elevated or falsely depressed results when tested with assay kits which
employ Mouse Monoclonal Antibodies.
(11,12)
• Because of the high degree of sensitivity of the assay, specimens tested as positive during the
initial days after conception may later be negative due to natural termination of the pregnancy.
Overall, natural termination occurs in 22% of clinically unrecognized pregnancies and 31% of other
pregnancies.
(13)
In the presence of weakly positive results, it is good laboratory practice to sample
and test again after 48 hours.
• If the test band appears very faint, it is recommended that a new sample be collected 48 hours
later and tested using another OSOM hCG Combo Test Device.
• Dilute urine specimens may not have representative levels of hCG.
INTERPRETATION OF TEST RESULTS
Positive
Two separate black or gray bands — one at “T: Test” and the other at “C: Control” — are visible in the
results window, indicating that the specimen contains detectable levels of hCG. While the intensity of
the test band may vary with different specimens, the appearance of 2 distinct bands should be
interpreted as a positive result.
Negative
If no band appears at “T” and a black or gray band is visible at the “C: Control” position the test can be
considered negative, indicating that a detectable level of hCG is not present.
Invalid
If no band appears at the “C: Control” position, the test is invalid. The test is also invalid if incomplete or
beaded bands appear at either the “T: Test” or “C: Control.” The test should be repeated using another
Test Device.
Note:
The test is valid if the control line appears by the stated read time regardless of whether the sample has
migrated all the way to the end of the sample window.