Urine pregnancy testing is a screening tool and should only be used for the qualitative detection of HCG for early determination of pregnancy.
In urine, intact and fragmented HCG molecules are present. Fragmented HCG molecules are elevated in mid pregnancy and in certain malignancies. Urine pregnancy test kits may pick up a fragmented HCG molecule, causing a false negative urine pregnancy result even though a patient is pregnant.
Results should be used in the context of the patient clinical information (medical history, symptoms, results of other tests, clinical impression) and/or confirmed using a serum quantitative hCG assay prior to performance of any critical medical procedure.