A urine pregnancy test may be falsely negative for a number of reasons. This may impact the fetus if the test was done prior to an imaging study or other exposure with teratogenic potential.
Possible explanations for a false negative urine pregnancy test:
(1) soon after fertilization with urine excretion of beta-HCG below the analytical level of detection
(2) early pregnancy and urine dilute
(3) specimen mixup
(4) reaction read too soon or too late
(5) use of a single monoclonal antibody that does not detect variant forms of HCG
(6) very high levels of free beta subunits causing a prozone-like or "hook" effect
(7) defective testing system
(8) technologist error
Problem
Solution
urine beta-HCG below the analytical level of detection
either test serum or repeat urine test in a few days
early pregnancy with dilute urine
measure specific gravity and urine creatinine to confirm dilute; perform serum test
specimen mixup
collect a new specimen and make sure that it is properly labeled
reaction read too soon or too late
repeat test reading result at the designated time
use of a single monoclonal antibody
test using a method utilizing a mixture of monoclonal antibodies
very high levels of core fragments
dilute the sample and repeat testing
defective test
repeat with new kit gives positive result
technologist error
provide corrective action
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