Hi, and thanks for your medical question on eHealth's Ask a Doctor forum.

Well, the home pregnancy tests can come back false positive. False positive is seen due to a faint evaporation line as the urine crosses the test, early reaction time or seeing the result early, or delayed time when results are seen late, or due to miscarriage.

Repeat the ELISA test for pregnancy in a lab or at a doctor’s, or consult a gynecologist for a trans- vaginal ultrasound for confirmation. The ultrasound is most confirmatory.
It is difficult to comment beyond this on net. Hope this helps. Take care!