A positive blood or urine pregnancy test without an intrauterine or an ectopic pregnancy is also known as a 'false positive' pregnancy test. A 'phantom hCG test' is a false positive blood (not urine) pregnancy test (usually up to about 700 mIU/cc hCG) without a pregnancy being present. A phantom blood positive pregnancy test is usually due to an error in the laboratory test. In many cases of phantom hCG the urine pregnancy test will be negative.
Conditions usually present with a phantom hCG test:
- The urine pregnancy test is negative, and
- The blood hCG test is positive but usually does not rise (or drop) according to expectation and remains often below 700 mIU/mL.
There are several possibilities which may produce a phantom hCG:
False laboratory test
The phantom hCG test can be positive because the laboratory assay falsely identifies other chemicals as hCG. That is because certain chemicals (antibodies) generated in the body against other human antibodies (IgG against IgG) may bind both human and animal antibodies (heterophilic antibodies) and they may interfere with commercial hCG tests, making it falsely positive.
The paraneoplastic symptom is a condition where other parts of the body such as tumors of different body parts produce hCG, the pregnancy hormone. This could include the ovaries, uterus, or even the lung.
If you have a positive blood hCG which is not rising, the first thought is usually a miscarriage. But with the phantom hCG no pregnancy is present, and a confirmatory urine test will be negative. When a urine pregnancy test is not done in addition to a questionable quantitative blood hCG test, a patient may receive unnecessary surgery, tests, and treatments.