Serostatus is a term used to refer to the presence or absence of specific substances in the blood serum. Most commonly, this medical test is looking for specific antibodies in an effort to diagnose a particular disease.
A person's test results can be seropositive or seronegative or indeterminate. Seronegative refers to the absence of the specific antibodies (or other substance) that were being tested for. Seropositive refers to the presence of the specific antibodies that were being tested for.
These tests are most commonly used to identify HIV infection and to find rheumatoid factor, although it is possible to apply this concept to hundreds of other diseases and medical conditions. To understand the result, it is necessary to know what antibodies the test was looking for, because a person who is seropositive for any one condition is not any more likely to be seropositive for another, unrelated condition.