A positive ANA does not necessarily mean that you have Lupus. There are several other diseases that also have a positive ANA. However, most persons with active Lupus do have a positive ANA. There are 11 criteria used to determine if Lupus is present, a person must meet at least four (4) of those eleven criteria. The "Lupus Foundation" website has a new interactive link "Could I Have Lupus" which is really helpful to those who feel that their symptoms may be due to Lupus. It is informative and easy to understand.
With reference to your questions: "Does the high C3 negate the high level of DS DNA antibodies? & "do I have to have a low level of C3 in order to be diagnosed with lupus?"
First, let me give you a bit of explanation so that you'll understand the tests. The complement system is one of the natural defense mechanisms that protects our bodies from infections and perhaps tumors. Measurement of complement components aids in the diagnosis of immunologic disorders, especially those associated with deficiencies of complement components (such as multisystem rheumatic diseases, such as systemic lupus).
Decreased levels of C3 are associated with autoimmune disease, neonatal respiratory distress syndrome, bacteremia, tissue injury and chronic hepatitis. Decreased levels of C4 may indicate disseminated intravascular coagulation (DIC); acute glomerular nephritis, chronic hepatitis and SLE.
Increased levels of both C3 and C4, in addition to increased concentrations of C-Reactive Protein, are linked to acute inflammatory disease and tissue inflammation (As happens in Lupus).
So doctors are looking for indications of inflammation (increased C3 & C4) &/or indications of auto-immunity and/or kidney involvement (decreased C3 & C4).
If Lupus nephritis (kidney involvement) is indicated in the C3 & C4 compliments, the DS DNA test ( along with antinuclear antibodies and levels of Ig & IgM ratio) help to support the diagnosis of Lupus nephritis and helps to determine the extent of damage caused by the nephritis. The IgG/IgM ratio of anti-dsDNA antibodies represents a significant parameter used by doctors, to distinguish patients with lupus nephritis from those without renal involvement. So, one test does not negate the other. Evaluation of anti-dsDNAisotypes is simply a diagnostic tool to define subsets within Lupus (SLE) patients who have different clinical manifestations. In particular, the IgG/IgM ratio of anti-dsDNA antibodies are used as a diagnositc marker for lupus nephritis during the course of the disease.
All of the tests are used as aids in determining if a condition exists and the extent of that condition.
Also, please know that, for diagnosis, Anti-dsDNA antibodies are frequently detected in active SLE, but they are not specific for SLE as they are also present in up to 30% of other disease groups. Therefore, doctors will use the aggregate results of all tests, personal history, and presenting symptoms to make a diagnosis. All tests are merely parts of a combination of things used to make a determination.
I hope that this has been helpful to you. Please let me know if it confused you further and/or if you need further information!
Peace and Blessings