The Dengue IgG (ELISA) test is your definitive 'look-back' test. It is a high-precision blood test that detects the long-term 'memory' (IgG) antibodies your body produces after you have recovered from a Dengue infection. A positive result from this test confirms you have been exposed to the virus in the past. This is crucial for understanding your immune history. It is not the primary test for an active fever (that's IgM or NS1). However, it is a key tool in diagnosing a secondary infection, which is vital for your doctor to know. A simple blood draw provides this essential, historical data, giving your doctor a complete picture of your immune status.