Why is serum heated at 56°C for 30 minutes before VDRL testing?

Heating serum at 56°C for 30 minutes before VDRL (Venereal Disease Research Laboratory) testing is primarily done to remove non-specific inhibitors. The presence of certain proteins and other components in serum can interfere with the detection of antibodies against the syphilis-causing organism, Treponema pallidum. Heating the serum denatures these proteins and thus helps eliminate potential non-specific reactions or false positives in the test results.

This step ensures that the test results are more reliable by reducing background noise that might obscure true antibody reactions. In essence, it enhances the specificity of the VDRL test, allowing for better detection of true positive reactions while minimizing the risks of contaminants that could adversely affect the outcome.