Determination of nitrotyrosine concentrations in plasma samples of diabetes mellitus patients by four different immunoassays leads to contradictive results and disqualifies the majority of the tests.

All three ELISA methods were disqualified and conclusions previously derived from clinical experiments using these tests should be carefully reconsidered or reconfirmed. In the absence of a liquid tandem chromatography-mass spectrometry reference method, the luminescence test appears to be the method of choice for determination of nitrotyrosine in human plasma.