Interference by o-phenanthroline in the radioimmunoassay of angiotensin II in small volume blood samples.

OBJECTIVES: To investigate the ratio of enzyme inhibitor volume to blood volume in angiotensin II (Ang II) blood collection tubes. DESIGN AND METHODS: Whole blood was mixed with known volumes of inhibitor prior to angiotensin II analysis. RESULTS: Imunoreactive Ang II levels increased at low blood volume to high inhibitor volume ratios, due to interference by o-phenanthroline. CONCLUSION: To prevent falsely elevated Ang II levels in low volume blood samples an appropriate volume of inhibitor solution must be used.