Interference of methylene blue with CO-Oximetry of hemoglobin derivatives.

Methylene blue (MB) is frequently used as an antidote in treating methemoglobinemia (1) because it facilitates the reducing activity of the NADPH-dependent methemoglobin reductase system in erythrocytes (2). However, MB absorbs strongly between 550 and 700 nm (Fig. 1 ), the same spectrophotometric region as that of the various hemoglobin derivatives: oxyhemoglobin (O2Hb), deoxyhemoglobin (HHb), methemoglobin (MetHb), and carboxyhemoglobin (COHb). To evaluate the potential magnitude and direction of errors linked to the presence of MB for the results for total hemoglobin (tHb) and its derivatives, we evaluated six CO-Oximeters. The wavelengths used by each instrument for these determinations are as follows: IL 482 (Instrumentation Laboratory, Lexington, MA), 535, 585.2, 594.5, and 626.6 nm; CCD 270 (Chiron Diagnostics, Medfield, MA), 557, 577, 597, 605, 624, 635, and 650 nm; CCD 835 (Chiron; wavelengths not communicated); OSM3 (Radiometer, Copenhagen, Denmark), 535, 560, 577, 622, 636, and 670 nm; ABL 520 (Radiometer; same wavelengths as OSM3); AVL 912 (AVL Scientific Corp., Roswell, GA), 530, 536, 542, 548, 554, 560, 566, 572, 578, 584, 590, 604, 612, 622, 630, 640, and 648 nm.