Methemoglobinemia and severe self-limiting hemolytic anemia due to glucose-6-phosphate dehydrogenase (G-6-PD) deficiency appeared after intravenous use of toluidine blue to visualize parathyroid tissue during subtotal thyroidectomy. Determination of G-6-PD should be a part of the patient's preoperative baseline laboratory study when the use of toluidine blue is contemplated. If deficiency is documented, the drug should be administered only in an extraordinary circumstance and after adequate preparation to project the susceptible patient.
Teunis BS, Leftwich EI, Pierce LE. Acute Methemoglobinemia and Hemolytic Anemia Due to Toluidine Blue. Arch Surg. 1970;101(4):527-531. doi:10.1001/archsurg.1970.01340280079021