Which methodology is used for hemoglobin measurement with Drabkin's reagent?

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Hemoglobin is measured with Drabkin's reagent by converting all forms of Hb present in blood into a single, stable colored product, cyanmethemoglobin. When blood is lysed and mixed with Drabkin's reagent, potassium ferricyanide oxidizes the heme to methemoglobin, and cyanide binds to form cyanmethemoglobin. This colored compound absorbs light maximally at 540 nm, so a spectrophotometer can determine Hb concentration by comparing the sample’s absorbance to a calibration curve made with known cyanmethemoglobin standards. This cyanmethemoglobin method is favored for total hemoglobin because it yields a simple, linear, and stable signal compatible with automated analyzers. Other approaches listed—using HPLC for Hb typing, measuring directly without lysis, or using flow cytometry for Hb—do not provide the standard total Hb measurement via this reagent.