[Value of derivative spectrophotometry for the determination of plasma and urinary hemoglobin. Comparison with the method using Allen's correction].

We are proposing a technique enabling the dosage of hemoglobin in plasma or urine using spectrophotometry in derivative double dash. Around 420 nm hemoglobin has an elevated molecular extinction factor but the absorption of natural pigments creates a non-negligible interference in the classic spectrophotometric methods. On the contrary, the use of the derivative double dash enables to practically eliminate the background noise and to obtain a specific signal for hemoglobin while keeping an excellent sensitivity. In the plasma, where hemoglobin is entirely linked to haptoglobin, the dosage is done by direct reading (while in the urine the presence of several pigment forms requires the use of Drabkin's reagent. The method is simple, quick, precise and enables to titrate 1 mg.l (or 0.015 mumole.l-1) of hemoglobin. The influence of bilirubin is negligible. The comparison with a method using Allen's correction shows the superiority of the former as far as precision and accuracy are concerned, by avoiding the danger of a non-negligible systematic error.