The ability to use indirect cyanmethemoglobin method using 20 µl of dried blood spots (DBSs) on filter paper for the analysis of haemoglobin (Hb) levels could be an important diagnostic tool for areas that have limited access to laboratory facilities. We assessed the validity of a method for Hb estimation in which a single drop of whole blood was directly taken on the filter paper. We collected 124 DBSs containing 20 µl of blood (filter paper A) and single drop of whole blood (filter paper B) from subjects living in Nainital, Uttrakhand. Estimation of Hb was done by indirect cyanmethemoglobin method in both the filter papers. A correction factor for predicting value of Hb from DBSs of single drop of whole blood was established. The Bland-Altman plot suggested that the difference in Hb values obtained by the single drop of blood and 20 µl of DBSs was within the 1.5 SD limits, suggesting high validity of the correction factor. The estimation of Hb using single drop of whole blood on filter paper after applying the correction factor provides results similar to indirect cyanmethemoglobin method using 20 µl of blood. Hence, single drop of whole blood on filter paper can be used as an alternate method for estimation of Hb in large scale community surveys.
Keywords: Dried blood spot method; Filter paper method; Hemoglobin estimation; Indirect cyanmethemoglobin method.