During the first half of the 20th century, the complete blood count (CBC), one of the most commonly ordered laboratory tests, was performed using exclusively manual techniques:
●Blood cell counts (red cells, white cells, platelets) were performed using appropriately diluted blood samples and a ruled counting chamber (hemocytometer).
●Hemoglobin concentration was analyzed colorimetrically by the cyanomethemoglobin method.
●The hematocrit (Hct), also called packed cell volume, was measured by high speed centrifugation of a column of blood, either in a specially designed tube (the Wintrobe tube) (picture 1), or in sealed microcapillary tubes (ie, the "spun" hematocrit, often obtained by fingerstick blood collection) (picture 2).
●The white blood cell differential was obtained by examining and enumerating by class (eg, granulocytes, lymphocytes, monocytes) 100 to 200 individual white blood cells on a suitably stained blood smear.