The micro estimation of serum iron and iron-binding capacity in normals and in disease.

It is now well established that the transport of iron in plasma is by a specific iron-binding P. globulin component of the plasma protein which has been isolated (Schade and Caroline, 1946). Holmberg and Laurell (1945) concluded that the amount of iron in normal plasma by no means attains the limit of saturation of the specific ironbinding protein. This saturation limit has been termed by Laurell (1947) the iron-binding capacity of plasma, and he, as well as Rath and Finch (1949) and Cartwright and Wintrobe (1949), has shown that the simultaneous estimation of serum iron and iron-binding capacity, giving the percentage saturation, may be more informative than the simple determination of serum iron. Apart from the thiocyanate method of Burch, Lowry, Bessey, and Berson (1948), which requires only 20 c.mm. of serum, most methods for the estimation of serum iron require at least 1 ml. of serum. However, since this investigation was begun a method using a new colorimetric reagent for iron, o-tolidine, has been described (BudtzOlsen, 1951) requiring only 0.75 ml. serum for duplicate determinations. For the iron-binding capacity, only two methods have been described (Laurell, 1947; Cartwright and Wintrobe, 1949; Rath and Finch, 1949) and both require at least 2 ml. serum. In an investigation of serum iron and iron-binding capacity in infants and the newborn it was felt essential to devise a method suitable for the small amounts of blood which could be obtained by heel or finger prick rather than to limit the scope to those instances where adequate amounts could be obtained by venipuncture. From a review of the literature it appeared that the o-phenanthroline method of Heilmeyer and Plotner (1937), as modified by Laurell (1947), for both serum iron and ironbinding capacity could be most readily adapted as a micro-method. It possessed the advantage that fundamentally the same procedure was used for the two estimations, and that the presence of small amounts of haemoglobin did not introduce any appreciable error.