To the Editor.—Cooper et al1 in this Journal reported a new semiquantitative method for iron determination. However, they added iron to their samples of blood vitro. We used their method to estimate iron present in the blood of patients (ie, iron present in vivo) and would like to record that their method seems useful.
We reported2 studies of a sample of 100 patients requiring serum iron determination for numerous reasons. Iron concentration was determined by the routine spectrophotometric method used in our laboratory and by the semiquantitative method under study in all cases. Both methods were performed by different technicians blindly, ie, they were unaware of each other's results.
The screening semiquantitative method was performed as described by Cooper et al1 except that serum rather than plasma was used. To 1 ml of serum one drop of thioglycolic acid was added, followed by one drop of