Present day practice Erroneously high results in

As manual methods for estimating the concentration of iron in serum are replaced by automated methods it is not always appreciated that the results may not be identical. Babson and Kleinman (1967), in their expei iments with 'serum protein solutions', found that the AutoAnalyzer procedure of Young and Hicks (1965) gave iron results which did not agree with a manual method (Peters, Giovanniello, Apt, and Ross, 1956) and were erroneously high. They showed that the discrepancy was due to a Donnan equilibrium effect on the dialysis rate of the ferrous iron, an essential step in the AutoAnalyzer procedure. Because of this effect, the protein present in the test 'serum solutions' led to a greater dialysis rate than in the standard iron solutions. After the addition of 5% NaCl to the diluent reagent (1 % ascorbic acid in 0 1 M HCI), they found that the automated procedure gave iron assays which agreed with the manual method and gave good recovery of iron added to 'serum protein solutions'. This modification of the automated procedure is now used routinely by most laboratories. However, when patients' sera are analysed, although the