Suitability of plastic collection tubes for cyclosporine measurements.

together with the results of the low ferritin patients of the previously mentioned anemic cohort (five men and eight women). In the group with ferritin values below the reference interval (,25 mg/L), 5 out of 11 men had CDTect values $20 units/L and 8 out of 18 women had CDTect values $26 units/L. Therefore, a disproportionate number of high CDTect values were observed in anemic and nonanemic patients with low ferritin values. Retrospectively, these patients showed no indications for alcohol abuse. In the literature, the specificity of CDT for nondrinking men and women is at least 90% and has been reported as high as 100% (1, 2). From these results it can be concluded that higher transferrin production (to cope with higher iron demand, for example) involves higher CDT concentrations, which frequently exceed the cutoff values. It can be expected that other conditions with low iron stores also show an increased percentage of false-positive CDT values. This was actually shown in hereditary hemochromatosis, where iron depletion with phlebotomy caused an increase in serum CDT, also above the reference interval (3). Finally, we recently found that reference values of CDTect in nondrinking perimenopausal women were dependent on the frequency of menstruation in the past year. The upper limit of the reference values was 26 units/L for preand perimenopausal women (in accordance to the manufacturer) but was significantly lower for postmenopausal women (22 units/L, P ,0.0001) (4). In conclusion, low iron status or high iron demand involves higher transferrin synthesis, probably with a proportional increase of CDT isoforms. Therefore, low ferritin status should be taken into account as a cause for unexplained high CDT results. The use of the ratio CDT/ transferrin seems to have an advantage in this situation; however, it can induce false-positive outcomes if transferrin concentrations are low (5). References 1. Stibler H. Carbohydrate deficient transferrin in serum: a new marker of potentially harmful alcohol consumption reviewed. Clin Chem 1991;37:2029–37. 2. Conigrave KM, Saunders JB, Whitfield JB. Diagnostic tests for alcohol consumption. Alcohol Alcohol 1995;30:13–26. 3. Jensen PD, Peterslund NA, Hjelm Poulson J, Jensen FT, Christensen T, Ellengaard J. The effect of iron overload and iron reductive treatment on the serum concentration of carbohydrate-deficient transferrin. Br J Hemat 1994; 88:56–63. 4. van Pelt J, Keijzer JJ, Goevaers CGC, Leusinh CL. Reference values, sensitivity and specificity of CDTect in perimenopausal women. Alcohol Clin Exp Res 1998;22:180A. 5. Stowell CI, Fawcett JP, Brooke M, Robinson GM, Stanton WR. Comparison of two commercial test kits for quantification of serum carbohydrate deficient transferrin. Alcohol Alcohol 1997;32:507–16.