Increases of creatine kinase MB and cardiac troponin T in serum of a patient with uterine leiomyosarcoma.

concentrations were significantly different between HbSS and HbSC patients (P 5 0.016), and between HbSS patients and HbAA controls (P ,0.0001), as determined by the Student t-test. Our observation is consistent with the establishment of RBC folate concentrations during hemopoiesis and a subsequent decrease during circulation, causing higher RBC folate concentrations in young circulating RBCs (2, 3 ). At steady state, subjects with HbSS, HbSC, and HbAA have apparent RBC half-lives of 5–10, 12–25, and 25–40 days, respectively (4 ). The association with RBC turnover became apparent by an inverse relationship between steady-state RBC folate and Hb (Fig. 1, top) and a positive relationship between steady-state RBC folate and the sum of the RBC polyamines spermidine and spermine (Fig. 1, bottom). The latter is a sensitive marker of mean RBC age, with young RBCs having the highest concentrations (4 ). One may argue that the use of special cutoff values, e.g., those derived from HbSS and HbSC patients with optimal folate status, can circumvent the confounding dependence of RBC folate on RBC age. Special cutoff values may, however, cause low sensitivity because of the heterogeneity of RBC turnover in patients classified according to Hb types and the occasional occurrence of hemolytic and vaso-occlusive crises in SCD. For example, patients with concomitant hereditary persistent HbF will have lower RBC turnover. In addition, the frequently occurring concomitant a-thalassemia also modifies disease activity. It might, therefore, be better to use serum folate and preferably homocysteine for the establishment of folate status, although the latter also depends on vitamins B12 and B6, and other factors. Our proposal is in accordance with a previous recommendation to use fructosamine and not glycohemoglobin or HbX1c in SCD patients because, in contrast to HbX1c and glycohemoglobin, fructosamine is not confounded by dependence on RBC turnover rate (4 ). References 1. Van der Djis FPL, Schnog J-JB, Brouwer DAJ, Velvis HJR, Van den Berg GA, Bakker AJ, et al. Elevated homocysteine levels indicate suboptimal folate status in pediatric sickle cell patients. Am J Hematol 1998;59:192–8. 2. Zettner A, Boss GR, Seegmiller JE. A long-term study of the absorption of large oral doses of folic acid. Ann Clin Lab Sci 1981;11:516–24. 3. Heseker H, Schmitt G. Effect of long-term supplementation of folate on folate status in plasma and erythrocytes. J Nutr Sci Vitaminol 1987;33: 163–8. 4. Martina WW, Martijn EG, Van der Molen M, Schermer JG, Muskiet FAJ. b-N Terminal glycohemoglobins in subjects with common hemoglobinopathies: relation with fructosamine and mean erythrocyte age. Clin Chem 1993;93: 2259–65.