17-AAG 40 mg/m(2) (median dose, 70 mg) was well tolerated when given daily for 5 days every 3 weeks.

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The utilization of folic acid during erythropoiesis is widely known and accepted in medical literature and deficiency is known to cause a characteristic megaloblastic anemia resulting from the inhibition or ineffective synthesis of DNA. Although the resultant megaloblastic anemia may take considerable time before evidence or symptoms present, there are more acute changes visualized on peripheral smear that are representative of a functional folate deficiency. In addition to erythrocyte macrocytosis, hypersegmentation of neutrophils can also be seen. Often times, despite these visualized changes measurement of serum folate and/or total red cell folate yields a result within the accepted “normal” range of the assay. It has been demonstrated that these visualized characteristics represent a functional folate deficiency and can be overcome with folic acid supplementation regardless of the measured folic acid levels indicating a yet to be understood mechanism of folate utilization. Here, we sought to measure the folic acid levels in the earliest erythrocyte progenitors in peripheral circulation, the reticulocytes. Methods Reticulocytes were isolated using anti-CD71 (the transferrin receptor) coated magnetic beads. After separation, a sample slide was made utilizing methylene blue for visual confirmation of reticulocyte isolation. The reticulocytes were then lysed with citric acid and a Nanodrop-1000 spectrophotometer was used to determine absorbance at 413 nanometers. This absorbance was used to determine the sample hemoglobin concentration from a simple calibration curve. The sample folic acid level was then determined using the lysing method utilizing mouse monoclonal anti-folate binding protein, paramagnetic particles coated in anti-mouse IgG, human serum albumin and milk folate binding protein. Results were calculated as nanogram of folate per gram of hemoglobin. Results Twenty-five samples from normal individuals, not taking folate supplements, were analyzed. The range of results was 2.51 to 17.38 with a mean level of 9.61. Conclusion This protocol effectively and efficiently allows for isolation of reticulocytes in numbers high enough for measurement of folate in nanogram per gram of hemoglobin. By this method we show the normal reticulocyte folate level to be approximately 3-15 ng/g of Hgb. This figure is consistent with the normal red cell folate concentration. Further analysis is planned for comparing these results in patients with a suspected functional folate deficiency but “normal” red cell folate levels. Efficient isolation of reticulocytes and measurement of folate levels will allow us to probe the underlying cause of acute folate deficiency seen in very sick patients. Disclosures: No relevant conflicts of interest to declare.

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