Human albumin production in the serum of rats receiving hMSCs, CD34⁺ cells, or non-hMSCs/CD34^- cell transplantation as evidenced by ELISA. Three elevated doses of purified human albumin (included in the kit) were mixed to the normal rat serum to test the sensitivity of detecting human albumin in rat serum. Rat plasma was collected and human serum albumin was assayed with ELISA at days 14, 28, and 56. Two rats were used in each group for CD34⁺ cells and non-hMSC/CD34^- cell transplantation, respectively. Four rats were used in each group for hMSCs. We included in the ELISA 5 different concentrations of human albumin to create a standard curve from which to extrapolate the absorbance reading for each test sample. A triplicate sample of diluent alone was used to set the zero point for the ELISA. The final absorbance obtained in our test samples was calculated after subtracting the zero point absorbance. Error bars indicate standard deviations (SDs). N.D. indicates not determined.