Objective      To investigate the effect of albumin-bound indoxyl sulfate on erythrocytes and related mechanism.       Methods      Different concentrations of indoxyl sulfate were bound to 4% albumin. Erythrocytes with 0.4% hematocrit were prepared from normal adults. Forward scatter was used to estimate erythrocyte volume. Phosphatidylserine-exposure from annexin V binding was used to check eryptosis. Erythrocyte intracellular free calcium concentration ([Ca

2+

]

i

) was detected by Fluo3-fluorescence and assayed by flow cytometry. Hemolysis from hemoglobin release was

estimated with an enzyme-mark analyzer. Statistical analysis was made with SPSS18.0 software.       Results      Exposure to albumin-bound indoxyl sulfate for 48 hours significantly decreased erythrocyte volume (1603.33±8.50 vs 742.67±14.04

P0.05)

and increased eryptosis (0.26±0.06 vs 10.32±1.64

P0.05)

[Ca

2+

]

i

and hemolysis ratio in a dose-dependent manner (P0.05). The damage effect of albumin-bound indoxyl sulfate on erythrocytes was weakened in the absence of Ca

2+

in the supernatant.       Conclusion      Albumin-bound indoxyl sulfate induces eryptosis through calcium influx

which is an important mechanism of anemia in uremic patients. Eliminating albumin-bound indoxyl sulfate might alleviate renal anemia.