Sensitivity and specificity of transferrin saturation and serum ferritin as markers of iron status after intravenous iron dextran in hemodialysis patients

Abstract

This study was designed to investigate the effect of intravenous (i.v.) iron dextran (i.d.) on hematocrit (Hct), transferrin saturation (TS), and serum ferritin (SF) in hemodialysis patients treated with a constant dose of erythropoietin (EPO). The sensitivity, specificity, and predictive values of SF and TS for monitoring i.d. therapy were also assessed. All hemodialysis patients with baseline SF < 100 ng/mL or TS < 20%, with EPO dose unchanged 6 weeks before and 4 weeks after dosing with i.d. were included. I.d. (500 mg-1 g) was given as an infusion over 1 h. Patients receiving packed RBC or with active bleeding were excluded. Hct, TS, and SF were measured 2 weeks before and 4 weeks after i.d. Linear correlation coefficients between dose of i.d., changes in Hct, TS, and SF were calculated. The sensitivity, specificity, and predictive values of TS and SF were compared. A positive Hct response was defined as a > 5% increase from baseline 4 weeks after administration of i.d. Thirty-three patients (17 females) received a total of 51 doses of i.d. Mean +/- SD i.d. dose was 770 +/- 278 mg. Hct increased by a mean +/- SD of 4.8% +/- 9.9% (33.4% +/- 3.0% to 34.9% +/- 4.1% [p = 0.028]); SF rose by a median of 208.65% (mean +/- SD of 126.8 +/- 132.1 ng/mL to 325.3 +/- 222.0 ng/mL [p < 0.0001]; TS increased by a median of 53.8% (19.4% +/- 9.4% to 29.3% +/- 11.3% [p < 0.0001]) from baseline values. The correlations between dose of ID and percent changes in SF, TS, and Hct were poor (r2 < 0.02). The sensitivities and specificities were 74% and 36% (TS < 20% alone); 60% and 30% (SF < 100 ng/mL alone); and 33% and 67% (TS < 20% and SF < 100 ng/mL), respectively. The predictive values for positive responses were 48% for TS and 45% for SF when used alone, and 47% when both indices were used together. The predictive value increased to 65% when either SF < 100 ng/mL or TS < 20% were used. At a constant EPO dose, there was a statistically significant increase in Hct 4 weeks after i.d. administration in patients who were diagnosed with iron deficiency by using TS < 20% or SF < 100 ng/mL. The dose of i.d. administered was poorly correlated to changes in Hct, TS, and SF. Both TS and SF are non-specific and insensitive indicators for accurate diagnosis of iron deficiency in hemodialysis patients in EPO.