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Anemia and Iron Deficiencies among Long-Term Renal Transplant Recipients

Division of Nephrology and Dialysis, Department of Medicine III, University of Vienna, Vienna, Austria.

Correspondence to Dr. Matthias Lorenz, Division of Nephrology and Dialysis, Department of Medicine III, University of Vienna, Währinger Gürtel 18-20, A-1090 Wien, Austria. Phone: 43-1-40480-422; Fax: 43-1-40400-4392, E-mail: Matthias.Lorenz{at}nephro.imed3.akh-wien.ac.at

Abstract

ABSTRACT. Iron deficiency anemia after renal transplantation has not been systematically investigated. The prevalence of anemia and the indicators of iron deficiency among 438 renal transplant recipients were examined. Anemia was present in 39.7% of the patients. The prevalence of iron deficiencies, as indicated by a percentage of hypochromic red blood cells (HRBC) of 2.5%, was 20.1%. The majority of severely anemic patients exhibited HRBC values in the upper quartile. Positive associations of hemoglobin levels with creatinine clearance, serum transferrin levels, male gender, transferrin saturation (TSAT), polycystic kidney disease, and age were observed. Negative associations with erythropoietin therapy, use of azathioprine, serum ferritin levels, and body mass index were observed. The risk for anemia was closely related to the highest quartile of HRBC percentages (odds ratio, 2.35; 95% confidence interval, 1.48 to 3.75; P = 0.00029), whereas ferritin levels and TSAT conferred no risk for anemia. Therefore, assessment of the HRBC proportion is superior to decreased ferritin and decreased TSAT measurements for the diagnosis of iron deficiencies among renal transplant recipients.

Anemia among long-term renal transplant recipients (RTR) is not well documented (1). Even fewer data on iron status and iron deficiencies among these patients are available. In this study, we examined the prevalence of anemia and iron deficiency anemia among long-term RTR in stable condition.

Materials and Methods

All patients who visited the kidney transplant outpatient service at the University Hospital of Vienna during a period of 4 wk were included in a cross-sectional study. The patients exhibited stable graft function. Blood chemistry values were determined by using standard methods. Transferrin saturation (TSAT) was calculated as iron level/serum transferrin level x 70.9. Whole blood counts and percentages of hypochromic red blood cells (HRBC) were analyzed with a Technicon H*2 hematology analyzer (Bayer Diagnostics, Tarrytown, NY). Creatinine clearance values were calculated with the equation described by Cockcroft and Gault (2).

Independent associations with hemoglobin levels were examined in multiple stepwise regression analyses. The distribution of skewed data was normalized by natural logarithmic transformation. Logistic regression models were constructed to examine the risks (odds ratios and 95% confidence intervals) for anemia (i.e., hemoglobin levels of <12 g/dl for women and <13 g/dl for men) associated with markers of iron metabolism in the highest (HRBC) or lowest (serum ferritin levels, TSAT, serum iron levels, and serum transferrin levels) quartile of the whole patient population. To avoid multicollinearity, anemia was related to five sets of variables, in which one of five iron markers was entered. In these models, the most important predictors of hemoglobin levels (derived from the stepwise regression analyses) were also considered, i.e., creatinine clearance values below or above the median, azathioprine use (yes/no term), and polycystic kidney disease (yes/no term).

Results

The characteristics of all 438 RTR are indicated in Table 1. The proportions of patients with iron status markers within or outside the reference range are presented in Table 2. The prevalence of anemia among RTR was 39.7%. Iron deficiency was indicated by a proportion of HRBC of 2.5% for 88 patients (20.1%). The association of all variables with hemoglobin levels is presented in Table 3. Increased serum ferritin levels were associated with decreased hemoglobin concentrations. Serum transferrin levels were elevated in parallel with hemoglobin levels. The risks for anemia conferred by five markers of iron metabolism are presented in Figure 1. Among anemic or severely anemic patients, HRBC elevations were more frequent than hypoferritinemia or decreased TSAT values. The majority of patients with hemoglobin levels of <11 g/dl presented with HRBC values in the highest quartile (Table 4).

View larger version (11K): [in this window] [in a new window] [as a PowerPoint slide]   Figure 1. Markers of iron status and risk of anemia among 438 renal transplant recipients (the worst versus the other three quartiles, by logistic regression analysis). Hypochromic red blood cells (RBC): odds ratio (OR), 2.35; 95% confidence interval (CI), 1.48 to 3.75; P = 0.00029; serum transferrin level: odds ratio, 1.96; 95% confidence interval, 1.23 to 3.11; P = 0.004395; serum iron level: odds ratio, 1.56; 95% confidence interval, 0.97 to 2.49; P = 0.063608; serum ferritin level: odds ratio, 0.73; 95% confidence interval, 0.46 to 1.18; P = 0.19989; transferrin saturation (TSAT): odds ratio, 1.02; 95% confidence interval, 0.63 to 1.63; P = 0.942653.

Our study suggests that we do not attach enough importance to the diagnosis and management of anemia among RTR in stable condition. This is obviously attributable to the prevalence of unrecognized iron deficiencies, which is related to the poor information obtained from ferritin or TSAT measurements. Only 10.1% of severely anemic patients presented with serum ferritin levels of <12 µg/L, and TSAT values of <15% were observed for 29%. These results underestimate by far the number of patients with functional iron deficiencies, because HRBC values of >2.5% were detected for 46.4% and values in the upper quartile were detected for 52.2% of our severely anemic patients, reaching 64.1% among female patients. These findings strongly suggest that iron deficiencies, as diagnosed by serum ferritin or TSAT measurements, remain undetected in a significant proportion of RTR. Factors related to the prevalence of iron deficiencies may include occult blood losses, blood sampling, and adherence to a low-meat dietary regimen.

Ferritin levels may vary and may be elevated independently of iron stores in conditions such as inflammatory or infectious diseases, malignancies, or iron overload (3,4). In contrast to the negative association of serum ferritin levels with hemoglobin concentrations, C-reactive protein levels demonstrated no association with hemoglobin concentrations in our study. This finding may be attributable to immunosuppressive therapy, which was demonstrated to suppress C-reactive protein production (5). There was also a weak negative independent association of C-reactive protein with HRBC in our study population (data not shown), indicating that increases in HRBC values were not related to inflammation anemia.

In this study, a proportion of HRBC in the highest quartile substantially increased the risk for anemia, whereas decreased serum ferritin levels and decreased TSAT conferred no risk (Figure 1). Therefore, our findings support a concept in which continuous decreases in HRBC levels, even to 2%, may indicate gradual improvement of the iron supply (6,7).

A potential limitation of our study may be the lack of analysis of angiotensin I-converting enzyme (ACE) inhibition. The effect of ACE inhibition on hemoglobin levels is a matter of debate. However, the largest study reported to date clearly demonstrated that ACE inhibitor therapy did not decrease hemoglobin levels among RTR with normal hemoglobin levels (8). Another point of concern may be the lack of bone marrow examinations as the standard iron supply test. However, invasive studies are not reasonable for a large patient population.

In summary, we demonstrate that (1) anemia and iron deficiencies are under-recognized among RTR in stable condition, (2) the proportion of HRBC is the most important indicator of iron deficiencies among RTR, and (3) measurements of serum ferritin levels and TSAT are not always sufficient for the diagnosis of iron deficiencies among RTR. References.

References

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2. Cockcroft DW, Gault MH: Prediction of creatinine clearance from serum creatinine. Nephron 16: 31–41, 1976[Medline]
3. Kaltwasser JP, Gottschalk R: Erythropoietin and iron. Kidney Int 55 [Suppl 69]: S49–S56, 1999[CrossRef]
4. Miles AMV, Markell MS, Daskalakis P, Sumrani NB, Hong J, Sommer BG, Friedman EA: Anemia following renal transplantation: Erythropoietin response and iron deficiency. Clin Transplant 11: 313–315, 1997[Medline]
5. Van Lente F, Castellani W, Abbott LB: Changes in concentrations of C-reactive protein in serum after kidney or heart transplantation. Clin Chem 32: 633–636, 1986[Abstract/Free Full Text]
6. Macdougall IC, Cavill I, Hulme B, Bain B, McGregor E, McKay P, Sanders E, Coles GA, Williams JD: Detection of functional iron deficiency during erythropoietin treatment: A new approach. Br Med J 304: 225–226, 1992
7. Braun J, Lindner K, Schreiber M, Heidler RA, Hörl WH: Percentage of hypochromic red blood cells as predictor of erythropoietic and iron response after i.v. iron supplementation in maintenance haemodialysis patients. Nephrol Dial Transplant 12: 1173–1181, 1997[Abstract/Free Full Text]
8. Stigant CE, Cohen J, Vivera M, Zaltzman JS: ACE inhibitors and angiotensin II antagonists in renal transplantation: An analysis of safety and efficacy. Am J Kidney Dis 35: 58–63, 2000[Medline]
9. National Kidney Foundation–Kidney Disease Outcomes Quality Initiative (NKF-K/DOQI) Work Group: NKF-K/DOQI clinical practice guidelines for anemia of chronic kidney disease: Update 2000. Am J Kidney Dis 37 [suppl 1]: S182–S238, 2001[Medline]
10. Looker AC, Dallman PR, Carroll MD, Gunter EW, Johnson CL: Prevalence of iron deficiency in the United States. JAMA 277: 973–976, 1997[Abstract]
11. Jordan CD, Flood JG, Laposata M, Lewandrowski KB: Case records of the Massachusetts General Hospital: Weekly clinicopathological exercises: Normal reference laboratory values. Engl J Med 327: 718–724, 1992[Medline]
12. Sham RL, Raubertas RF, Braggins C, Cappuccio J, Gallagher M, Phatak PD: Asymptomatic hemochromatosis subjects: Genotypic and phenotypic profiles. Blood 96: 3707–3711, 2000[Abstract/Free Full Text]

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