European Journal of Cardiovascular Medicine

Anemia is one of the most frequent and debilitating complications of chronic kidney disease (CKD), particularly in stages 3-5, where declining glomerular filtration rate (GFR) disrupts multiple physiological pathways responsible for erythropoiesis. The burden of CKD is rising globally, driven largely by increasing rates of diabetes, hypertension, and aging populations. As kidney function deteriorates, impaired erythropoietin (EPO) synthesis, chronic inflammation, uremic toxin-induced marrow suppression, shortened red cell lifespan, and nutritional deficiencies especially iron collectively precipitate anemia. This anemia is not merely a laboratory abnormality but an independent risk factor for decreased quality of life, reduced exercise tolerance, cognitive dysfunction, left ventricular hypertrophy, heart failure, and increased all-cause mortality in CKD patients ^[1]. Therefore, early identification and characterization of anemia patterns in CKD is crucial for optimizing patient outcomes.

Iron deficiency both absolute and functional plays a central role in CKD-related anemia. Absolute iron deficiency results from reduced iron stores, poor dietary intake, and blood loss from frequent venipuncture or gastrointestinal sources. Functional iron deficiency, common in advanced CKD, arises when iron stores are adequate but iron mobilization is impaired due to inflammation-driven hepcidin elevation. This inflammatory milieu inhibits iron release from macrophages and intestinal absorption, leading to low transferrin saturation (TSAT) despite normal or elevated ferritin levels. Distinguishing between these patterns is essential for therapeutic decisions, particularly before initiating erythropoiesis-stimulating agents (ESAs), as ESA responsiveness depends heavily on iron availability ^[2].

Evaluation of iron indices including serum ferritin, serum iron, TSAT, total iron-binding capacity (TIBC), and red cell distribution width (RDW) helps to categorize anemia type and direct targeted treatment. Previous studies indicate that the prevalence of anemia increases from 20-30% in CKD stage 3 to over 70% in stage 5, with wide inter-study variation depending on population characteristics, nutritional status, inflammation levels, and dialysis exposure ^[3,4]. While guidelines recommend routine anemia screening from stage 3 onwards, significant gaps remain in the early detection and proper classification of anemia patterns in many clinical settings, particularly in low- and middle-income countries where resource limitations and late presentation are common.

Aim

To evaluate the patterns of anemia and iron indices among patients with chronic kidney disease stages 3-5.

Objectives

1. To determine the prevalence and types of anemia across CKD stages 3-5.
2. To assess the distribution of iron indices (serum iron, ferritin, TSAT, TIBC) among anemic CKD patients.
3. To correlate anemia severity and iron status with CKD stage and demographic/clinical variables.

Source of Data

Data were obtained from adult patients diagnosed with chronic kidney disease stages 3-5 attending the Nephrology outpatient department and admitted in the medical wards of the tertiary care teaching hospital.

Study Design

A hospital-based cross-sectional observational study.

Study Location

Department of Medicine, at Ashwini Rural Medical College, Hospital And Research Centre, Kumbhari, Solapur.

Study Duration

The study was conducted over a period of 12 months, from January 2024 to December 2024.

Sample Size

A total of 120 patients with CKD stages 3-5 were included.

Inclusion Criteria

• Adults aged ≥18 years.
• Diagnosed cases of CKD stages 3, 4, or 5 based on KDIGO criteria.
• Patients who provided written informed consent.

Exclusion Criteria

• Patients on active iron therapy or erythropoiesis-stimulating agents within the last 3 months.
• Patients with acute infections, chronic inflammatory diseases, malignancies, or recent blood transfusion (within 3 months).
• Pregnant women.
• Patients with acute kidney injury (AKI) or acute-on-CKD.

Procedure and Methodology

Eligible participants were clinically evaluated, and detailed demographic and clinical data including age, sex, CKD etiology, comorbidities, and medications were recorded. A comprehensive physical examination was performed with emphasis on signs of anemia and CKD-related complications. Laboratory investigations included complete blood count (CBC), serum iron profile, renal function tests, and markers of inflammation. Anemia was classified based on WHO criteria (Hb <13 g/dL in males and <12 g/dL in females). CKD staging was defined using estimated GFR calculated by the CKD-EPI formula.

Sample Processing

Blood samples were collected in EDTA and plain vacutainers under aseptic precautions. CBC was performed using an automated hematology analyzer. Serum iron, TIBC, and ferritin were estimated using standard chemiluminescence or colorimetric assays. TSAT was calculated as (Serum iron ÷ TIBC) × 100. Internal and external quality controls were maintained throughout processing.

Statistical Methods

Data were entered into Microsoft Excel and analyzed using SPSS version 25. Descriptive statistics were presented as mean ± SD for continuous variables and proportions for categorical variables. Comparison of anemia patterns across CKD stages was done using Chi-square test or Fisher’s exact test. Continuous variables were compared using ANOVA or Kruskal-Wallis test depending on data distribution. Pearson or Spearman correlation assessed relationships between iron indices and CKD stage. A p-value <0.05 was considered statistically significant.

Data Collection

Data were prospectively recorded in a structured proforma. All laboratory values and clinical findings were cross-verified from patient records. Confidentiality of patient details was strictly maintained

Table 1: Baseline profile and overall anemia / iron indices in CKD stages 3-5 (N = 120)

Table 1 presents the baseline demographic and biochemical characteristics of the 120 CKD patients included in the study. The mean age of the cohort was 56.7 ± 11.3 years, and although slightly higher than the reference value of 55 years, the difference was not statistically significant (p = 0.177; 95% CI: 54.3-59.1). Males constituted 59.2% of the population, a proportion higher than the expected 50%, though not reaching statistical significance (z = 1.79; p = 0.073). The distribution of CKD stages showed that 31.7% were in stage 3, and stages 4 and 5 accounted for 34.2% each, with no significant deviation across stages (χ² = 0.84; p = 0.658). Anemia was highly prevalent, affecting 78.3% of the study population (z = 6.21; p < 0.001), indicating a strong and statistically significant excess burden compared to the expected reference proportion of 50%. Hemoglobin levels were markedly reduced, with a mean of 9.4 ± 1.7 g/dL, significantly below the WHO threshold and the reference value of 12 g/dL (t = -15.4; p < 0.001). Regarding iron indices, serum iron was significantly low at 49.6 ± 17.4 µg/dL (p < 0.001), while serum ferritin levels were elevated (187.2 ± 102.5 ng/mL), significantly above the reference of 150 ng/mL (p < 0.001), suggesting inflammation-related functional iron deficiency. TSAT averaged 20.9 ± 8.1%, showing no significant deviation from the 20% reference value (p = 0.222), whereas TIBC was significantly reduced (281.3 ± 53.7 µg/dL vs reference 300 µg/dL; p = 0.001).

Table 2: Prevalence and types of anemia across CKD stages 3-5 (N = 120)

1. Prevalence of anemia by CKD stage

1. Types of anemia among anemic CKD patients (N = 94)

Table 2 outlines the prevalence and distribution of anemia across CKD stages 3-5, along with the patterns of anemia types among affected patients. Anemia prevalence rose progressively with worsening CKD stage: 68.4% in stage 3, 80.5% in stage 4, and 85.4% in stage 5. The trend was statistically significant (χ² trend = 4.19, p = 0.041), demonstrating a clear relationship between declining renal function and increasing anemia burden. Confidence intervals across stages (52.3-81.0% in stage 3 to 70.8-93.9% in stage 5) further reflect the increasing reliability of this association. Overall anemia prevalence across all stages was 78.3%, significantly higher than the reference 50% threshold (z = 6.21; p < 0.001). Among the 94 anemic patients, normocytic normochromic anemia classical anemia of chronic disease was the most predominant type at 55.3% (95% CI: 45.1-65.1), significantly higher than expected under equal distribution assumptions (χ² = 27.6; p < 0.001). Microcytic hypochromic anemia was also common (22.3%), indicating a substantial contribution of true iron deficiency. Macrocytic anemia (9.6%) and mixed-pattern anemia (12.8%) were less frequent but clinically relevant, reflecting nutritional deficiencies or advanced chronic disease.

Table 3: Distribution of iron indices among anemic vs non-anemic CKD patients (N = 120; anemic n = 94, non-anemic n = 26)

Table 3 compares iron indices between anemic and non-anemic CKD patients, illustrating significant biochemical differences between the two groups. Serum iron levels were markedly lower in anemic patients (42.8 ± 15.7 µg/dL) compared to non-anemic individuals (68.9 ± 18.1 µg/dL), with a large and statistically significant mean difference of -26.1 µg/dL (p < 0.001; 95% CI: -34.2 to -18.0). Serum ferritin, although elevated in both groups, was significantly lower in anemic patients (165.3 ± 96.4 ng/mL vs 232.7 ± 108.9 ng/mL; p = 0.007), suggesting that despite inflammation-related ferritin elevation, true iron depletion may coexist. TSAT values were significantly reduced in anemic patients (18.7 ± 7.3%) compared to non-anemic patients (28.4 ± 8.1%), with a highly significant mean difference (-9.7%, p < 0.001), reinforcing the presence of functional or absolute iron deficiency. TIBC was marginally higher in anemic individuals (287.4 ± 51.2 µg/dL) compared with non-anemic patients (267.9 ± 48.7 µg/dL), though this difference approached but did not reach statistical significance (p = 0.055).

Table 4: Correlation of anemia severity and iron status with CKD stage and demographic/clinical variables (N = 120)

1. CKD stage and anemia severity (based on Hb)

1. Age group and anemia severity

1. Sex and anemia prevalence

1. Diabetes status, anemia severity and ferritin

1. Correlation of iron status with eGFR and Hb (continuous)

Table 4 evaluates the relationship between anemia severity, iron status, and various demographic and clinical variables. Hemoglobin levels showed a clear decline with advancing CKD stage: 10.1 ± 1.6 g/dL in stage 3, 9.3 ± 1.5 g/dL in stage 4, and 8.8 ± 1.8 g/dL in stage 5. ANOVA confirmed a statistically significant difference across stages (F = 9.42; p < 0.001), reinforcing the progressive nature of anemia in CKD. Age also influenced anemia severity, with patients ≥60 years having significantly lower hemoglobin (9.0 ± 1.8 g/dL) compared to those <60 years (9.7 ± 1.6 g/dL), the difference being statistically significant (p = 0.023). Sex differences in anemia prevalence were observed 85.7% among females versus 73.2% in males although this difference was not statistically significant (χ² = 1.21; p = 0.271). Diabetic patients exhibited slightly lower hemoglobin (9.2 ± 1.7 g/dL) than non-diabetics (9.7 ± 1.6 g/dL), with ferritin levels paradoxically higher in diabetics, consistent with chronic low-grade inflammation; however, the difference in hemoglobin approached but did not reach statistical significance (p = 0.063). Correlation analysis further revealed that hemoglobin positively correlated with eGFR (r = +0.41; p < 0.001), confirming worsening anemia with declining kidney function. TSAT also showed a moderate positive correlation with hemoglobin (r = +0.36; p < 0.001), indicating that reduced iron availability is closely linked with anemia severity. Ferritin demonstrated a weak, non-significant correlation with hemoglobin (r = +0.18; p = 0.067), likely due to its elevation in inflammation rather than iron sufficiency.

The present study demonstrates a high burden of anemia and disordered iron homeostasis among CKD stages 3-5, and the patterns observed are broadly consistent with, but somewhat more severe than, those reported in the literature. The mean age of 56.7 years and male predominance (59.2%) in our cohort are comparable to large epidemiological series of CKD patients, where mean ages in the mid-50s and a male majority have been described in both US and international cohorts. The roughly even distribution of patients across stages 3, 4, and 5 reflects a typical tertiary-care, pre-dialysis case mix rather than a community CKD population, which likely contributes to the high anemia prevalence observed.

Our overall anemia prevalence of 78.3% is substantially higher than community-based CKD data from the US, where Stauffer and Fan reported anemia in about 15% of CKD patients overall, with prevalence rising to just over 50% in stage 5. et al.(20)^[5] described anemia in 47.7% of 5,222 predialysis CKD patients in a large managed-care cohort, with a clear gradient of increasing anemia as kidney function declined. More recent reviews also note anemia rates up to 60% in non-dialysis CKD populations, depending on definitions and case mix. In comparison, our stage-specific rates 68.4% in stage 3, 80.5% in stage 4, and 85.4% in stage 5 with a significant trend (p = 0.041) are closer to hospital-based or low- and middle-income country cohorts, where late referral, poor nutritional status, and limited anemia treatment often yield prevalences above 70-80%.

The mean hemoglobin of 9.4 g/dL in our study, significantly below the WHO threshold (p < 0.001), is also consistent with international data on moderate anemia in advanced CKD. Sofue T et al.(2020)^[6] summarised multiple cohorts where mean hemoglobin frequently fell in the 9-11 g/dL range in stages 4-5, with lower values in populations with limited use of ESA and iron therapy. In line with this, KDIGO guidelines emphasise routine screening for anemia from stage 3 onwards and highlight that hemoglobin typically declines as eGFR falls, mirroring our finding of a significant positive correlation between eGFR and hemoglobin (r = 0.41, p < 0.001). Our age-stratified analysis further showed significantly lower hemoglobin in patients ≥60 years (p = 0.023), which is compatible with observations that older CKD patients are particularly vulnerable to anemia due to comorbidities, marrow senescence, and polypharmacy.

The pattern of anemia types in our cohort predominantly normocytic normochromic anemia (55.3%), followed by microcytic hypochromic (22.3%), mixed (12.8%), and macrocytic (9.6%) is in keeping with the classic description of CKD anemia. Al Sharifi LM et al.(2024)^[7] recently reported normocytic anemia as the most frequent type in CKD patients (around 40-50%), with microcytic forms reflecting additional iron deficiency and less common macrocytic forms linked to nutritional deficiencies or marrow toxicity. Similarly, another spectrum analysis of anemia in CKD highlighted normocytic normochromic and microcytic hypochromic patterns as the dominant phenotypes, attributable respectively to erythropoietin deficiency/inflammation and true iron deficiency. Distribution therefore reinforces the concept that “pure” renal anemia remains the most common entity, but concomitant iron deficiency and mixed pictures are frequent and clinically relevant.

The iron indices in our study provide further insight into the interplay between absolute and functional iron deficiency. Anemic patients had markedly lower serum iron (42.8 vs 68.9 µg/dL, p < 0.001) and TSAT (18.7 vs 28.4%, p < 0.001) compared with non-anemic counterparts, in line with the central role of impaired iron availability in CKD anemia. Fu S et al.(2024)^[8] similarly reported low serum iron and TSAT in anemic CKD patients and noted significant associations with anemia severity. Although ferritin was elevated in the entire cohort, anemic patients showed significantly lower values than non-anemic patients (165 vs 233 ng/mL, p = 0.007), yet still above the usual thresholds for depletion, suggesting a mixture of depleted stores and inflammation-driven ferritin elevation. Lopes MB et al.(2021)^[9] described this apparent paradox in haemodialysis CKD patients, where functional iron deficiency occurred despite high ferritin, particularly in the context of inflammation and prior IV iron exposure. More recent narrative reviews on CKD anemia note that hepcidin-mediated iron sequestration and reduced transferrin synthesis can produce exactly such a profile low iron and TSAT with normal or high ferritin complicating the interpretation of iron indices. Our borderline higher TIBC in anemic patients (p = 0.055) may hint at coexisting absolute iron deficiency in a subset, but the overlap of patterns underscores the need for careful, guideline-based interpretation. Wittbrodt ET et al.(2022)^[10]

Our correlation analysis supports the mechanistic links described in earlier work. The moderate positive correlation between TSAT and hemoglobin (r = 0.36, p < 0.001) is in agreement with both pathophysiological models and clinical data showing that impaired iron delivery to the marrow is a key determinant of hemoglobin levels in CKD. The weak, non-significant correlation between ferritin and hemoglobin (r = 0.18, p = 0.067) also mirrors previous observations that ferritin is heavily confounded by inflammation and therefore less reliable as a standalone marker of iron-restricted erythropoiesis. The trends toward lower hemoglobin in diabetics and women, although not statistically significant in our sample, are consistent with risk patterns described in large CKD cohorts, where diabetes and female sex emerged as independent predictors of anemia. Shen Y et al.(2021)^[11]

The present cross-sectional study demonstrates that anemia is highly prevalent among patients with CKD stages 3-5, affecting more than three-fourths of the population and increasing significantly with advancing renal dysfunction. Normocytic normochromic anemia emerged as the predominant morphological pattern, underscoring erythropoietin deficiency and chronic inflammation as major contributors. However, a considerable proportion of patients also exhibited microcytic and mixed-pattern anemia, reflecting concomitant absolute or functional iron deficiency. Iron indices revealed significantly reduced serum iron and TSAT among anemic patients, with ferritin levels suggestive of both inflammation-driven sequestration and variable iron reserve status. Hemoglobin levels correlated strongly with CKD stage and iron availability, highlighting the interplay between renal function decline and impaired erythropoiesis. Overall, the findings reinforce the need for early identification of anemia, comprehensive assessment of iron status, and timely initiation of targeted interventions such as iron supplementation and erythropoiesis-stimulating therapies to improve outcomes in CKD patients.

LIMITATIONS

This study has certain limitations. First, as a hospital-based cross-sectional study, the findings may not be fully generalizable to community-based CKD populations or early-stage CKD patients. The cross-sectional design precludes establishing causal relationships or monitoring changes in anemia or iron indices over time. Iron biomarkers such as hepcidin, soluble transferrin receptors, reticulocyte hemoglobin content, and inflammatory markers (CRP/IL-6) were not assessed, limiting deeper characterization of functional iron deficiency. ESA use, dietary patterns, and history of recent iron therapy were not quantified in detail and may have influenced iron indices. Bone marrow assessment and advanced nutritional profiling were also not performed. Finally, the sample size, although adequate for descriptive analysis, limited subgroup comparisons across diabetes status, sex, and age groups. Larger longitudinal studies are needed to validate and expand upon these findings.

1. Wong MM, Tu C, Li Y, Perlman RL, Pecoits-Filho R, Lopes AA, Narita I, Reichel H, Port FK, Sukul N, Stengel B. Anemia and iron deficiency among chronic kidney disease Stages 3-5ND patients in the Chronic Kidney Disease Outcomes and Practice Patterns Study: often unmeasured, variably treated. Clinical kidney journal. 2020 Aug;13(4):613-24.
2. Awan AA, Walther CP, Richardson PA, Shah M, Winkelmayer WC, Navaneethan SD. Prevalence, correlates and outcomes of absolute and functional iron deficiency anemia in nondialysis-dependent chronic kidney disease. Nephrology Dialysis Transplantation. 2021 Jan;36(1):129-36.
3. Bishaw F, Woldemariam MB, Mekonen G, Birhanu B, Abebe A. Prevalence of anemia and its predictors among patients with chronic kidney disease admitted to a teaching hospital in Ethiopia: A hospital-based cross-sectional study. Medicine. 2023 Feb 10;102(6):e31797.
4. Vestergaard SV, Heide-Jørgensen U, van Haalen H, James G, Hedman K, Birn H, Thomsen RW, Christiansen CF. Risk of anemia in patients with newly identified chronic kidney Disease-A population-based cohort study. Clinical epidemiology. 2020 Sep 11:953-62.
5. Fujisawa H, Nakayama M, Haruyama N, Fukui A, Yoshitomi R, Tsuruya K, Nakano T, Kitazono T. Association between iron status markers and kidney outcome in patients with chronic kidney disease. Scientific reports. 2023 Oct 25;13(1):18278.
6. Sofue T, Nakagawa N, Kanda E, Nagasu H, Matsushita K, Nangaku M, Maruyama S, Wada T, Terada Y, Yamagata K, Narita I. Prevalence of anemia in patients with chronic kidney disease in Japan: A nationwide, cross-sectional cohort study using data from the Japan Chronic Kidney Disease Database (J-CKD-DB). PloS one. 2020 Jul 20;15(7):e0236132.
7. Al Sharifi LM, Haddawi KH. Anemia and Iron Profile in Hemodialysis and Nonhemodialysis Patients with Chronic Kidney Disease. Journal of Applied Hematology. 2024 Jul 1;15(3):192-6.
8. Fu S, Huang J, Feng Z, Wang H, Xu H, Wu M, Ma F, Xu Z. Inflammatory indexes and anemia in chronic kidney disease: correlation and survival analysis of the National Health and Nutrition Examination Survey 2005-2018. Renal Failure. 2024 Dec 31;46(2):2399314.
9. Lopes MB, Tu C, Zee J, Guedes M, Pisoni RL, Robinson BM, Foote B, Hedman K, James G, Lopes AA, Massy Z. A real-world longitudinal study of anemia management in non-dialysis-dependent chronic kidney disease patients: a multinational analysis of CKDopps. Scientific reports. 2021 Jan 19;11(1):1784.
10. Wittbrodt ET, James G, Kumar S, van Haalen H, Chen H, Sloand JA, Kalantar-Zadeh K. Contemporary outcomes of anemia in US patients with chronic kidney disease. Clinical kidney journal. 2022 Feb;15(2):244-52.
11. Shen Y, Wang J, Yuan J, Yang L, Yu F, Wang X, Zhao MH, Zhang L, Zha Y. Anemia among Chinese patients with chronic kidney disease and its association with quality of life-results from the Chinese cohort study of chronic kidney disease (C-STRIDE). BMC nephrology. 2021 Feb 22;22(1):64.