Reference values for a heterogeneous ferritin assay and traceability to the 3rd International Recombinant Standard for Ferritin (NIBSC code 94/572)

Comparison of two ferritin assay platforms to assess their level of agreement in measuring serum and plasma ferritin levels in patients with chronic kidney disease

BACKGROUND

Ferritin levels are used to make decisions on therapy of iron deficiency in patients with chronic kidney disease (CKD). Hyperferritinaemia, common among patients with CKD from the Northern Territory (NT) of Australia, makes use of ferritin levels as per clinical guidelines challenging. No gold standard assay exists for measuring ferritin levels. Significant variability between results from different assays creates challenges for clinical decision-making regarding iron therapy. In the NT, different laboratories use different methods. In 2018, Territory Pathology changed the assay from Abbott ARCHITECT i1000 (AA) to Ortho-Clinical Diagnostics Vitros 7600 (OCD). This was during the planning of the INtravenous iron polymaltose for First Nations Australian patients with high FERRitin levels on haemodialysis (INFERR) clinical trial. The trial design was based on AA assay ferritin levels. We compared the two assays' level of agreement in measuring ferritin levels in CKD patients.

METHODS

Samples from INFERR clinical trial participants were analysed. Other samples from patients whose testing were completed the same day on OCD analyzers and run within 24 h on AA analyzers were added to ensure wide range of ferritin levels, adding statistical strength to the comparison. Ferritin levels from both assays were compared using Pearson's correlation, Bland-Altman, Deming and Passing-Bablok regression analyses. Differences between sample types, plasma and serum were assessed.

RESULTS

Sixty-eight and 111 (179) samples from different patients from Central Australia and Top End of Australia, respectively, were analyzed separately and in combination. The ferritin levels ranged from 3.1 µg/L to 3354 µg/L and 3 µg/L to 2170 µg/L for AA and OCD assays respectively. Using Bland-Altman, Deming and Passing-Bablok regression methods for comparison, ferritin results were consistently 36% to 44% higher with AA than OCD assays. The bias was up to 49%. AA ferritin results were the same in serum and plasma. However, OCD ferritin results were 5% higher in serum than plasma.

CONCLUSIONS

When making clinical decisions, using ferritin results from the same assay in patients with CKD is critical. If the assay is changed, it is essential to assess agreement between results from the new and old assays. Further studies to harmonize ferritin assays are required.

A Comparative Study for Measuring Serum Ferritin Levels with Three Different Laboratory Methods: Enzyme-Linked Immunosorbent Assay versus Cobas e411 and Cobas Integra 400 Methods

Different laboratory methods are used to measure serum ferritin levels as a marker of iron status in the general population. This study aimed to compare serum ferritin levels using enzyme-linked immunosorbent assay (ELISA) versus immunochemiluminescence (Cobas e411) and immunoturbidimetric (Cobas Integra 400) methods in terms of sensitivity, specificity and accuracy, and whether they can be used interchangeably. A comparative cross-sectional study enrolled one hundred and six adult Yemeni patients (33 males and 73 females) aged 18–55 years, recruited from the dermatology and cosmetic center of Hadhramout Modern Hospital, Mukalla, Yemen. Serum ferritin levels were measured using ELISA, Cobas e411, and Cobas Integra 400 methods. For method comparison, a paired-sample t-test was used. For the consistency between the three methods, they were analyzed with regression and Pearson correlation coefficient. For determining accuracy, a receiver operating curve (ROC) was used. Bias error between the methods was determined through a Bland–Altman plot analysis. Our results did not show any significant statistical difference between ELISA and Cobas e411 (52.55 ± 7.4 µg/L vs. 52.58 ± 7.5 µg/L, p = 0.967), while there were significantly higher values from Cobas Integra 400 results than Cobas e411 (56.31 ± 7.8 µg/L vs. 52.58 ± 7.5 µg/L, p < 0.001) and ELISA (52.55 ± 7.4 µg/L vs. 56.31 ± 7.8 µg/L, p < 0.001). According to the correlation coefficient and linear regression analysis, a strong association between ELISA with Cobas e411 (r = 0.993, p < 0.001) and Cobas Integra 400 results (r = 0.994, p < 0.001) were revealed. For determining accuracy, Cobas e411 and Cobas Integra 400 results showed higher sensitivity (92.0%; 90.0%) and specificity (97.7%; 99.9%) respectively. Additionally, the Bland–Altman plot analysis showed a high agreement between the ELISA and Cobas e411 methods (bias: −0.035). In contrast, there was a low agreement between the ELISA and Cobas Integra 400 methods (bias: −3.75). Similarly, the agreement between Cobas e411 and Cobas Integra 400 methods was low (bias: −3.72). Serum ferritin levels were measured by Cobas e411, and Cobas Integra 400 methods were strongly correlated with the ELISA results, with higher sensitivity, specificity, and accuracy. However, further investigations with larger samples are required for improved accuracy and more precise results, and to determine whether they can be used interchangeably.

A Comparative Study for Measuring Serum Ferritin Levels with Three Different Laboratory Methods: Enzyme-Linked Immunosorbent Assay versus Cobas e411 and Cobas Integra 400 Methods

Different laboratory methods are used to measure serum ferritin levels as a marker of iron status in the general population. This study aimed to compare serum ferritin levels using enzyme-linked immunosorbent assay (ELISA) versus immunochemiluminescence (Cobas e411) and immunoturbidimetric (Cobas Integra 400) methods in terms of sensitivity, specificity and accuracy, and whether they can be used interchangeably. A comparative cross-sectional study enrolled one hundred and six adult Yemeni patients (33 males and 73 females) aged 18–55 years, recruited from the dermatology and cosmetic center of Hadhramout Modern Hospital, Mukalla, Yemen. Serum ferritin levels were measured using ELISA, Cobas e411, and Cobas Integra 400 methods. For method comparison, a paired-sample t-test was used. For the consistency between the three methods, they were analyzed with regression and Pearson correlation coefficient. For determining accuracy, a receiver operating curve (ROC) was used. Bias error between the methods was determined through a Bland–Altman plot analysis. Our results did not show any significant statistical difference between ELISA and Cobas e411 (52.55 ± 7.4 µg/L vs. 52.58 ± 7.5 µg/L, p = 0.967), while there were significantly higher values from Cobas Integra 400 results than Cobas e411 (56.31 ± 7.8 µg/L vs. 52.58 ± 7.5 µg/L, p < 0.001) and ELISA (52.55 ± 7.4 µg/L vs. 56.31 ± 7.8 µg/L, p < 0.001). According to the correlation coefficient and linear regression analysis, a strong association between ELISA with Cobas e411 (r = 0.993, p < 0.001) and Cobas Integra 400 results (r = 0.994, p < 0.001) were revealed. For determining accuracy, Cobas e411 and Cobas Integra 400 results showed higher sensitivity (92.0%; 90.0%) and specificity (97.7%; 99.9%) respectively. Additionally, the Bland–Altman plot analysis showed a high agreement between the ELISA and Cobas e411 methods (bias: −0.035). In contrast, there was a low agreement between the ELISA and Cobas Integra 400 methods (bias: −3.75). Similarly, the agreement between Cobas e411 and Cobas Integra 400 methods was low (bias: −3.72). Serum ferritin levels were measured by Cobas e411, and Cobas Integra 400 methods were strongly correlated with the ELISA results, with higher sensitivity, specificity, and accuracy. However, further investigations with larger samples are required for improved accuracy and more precise results, and to determine whether they can be used interchangeably.

Narrative Review of Hyperferritinemia, Iron Deficiency, and the Challenges of Managing Anemia in Aboriginal and Torres Strait Islander Australians With CKD

Aboriginal and Torres Strait Islander Australians (Indigenous Australians) suffer some of the highest rates of chronic kidney disease (CKD) in the world. Among Indigenous Australians in remote areas of the Northern Territory, prevalence rates for renal replacement therapy (RRT) are up to 30 times higher than national prevalence. Anemia among patients with CKD is a common complication. Iron deficiency is one of the major causes. Iron deficiency is also one of the key causes of poor response to the mainstay of anemia therapy with erythropoiesis-stimulating agents (ESAs). Therefore, the effective management of anemia in people with CKD is largely dependent on effective identification and correction of iron deficiency. The current identification of iron deficiency in routine clinical practice is dependent on 2 surrogate markers of iron status: serum ferritin concentration and transferrin saturation (TSAT). However, questions exist regarding the use of serum ferritin concentration in people with CKD because it is an acute-phase reactant that can be raised in the context of acute and chronic inflammation. Serum ferritin concentration among Indigenous Australians receiving RRT is often markedly elevated and falls outside reference ranges within most national and international guidelines for iron therapy for people with CKD. This review explores published data on the challenges of managing anemia in Indigenous people with CKD and the need for future research on the efficacy and safety of treatment of anemia of CKD in patients with high ferritin and evidence iron deficiency.

Revising Ferritin Lower Limits: It's Time to Raise the Bar on Iron Deficiency

Ferritin is a key diagnostic marker of iron deficiency (ID), but the interpretative guidance provided to physicians varies significantly. Clear discrepancies exist between clinical guidelines that recommend evidence-based ferritin cutoffs and clinical laboratories that report highly variable ferritin reference intervals (RIs) derived from apparently healthy populations. In this study, clinical laboratories across North America were surveyed to assess the RIs provided with ferritin results. Although clinical guidelines often recommend ferritin cutoffs of 15 or 30 µg/L to identify uncomplicated ID, the survey showed that 18 of 23 responding laboratories reported female RI lower limits well below 15 µg/L. To understand the clinical impact, we analyzed 52 027 unique patient ferritin values over a 5-year period (2013-2017) from a tertiary care hospital. In this population, the 90th percentile ferritin cutoff to identify ID anemia in adults was 24 µg/L in female patients and 25 µg/L in male patients. Distribution of ferritin results in female patients showed that menopausal status had a significant effect on median values, which increased 2- to 3-fold in the postmenopausal state. Furthermore, sorting the data for female patients by physician specialty showed the highest prevalence of low ferritin values in patients seen in obstetrics and gynecology. This study highlights the discrepancy between clinical guidelines and clinical laboratory practice for ferritin reporting and indicates that ferritin RIs, particularly for female patients, are set to an inappropriately low threshold in most clinical laboratories in North America; this level provides good specificity but poor sensitivity when screening for ID.

Performance and comparability of laboratory methods for measuring ferritin concentrations in human serum or plasma: A systematic review and meta-analysis

BACKGROUND

Different laboratory methods are used to quantify ferritin concentrations as a marker of iron status. A systematic review was undertaken to assess the accuracy and comparability of the most used methods for ferritin detection.

METHODS AND FINDINGS

National and regional databases were searched for prospective, retrospective, sectional, longitudinal and case-control studies containing the characteristics and performance of at least one method for serum/plasma ferritin determinations in humans published to date. The analysis included the comparison between at least 2 methods detailing: sensitivity, precision, accuracy, predictive values, inter-methods adjustment, and use of international reference materials. Pooled method performance was analyzed for each method and across methods.

OUTCOMES

Search strategy identified 11893 records. After de-duplication and screening 252 studies were assessed, including 187 studies in the qualitative analysis and 148 in the meta-analysis. The most used methods included radiometric, nonradiometric and agglutination assays. The overall within-run imprecision for the most reported ferritin methods was 6.2±3.4% (CI 5.69-6.70%; n = 171), between-run imprecision 8.9±8.7% (CI 7.44-10.35%; n = 136), and recovery rate 95.6% (CI 91.5-99.7%; n = 94). The pooled regression coefficient was 0.985 among all methods analyzed, and 0.984 when comparing nonradiometric and radiometric methods, without statistical differences in ferritin concentration ranging from 2.3 to 1454 μμg/L.

CONCLUSION

The laboratory methods most used to determine ferritin concentrations have comparable accuracy and performance. Registered in PROSPERO CRD42016036222.