Susceptibility of commonly used ferritin assays to the classic hook effect

Data-driven quality assurance to prevent erroneous test results

Increasing laboratory automation and efficiency requires quality assurance (QA) approaches to ensure that reported results are precise and accurate. Prerequisites for designing optimal QA strategies include an in-depth understanding of the laboratory processes, the expected results, and of the mechanisms that can cause erroneous results. Oftentimes, a laboratory's own data, extracted from the laboratory information system, electronic medical record, and/or clinical data warehouse are necessary to master the aforementioned requirements. Data-driven QA utilizes retrospective and/or prospective laboratory results to minimize errors in the clinical laboratory due to pre-analytical or analytical vulnerabilities. Additionally, exploitation of this data may improve result interpretation. The objective of this review is to illustrate specific examples of data-driven QA approaches for several areas of the clinical laboratory and for different phases of the testing cycle.

Falsely decreased ferritin concentrations in two patients with haemophagocytic lymphohistiocytosis: A case report

The high-dose hook effect, or prozone effect, can lead to negative or falsely lowered plasma ferritin results. Here, cases of a 16-year-old boy and a 70-year-old woman with haemophagocytic lymphohystiocytosis with extremely high concentrations of plasma ferritin (387,000 μg/L and 138,000 μg/L, respectively) are presented. In both cases, falsely lowered ferritin results were reported without any analyser flag. This article emphasizes the importance of recognition of the high-dose hook effect, since a watertight solution is lacking.

High-dose HOOK effect in urinary DcR2 assay in patients with chronic kidney disease

BACKGROUND

Urinary DcR2 (uDcR2) is a biomarker for the early detection the tubulointerstitial injury (TII) in patients with chronic kidney disease (CKD), but the high-dose hook effect may lead to falsely low or even negative results when using an enzyme-linked immunosorbent assay (ELISA). This study aimed to investigate if the high-dose hook effect exists with ELISA testing, and to uncover a potential approach for reducing this effect.

METHODS

72 CKD patients were recruited and categorized into four groups based on TII scores. uDcR2 was measured in undiluted and serially diluted (two-, four-, eight- and 16-fold dilutions) urine using an ELISA kit. The results from the assay were normalized to urinary creatinine. We evaluated the correlation between uDcR2/cre levels at different dilutions and renal histological parameters. Receiver operating characteristic (ROC) curves were generated to examine the value of uDcR2/cre for predicting TII.

RESULTS

uDcR2/cre levels in the undiluted urine were significantly higher in patients with CKD than those in the control. However, higher TII scores did not yield higher levels of uDcR2/cre in the undiluted urine. After serial dilution, uDcR2/cre levels were highest with the four-fold dilution. A positive correlation was found between uDcR2/cre levels at different dilutions and TII scores, with the highest correlation coefficient and the largest AUC being observed at the four-fold dilution.

CONCLUSIONS

The high-dose hook effect was apparent during ELISA testing of uDcR2 in CKD patients, yet dilution of the urine samples neutralized this effect. However, the use of a four-fold dilution of urine for uDcR2/cre testing may eliminate the high-dose hook effect and make it possible to effectively monitor the severity of TII in CKD patients.

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.

Upfront dilution of ferritin samples to reduce hook effect, improve turnaround time and reduce costs

Introduction

Sandwich immunoassays offer advantages in the clinical laboratory but can yield erroneously low results due to hook (prozone) effect, especially with analytes whose concentrations span several orders of magnitude such as ferritin. This study investigated a new approach to reduce the likelihood of hook effect in ferritin immunoassays by performing upfront, five-fold dilutions of all samples for ferritin analysis. The impact of this change on turnaround time and costs were also investigated.

Materials and methods

Ferritin concentrations were analysed in routine clinical practice with and without upfront dilutions on Siemens Centaur® XP (Siemens Healthineers, Erlang, Germany) immunoanalysers. In addition, one month of baseline data (1026 results) were collected prior to implementing upfront dilutions and one month of data (1033 results) were collected after implementation.

Results

Without upfront dilutions, hook effect was observed in samples with ferritin concentrations as low as 86,028 µg/L. With upfront dilutions, samples with ferritin concentrations as high as 126,050 µg/L yielded values greater than the measurement interval and would have been diluted until an accurate value was obtained. The implementation of upfront dilution of ferritin samples led to a decrease in turnaround time from a median of 2 hours and 3 minutes to 1 hour and 18 minutes (P = 0.002).

Conclusions

Implementation of upfront dilutions of all ferritin samples reduced the possibility of hook effect, improved turnaround time and saved the cost of performing additional dilutions.