Shift happens: the utility of external quality assessment data in evaluating folate lot changes

Rachel Marrington; Sarah L. Davies; Finlay MacKenzie

doi:10.1515/cclm-2025-1569

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Shift happens: the utility of external quality assessment data in evaluating folate lot changes

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Published/Copyright: December 11, 2025

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From the journal Clinical Chemistry and Laboratory Medicine (CCLM) Volume 64 Issue 4

Keywords: folate; lot-to-lot; EQA

To the Editor,

We welcomed the letter by Larsson et al. on the recent decline in patient serum folate test levels using Roche Diagnostics Folate III assay [1]. The use of patient medians is a highly valuable tool which can be used as part of the laboratory’s toolkit for managing risk [2].

External Quality Assessment (EQA) data is another valuable tool within that toolkit [3] and it remains vibrant. However, at present the quality framework within the United Kingdom (UK) has missing or disjointed elements with barriers to connecting manufacturer, laboratory, EQA and clinical outcome data [4]. We strongly believe that this is not conducive for patient safety. Greater data transparency and open collaboration between all stakeholders is required to improve analytical and clinical assay performance, and a safe space must be created for this.

In this spirit, we would like to provide data from our UK NEQAS for Haematinics EQA Scheme to corroborate initial observations by Larsson et al. We have already shared this with our registered participants and the manufacturer concerned. However, we feel that it is important to give all laboratories a more complete evidence base to inform their clinical risk management of the folate Lot shifts. This is by no means an isolated Lot shift; within our extensive EQA scheme repertoire there are examples from all major manufacturers of deliberate or unintentional Lot shifts that laboratories will be managing. We have selected folate merely as an opportunistic example to demonstrate the utility of EQA data as an adjunct to available clinical data [1]. We could just as easily select other measurands from other manufacturers.

The UK NEQAS for Haematinics Assays EQA Scheme provides three liquid specimens on a monthly basis to UK and international participants [5]. Pooled serum based on folate concentration from same-sex donor is predominantly used. A stabiliser is added to ensure stability of folate levels. The main part of the EQA scoring process is an assessment of bias on each specimen, which in turn is then averaged over a six-distribution time window to give a B score (Bias score). Figure 1 shows box and whisker plots of B scores for the Roche folate assay from May 2020 (Distribution 271) to November 2025 (Distribution 331). This clearly demonstrates the decreasing negative bias in the Roche folate assay emerging since September 2024 (Distribution 319). Our Roche data is not broken down by the E1 or E2 reagent. According to Larsson et al. the Roche Folate III reagent was released in October 2023 [1]; however, it does appear to have taken a number of months before this reagent was fully in use in the UK.

Figure 1:

‘Seismograph plot’ – Box and Whisker trend plot bias (B scores) for Roche folate from May 2020 (Distribution 271) to November 2025 (Distribution 331). The B score is the average of 18 specimen biases over a rolling six-month time window.

Although our default position is to use an All Laboratory Trimmed Mean (ALTM) as the Target value for folate, from September 2024 (Distribution 319) we removed all Roche folate results because the target was being skewed. Because we routinely distribute repeated material over short and long timescales as part of our post-market surveillance of assay performance, we could clearly see from review of repeat distributions of the same material we demonstrated this was a genuine change in the Roche folate assay only, and was not observed for other manufacturers. We discussed this with Roche.

Clinical interpretation must be considered in the context of folate assay reformulation [6]. Within our UK NEQAS for Haematinics Assays EQA Scheme, we also evaluate clinical interpretation of results and regularly capture reference interval data. We ask participants to categorise the numerical results as either ‘Low’, ‘Indeterminate’, ‘Normal’ or 'High' as indicated by their respective reference intervals. Our data is showing clearly the impact from the negative bias from the Roche folate assay on result interpretation, which would then subsequently impact patient management.

Figure 2 shows the data from October 2025 – Distribution 331. The specimens at Distribution 331 were three pools of unmanipulated pooled serum (other than the addition of a stabiliser). The ALTMs for each specimen were 4.00 ug/L, 4.56 ug/L and 8.20 ug/L respectively. Roche results are presented by their Lot number. In total 422 folate results were returned by Participants at this distribution, with 40 % being from Roche. Lot numbers for reagent and calibrators were provided by 87 % of Roche users. For all specimens the Roche method means, by Lot number, are less than the ALTM (red dashed line). However, on closer inspection of the data there appears to be a contemporaneous concentration dependent bias between the ‘new Lot numbers’ (taking 911203 as a representation) and ‘existing Lot’ (for example 872557). This is a dynamic situation, so this data is merely a single snapshot.

Figure 2:

Ranked data for Roche folate results, by reagent lot number, at Distribution 331. The red dashed lines are the ALTM for each specimen. (A) Specimen 331A [ALTM=4.00 ug/L], (B) specimen 331B [ALTM=4.56 ug/L] and (C) specimen 331C [ALTM=8.20 ug/L].

We find calibrator and reagent Lot number information an invaluable tool for supporting troubleshooting. Currently, participants must manually provide these data and then we have to manually data-cleanse these data for interrogation which is cumbersome. Many global health systems are prioritising digital pathology, with the National Health Service 10-year plan being our local mandate [7]. Automated connectivity and inter-operability of laboratory data, including Lot number information, is highly desirable for post-market surveillance of analytical performance. Facilitating safe sharing of clinical data between laboratories, manufacturers and EQA providers is important for assessing the true clinical impact of Lot changes. Moreover, we need more clearly defined consensus Analytical Performance Specifications for Lot shifts which manufacturers, laboratories and EQA providers can consistently use to detect deterioration in assay performance. Some guidance [8] and literature precedence exists, notably including characterisation of acceptable Lot-to-Lot variation around the 99th percentile clinical decision threshold for high-sensitivity cardiac troponins [9]. We support professional laboratory medicine societies within the UK, and any other interested party, who are working in this area; defining a performance concern is the necessary first step to resolving any issues arising. Whilst different stakeholders are developing criteria in isolation there will undoubtedly be heterogeneity.

The current response is reactive. Greater utilisation of EQA and clinical data during pre-market evaluation of new Lot numbers by manufacturers may be another area where we could collectively develop a more pro-active system for detecting issues prior to Lot distribution to laboratories.

The data within our UK NEQAS for Haematinics Assays Scheme strongly supports the findings by Larsson et al. in that there has been a change in performance of Roche folate assays [1] which are not giving comparable folate results to other manufacturers. Our reagent Lot information shows the importance of capturing and monitoring Lot information. Our clinical interpretive data reinforces the importance of clinical context, which can only be completely understood when there is genuine transparency and collaboration between manufacturers, laboratories, EQA providers and the clinicians using the tests to manage patients. The principles exemplified with these data hold true for all analytes and manufacturers. With great data, comes great responsibility. We have a collective responsibility to start using this data more effectively to ensure that we are getting it right for the patient.

Corresponding author: Rachel Marrington, Birmingham Quality (UK NEQAS), University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK, E-mail: rachel.marrington@uhb.nhs.uk

Research ethics: Not applicable.
Informed consent: Not applicable.
Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission.
Use of Large Language Models, AI and Machine Learning Tools: None declared.
Conflict of interest: The authors state no conflict of interest.
Research funding: None declared.
Data availability: Not applicable.

References

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Received: 2025-11-24

Accepted: 2025-11-26

Published Online: 2025-12-11

Published in Print: 2026-03-26

This work is licensed under the Creative Commons Attribution 4.0 International License.

Articles in the same Issue

https://doi.org/10.1515/cclm-2025-1569

Keywords for this article

folate; lot-to-lot; EQA

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