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Table of Contents for Annals of Clinical Biochemistry. List of articles from both the latest and ahead of print issues.
Updated: 15 min 15 sec ago

Can artificial intelligence replace biochemists? A study comparing interpretation of thyroid function test results by ChatGPT and Google Bard to practising biochemists

Wed, 09/20/2023 - 10:50
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundPublic awareness of artificial intelligence (AI) is increasing and this novel technology is being used for a range of everyday tasks and more specialist clinical applications. On a background of increasing waits for GP appointments alongside patient access to laboratory test results through the NHS app, this study aimed to assess the accuracy and safety of two AI tools, ChatGPT and Google Bard, in providing interpretation of thyroid function test results as if posed by laboratory scientists or patients.MethodsFifteen fictional cases were presented to a team of clinicians and clinical scientists to produce a consensus opinion. The cases were then presented to ChatGPT and Google Bard as though from healthcare providers and from patients. The responses were categorized as correct, partially correct or incorrect compared to consensus opinion and the advice assessed for safety to patients.ResultsOf the 15 cases presented, ChatGPT and Google Bard correctly interpreted only 33.3% and 20.0% of cases, respectively. When queries were posed as a patient, 66.7% of ChatGPT responses were safe compared to 60.0% of Google Bard responses. Both AI tools were able to identify primary hypothyroidism and hyperthyroidism but failed to identify subclinical presentations, non-thyroidal illness or secondary hypothyroidism.ConclusionsThis study has demonstrated that AI tools do not currently have the capacity to generate consistently correct interpretation and safe advice to patients and should not be used as an alternative to a consultation with a qualified medical professional. Available AI in its current form cannot replace human clinical knowledge in this scenario.

Paediatric reference ranges for plasma chromogranin A

Fri, 09/15/2023 - 02:15
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundNeuroendocrine neoplasms (NENs) are a heterogeneous group of rare diseases with varied aggressiveness originating from endocrine cells belonging to the diffuse endocrine system and most often produce and secrete chromogranin A (CgA). CgA in plasma is therefore used to screen, diagnose, and monitor for NENs in both adults and children with sporadic or familial NENs.MethodsPlasma CgA was measured using the Brahms Kryptor assay in 268 healthy children/adolescents; 85 children were tested as part of a familial cancer screening program and 183 additional children younger than 20 years of age underwent screening for allergies. Repeated measurements (month – years) was used to calculate the intra-individual variation. The dataset was analysed in R using the referenceInterval package.ResultsThe plasma CgA concentration decreased with age and was 32–118 µg/L for children aged 0–3 years, 18–85 µg/L for children aged 4–13 years, and 6–79 µg/L for adolescents aged 14–19 years. Earlier reported CgA reference intervals for adults have upper limits from 88 to 102 µg/L while no lower limits have been reported. The median for the three groups were 78, 51, and 39 µg/L, respectively. The median intra-individual variation was 14% (25%-centile 9.4%/75%-centile 21%).ConclusionsThe reference interval will be useful when screening, diagnosing, and monitoring children for NENs respecting the limitations plasma CgA has.

Vitamin B12 reference intervals on Beckman, Roche and Siemens analytical platforms

Tue, 09/12/2023 - 08:51
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundVitamin B12 status is assessed primarily by measuring total serum B12 using competitive binding methods. The lack of availability of a standard material and high-level reference measurement procedure affect the trueness of B12 results; this results in variation between methods. This study aimed to determine the reference intervals for vitamin B12 on three routine analytical platforms.MethodA prospective reference population of healthy individuals was recruited according to the IFCC CRIDL criteria. Vitamin B12 samples were measured on Roche, Beckman and Siemens analytical platforms.ResultsIn total, 300 adult subjects were recruited; the central 95th centile values for B12 for Roche (190–678 ng/mL) and Siemens (181–562 ng/mL) analytical platforms were in a close agreement. Beckman DXi, however, showed a significantly lower reference limit (110–562 ng/mL). All reference intervals are in keeping with previously published data but some are not in agreement with manufacturer provided reference interval.ConclusionAs the quality of the reference intervals plays a significant role in clinical outcome, it is of great importance that laboratories use a method-specific reference interval and if possible, locally derived reference intervals until further method standardization occurs.

Maintaining glucose integrity ex-vivo: Impact of preanalytical specimen handling

Thu, 09/07/2023 - 09:32
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundAdopting the WHO protocol for glucose analysis is arguably impractical in the routine clinical setting. Deviations may develop due to a lack of understanding regarding the impact of glycolysis on the accuracy of results.AimWe sought to assess the stability of glucose in two different blood collection tubes (BCT), BD Vacutainer® FX ‘Fl-Ox’ and Greiner Vacuette® FC-Mix ‘FC-Mix’ stored at room temperature (RT:18–22°C) and 4°C over 8.5 days.MethodEach participant provided venous whole blood collected into 51 BCTs; ‘Fl-Ox’ (n = 26) and ‘FC-Mix’ (n = 25). One Fl-Ox sample from each participant was handled according to the WHO recommended method. The remaining BCTs were stored at 4°C/RT prior to analyses at designated study timepoints. Glucose was measured using the hexokinase assay on the Cobas® 8000 platform.ResultsParticipants (n = 8, Male = 2) were aged 24–56 years. Plasma glucose measured in FI-Ox BCTs according to the WHO sample-handling method had a median concentration of 5.73 mmol/L (Range: 5.39–10.37 mmol/L). Glucose decreased by greater than minimal difference (>0.26 mmol/L) in blood collected into Fl-Ox and stored @4°C/RT within 24 h of phlebotomy. FC-Mix BCT maintained glucose <0.26 mmol/L @4°C over a period of 8.5 days and up to 4 days @RT when compared to the WHO recommended method.ConclusionGlucose in FC-Mix BCT stored @4°C demonstrated the best agreement with results determined using the WHO specifications. When FC-Mix tubes were stored @RT, glucose was stable for 4 days. These findings suggest that the FC-Mix BCT effectively inhibits glycolysis and should be introduced into routine clinical practice.

Practical approaches to the detection of macrotroponin

Sat, 09/02/2023 - 07:04
Annals of Clinical Biochemistry, Ahead of Print.
IntroductionMacrotroponin is increasingly recognised as a cause of confusion in interpreting high-sensitivity cardiac troponin (hs-cTnI) results. In this study, we sought to evaluate two practical approaches to detecting macrotroponin. These two approaches are PEG precipitation and SVM (support vector machine) analysis to classify discrepancies between hs-cTn assays.MethodResidual serum and heparin plasma specimens (n = 483) with initially elevated hs-cTnI from hospital and community laboratories were retested on multiple hs-cTn platforms before and after PEG precipitation and Protein A immunoglobulin depletion. SVM analysis was conducted to identify a linear equation that best discriminated specimens with macrotroponin using a combination of results from two different hs-cTn assays.FindingsThe diagnostic performance of PEG precipitation was carried out using Protein A immunoglobulin depletion as the reference comparator. When a cutoff residual activity after PEG precipitation of ≤ 20% was used, this threshold carried a high specificity of 92% (confidence interval 83–98%; n = 189) using the Siemens hs-cTnI Vista assay and 95% specificity (86%–98%; n = 242) using the Abbott hs-cTnI Architect assay. SVM analysis generated a linear equation identifying macrotroponin specimens from results obtained on two hs-cTn assays. This approach can be highly specific, comparable to PEG precipitation when certain assay combinations and concentrations are used.ConclusionWe describe and identify practical alternatives to detecting macrotroponin. These approaches can be optimised for high specificity, reducing the need for more complex laboratory methods.

Preliminary evaluation of the diagnostic performance of Roche Elecsys® active vitamin B12 versus total vitamin B12 for vitamin B12 deficiency screening

Thu, 08/31/2023 - 10:31
Annals of Clinical Biochemistry, Ahead of Print.
IntroductionThe prevalence of vitamin B12 deficiency is high in at-risk populations with sometimes irreversible consequences. Beside total B12 (TVB12), active B12 (AVB12) is a promising first-line marker. Only Abbott AVB12 assays were largely evaluated and generally demonstrated benefit in clinical practice. More recently developed Roche AVB12 still requires some investigations.ObjectivesOur study aimed to evaluate the Roche Elecsys® AVB12 immunoassay performance versus Roche Elecsys® TVB12 competition assay.Designand Methods: We included 175 patients at Rouen University Hospital who had a TVB12 value <300 pmol/L. We evaluated performance of AVB12 by comparing the results with TVB12 and MMA values in case of disagreement.ResultsPositive correlation was found between the AVB12 and TVB12. We found a disagreement between TVB12 and AVB12 in 18.8% of cases. Among 33 cases of disagreement, 76% had normal AVB12 but low TVB12, whereas 24% had low AVB12 and normal TVB12. Thirty-one MMA determinations were performed: 71% showed agreement between MMA and AVB12, versus 29% between MMA and TVB12. TVB12 reported a sensitivity (Se) at 66.7%, specificity (Sp) at 20%, positive predictive value (PPV) at 16.7% and negative predictive value (NPV) at 71.4% for the prediction of MMA elevation. We determined an optimized cut-off value of 45.5 pmol/L for AVB12, which reported a Se 66.7%, Sp 60%, PPV 30.7%, and NPV 88.9%.ConclusionsOur results provide preliminary evidence that Roche AVB12 may offer better discrimination than Roche TVB12 in the diagnosis of vitamin B12 deficiency. Further more detailed evaluation is warranted.

Current practice and recommendations for managing transgender patient data in clinical laboratories in the United Kingdom and Republic of Ireland

Thu, 08/31/2023 - 05:28
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundTransgender people may avoid seeking medical care due to previous negative experiences and fear of discrimination. Clinical laboratories can contribute to a poor patient experience and clinical outcome when the design and functionality of laboratory information management systems (LIMS) do not consider the needs of transgender patients. This survey aimed to capture current practices in United Kingdom and Republic of Ireland clinical laboratories concerning how transgender patient data and test requests are managed throughout the total testing process.MethodsAn anonymous survey was distributed to clinical laboratory professionals in November 2021. Thirty-three questions covered how gender variables are recorded for transgender patients and used to inform gender-specific calculations, test access, and reference intervals (RIs).ResultsOf the 66 respondents, 70% were based in laboratories in England, with a majority of laboratories having ISO 15189 accreditation and processing 1000–10,000 blood samples daily. Eighty-five percent stated that their LIMS had a single field recording sex or gender information. Forty-three percent did not limit test access based on gender, but 68% did not append RIs for patients with unknown or indeterminate gender.ConclusionsThis survey was the first to quantify how clinical laboratories manage sex and gender information and report results for transgender and non-binary patients, and details several key recommendations based on the survey responses.

Development of blood collection tubes for glucose measurement using adenosine 3-phosphate and sodium fluoride as glycolytic inhibitors

Thu, 08/31/2023 - 03:48
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundBlood collection tubes with sodium fluoride (NaF) added as a glycolytic inhibitor are widely used for glucose measurement. However, the glycolytic inhibitory effects of NaF are insufficient, and decreases in glucose levels over time after blood collection have become a problem.MethodsBlood from a volunteer collected using an NaF tube was used to compare the glycolysis inhibitory abilities of ATP and ADP. Blood samples from 10 volunteers were collected in NaF tubes and NaF tubes with added ATP (NaF–ATP tubes). The stability of glucose and haemoglobin (Hb)A1c after whole-blood storage from immediately after blood collection to 24 h later was compared.ResultsATP and ADP had similar inhibitory effects on glycolysis, but ATP was selected as an additive for blood collection tubes because ADP was more haemolytic than ATP. We verified the ability of NaF blood collection tubes supplemented with ATP to inhibit glycolysis. Mean (± standard deviation) glucose levels (n=10) after storage for 24 h after blood collection decreased to −9.0 ± 2.7 mg/dL (−0.50 ± 0.15 mmol/L) in conventional NaF tubes. NaF–ATP(20) tubes with 20 mg (0.036 mmol) ATP added showed a reduced decrease, with a mean of −5.8 ± 2.9 mg/dL (−0.32 ± 0.16 mmol/L). NaF–ATP tubes also had no effect on HbA1c measurement.ConclusionThis study reports on a blood collection tube that enables the measurement of glucose and HbA1c. Based on the results of validation, we conclude that NaF–ATP tubes can reduce decreases in glucose over time in stored whole blood compared to conventional NaF tubes.

UKMedLab2023 conference – A celebration of 70 years of the ACB

Wed, 08/30/2023 - 03:29
Annals of Clinical Biochemistry, Ahead of Print.

Use of finer needles for venipuncture increases in vitro haemolysis despite reducing persistent pain and nerve injury: A retrospective study

Tue, 08/29/2023 - 04:29
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundAlthough venipuncture is minimally invasive, and is the most frequently performed medical procedure, it carries the small risk of causing persistent pain, including nerve damage. Recently, our hospital stopped using 22-gauge needles for venipuncture in outpatients and switched to using only 23- and 25-gauge needles. We investigated the impact of using only the finer needles on the incidence of persistent or neuropathic pain and the prevalence of haemolysis, as well as the impact of haemolysis associated with the needle change on other laboratory data.MethodsWe retrospectively collected and analysed data on venipuncture-associated pain complaints made during the 1-year period prior and 1-year period after the change in needles, as well as the frequency of haemolysis before and after the change. We also focused on 90 cases that showed significant haemolysis after the needle change and compared the serum aspartate aminotransferase, lactate dehydrogenase, and potassium levels before and after the needle change.ResultsThe incidence of persistent pain was significantly reduced from 1 in 10,825 venipunctures before the change to 1 in 29,747 venipunctures after the change. Notably, no patients experienced neuropathic pain after the change. However, the prevalence of haemolysis was significantly increased. Additionally, the serum aspartate aminotransferase, lactate dehydrogenase, and potassium levels were significantly elevated in the cases that showed moderate to gross haemolysis after the needle change.ConclusionUsing finer needles involves both advantages and disadvantages, and careful consideration is needed to determine which type of needle is in the best interests of the patient.

Different serum sodium assay, different model for end stage liver disease - sodium scores in patients awaiting liver transplant: A cross-sectional study

Mon, 08/21/2023 - 04:08
Annals of Clinical Biochemistry, Ahead of Print.
Introduction and aimsSodium can be measured with direct or indirect methods; abnormal plasma total protein concentration can impact on sodium measured by indirect ion-selective electrodes (ISE). Serum sodium is an important item to determine the Model for End Stage Liver Disease Sodium (MELD-Na) score, commonly used for liver graft allocation. Patients with cirrhosis usually have hypoproteinemia. The aim of this study was to determine if there was a significant difference between the MELD-Na scores calculated based on the results of two different serum sodium ISE: indirect and direct.MethodsThis was a retrospective study; we included 166 patients that underwent liver transplant assessment, and that had paired (i.e. same date and time) direct and indirect sodium determinations. We calculated the MELD-Na scores with both sodium determinations, and we compared them.ResultsThere was a significant difference between MELD-Na scores; the mean difference was 0.4±1.3. If MELD-Na score had been determined by the sodium measured by the direct ISE, 69 patients (42%) would have stayed in the same place on the waiting list, 67 patients (40%) would have moved up, and 30 patients (18%) would have moved down.ConclusionsThere was a statistically significant difference between the MELD-Na scores calculated based on the two different sodium concentrations, which would theoretically result in changes in the order of the waiting list. This finding should prompt studies to assess if MELD-Na calculated based on direct methods has a better performance to predict clinically relevant outcomes.

Interference by paraproteins is an infrequent finding in nine Roche c702 assays

Fri, 08/11/2023 - 02:49
Annals of Clinical Biochemistry, Ahead of Print.

Analytical assays and bootstrap resampling method to validate performance of the Roche Elecsys STAT highly sensitive troponin T assay and its application for the ‘rule-out’ part of ESC guidelines for NTSTEMI

Mon, 08/07/2023 - 09:45
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundThe European Society of Cardiology (ESC) guidelines recommend a dynamic (0-1h) cardiac troponin (cTn) determination for non-ST elevation myocardial infarction diagnosis. For patients with low cTn levels, a discharge from emergency can be considered. Nevertheless, cTn cutoffs for discharge are lower than the limits of quantification proposed by laboratory reagent suppliers.AimValidate cTn assay on the Elecsys STAT kit.Materials and methodsPrecision, trueness, repeatability and within-laboratory variability were calculated from internal quality control and plasma pooled at 5.78 and 10.73 ng/L. Accuracy was calculated from external quality control. Uncertainty of measurement was calculated from (i) the uncertainty of the standard and control values and (ii) by precision from pooled plasma. Distribution of precision results from pooled plasma has been evaluated by bootstrap simulations. Dilution linearity tests with patient plasma were performed to evaluate the method for values near 5 ng/L.ResultsPrecision and trueness ranged from 1.35 to 4.45% and from 0.14 to −3.74%, respectively. Accuracy results ranged from 101.40 to 104.90%. Within laboratory variability was 2.91%. Uncertainty ranged from 3.66% to 19.90% for higher (2188) to lower values (5.78 ng/L). Bootstrap simulations allowed utilization of precision data from pooled plasma to evaluate cTn assay. The method was linear from 4.48 to 39.80 ng/L. A linear regression model best described the data.ConclusionElecsys STAT method provides accurate cTn results, including patients with cTn results categorizing them as ‘rule-out’ in the ESC guidelines.

Artefactually low creatinine by Beckman Coulter enzymatic method due to immunoglobulin M paraprotein interference

Mon, 07/24/2023 - 03:51
Annals of Clinical Biochemistry, Ahead of Print.
An 81-year-old man was admitted to hospital with symptomatic coronavirus disease (COVID-19) infection. He had a background of progressive chronic inflammatory demyelinating polyneuropathy associated with Waldenstrom’s macroglobulinaemia. His plasma creatinine on four separate samples was inconceivably low (all ≤13 μmol/L), as measured by a Beckman Coulter enzymatic assay) after being 72 μmol/L 3 months earlier. On further investigation, his serum immunoglobulin M (IgM) was 15.4 g/L and his plasma creatinine measured by Roche enzymatic and Roche Jaffe methods was 62 μmol/L and 64 μmol/L, respectively. This was consistent with results post dilution studies and polyethylene glycol (PEG) precipitation on the Beckman Coulter assay. There was no evidence of similar interference when reviewing creatinine results from 10 other patients with IgM paraproteinaemia who had been tested in our laboratory. Clinicians and laboratorians are reminded that enzymatic creatinine is not free from interferences. IgM paraprotein negative interference of enzymatic creatinine is rare and specific to a patient’s IgM and assay combination, but should be considered in patients with an unexplained low enzymatic creatinine result. Useful investigations to identify an interference include dilution studies, PEG precipitation and measuring creatinine on an alternative method such as Jaffe, mass spectrometry or an enzymatic method from a different platform.

A service evaluation of the use of faecal immunochemical tests in symptomatic patients aged under 50 years presenting to primary care

Mon, 07/17/2023 - 01:33
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundMost colorectal cancers (CRCs) occur in individuals aged over 50 years; however, the incidence in younger age groups is increasing. Diagnosis in younger patients is frequently delayed due to non-specific symptoms and the relative frequency of benign disease. There is a need to identify patients who warrant further investigation for CRC. This study reviewed whether a faecal haemoglobin (f-Hb) ≥10 μg Hb/g faeces measured by the faecal immunochemical test for f-Hb (FIT) was associated with CRC in a local primary care population aged under 50 years.Methodsf-Hb results from symptomatic patients aged 18–49 years presenting to primary care during a 17-month period were extracted from local laboratory information systems. Colonoscopy lists were obtained from three local trusts. The Somerset Cancer Registry was searched to identify CRCs. f-Hb and outcomes were matched using NHS numbers.ResultsA total of 3119 patients were included (median age 41 years); 313 of 2682 patients with f-Hb <10 μg/g (11.7%) and 305 of 437 patients with f-Hb ≥10 μg/g (69.8%) underwent colonoscopy. Twelve CRCs were detected. At a cut-off of 10 μg/g, the positivity rate was 14.0%, sensitivity was 100% (75.8–100%), specificity was 86.3% (85.1–87.5%), positive predictive value (PPV) was 2.7% (2.5–3.0%) and negative predictive value (NPV) was 100%. At a cut-off of 150 μg/g, sensitivity was 83.3% (55.2–95.3%), specificity was 95.2% (94.4–95.9%), PPV was 6.2% (4.7–8.2%) and NPV was 99.9% (99.8–100%).ConclusionOur data supports the use of FIT to triage patients aged under 50 years presenting to primary care with symptoms suggestive of CRCs.

Artificially raised creatinine concentrations due to analytical interference for samples contaminated with total parenteral nutrition fluid

Tue, 07/11/2023 - 08:36
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundA sample received in the laboratory from a patient receiving total parenteral nutrition (TPN) indicated that the patient may have renal dysfunction, but the results were not considered to be reliable enough to report. Investigations using a reference method for measurement of creatinine confirmed positive interference in the creatinine assay and distribution of samples via an External Quality Assessment (EQA) Scheme showed that this positive interference was method dependent.MethodsResidual TPN fluid (Nutriflex Lipid Special) left in the bag after the patient had completed the infusion was collected and added to a patient serum pool in increasing amounts and distributed to different laboratories for analysis of creatinine and glucose through an EQA Scheme.ResultsPositive interference in a number of different creatinine assays was identified as a result of a component in the TPN fluid. Positive interference from high concentrations of glucose has been demonstrated to be a cause for falsely high results in Jaffe creatinine assays.ConclusionsThe concern would be that a sample contaminated with TPN fluid would have both abnormal electrolytes and creatinine concentrations and give the impression that the patient was in renal failure due to analytical interference in the creatinine assay and laboratory staff need to be aware of this problem.

Variation of eGFR reporting and CKD equations used in the United Kingdom

Fri, 07/07/2023 - 09:36
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundUK Clinical laboratories have been routinely reporting an estimated glomerular filtration rate (eGFR) based on creatinine measurements using an eGFR equation since the early 2000s. Though there have been recommendations to use enzymatic based creatinine assays, and a recommendation of which equation to use, there still remains a high degree of variation in calculated eGFR results.MethodsData from the UK NEQAS for Acute and Chronic Kidney Disease Scheme have been reviewed to look at the CKD equations that are currently in use in the UK and the impact on eGFR results reported. The UK NEQAS for Acute and Chronic Kidney Disease has over 400 participants measuring creatinine across all major clinical biochemistry platforms.ResultsAn audit of EQA registration against results returned showed that in February 2022 at most 44% of registered participants were correctly reporting the 2009 CKD-EPI equation. At higher creatinine concentrations (which give rise to lower eGFR results), the spread of eGFRs is tight and there is little difference between results from different method principles. However, at lower creatinine concentrations, where it is known that there is more variation in creatinine depending on method choice, both method principle and eGFR equation choice can influence calculated eGFR. In some cases, this can impact CKD Stage classification.ConclusionsCKD is a serious public health issue that requires accurate assessment of eGFR. Laboratories should be in constant dialogue with their renal teams about their creatinine assay performance and impact on eGFR reporting across their service.

Standardising the biochemical confirmation of adult male hypogonadism; a joint position statement by the Society for Endocrinology and Association of Clinical Biochemistry and Laboratory Medicine*

Sat, 07/01/2023 - 06:03
Annals of Clinical Biochemistry, Ahead of Print.
Background: Inter-assay variation between different immunoassays and different mass spectrometry methods hampers the biochemical confirmation of male hypogonadism. Furthermore, some laboratories utilis eassay manufacturer reference ranges that do not necessarily mirror assay performance characteristics, with the lower limit of normality ranging from 4.9 nmol/L to 11 nmol/L. The quality of the normative data underlying commercial immunoassay reference ranges is uncertain.Design: A working group reviewed published evidence and agreed upon standardised reporting guidance to augment total testosterone reports. Results: Evidence-based guidance on appropriate blood sampling, clinical action limits, and other major factors likely to affect the interpretation of results are provided. Conclusions: This article aims to improve the quality of the interpretation of testosterone results by non-specialist clinicians. It also discusses approaches for assay harmonisation which have been successful in some but not all healthcare systems.

Serum cortisol assay performance following the 1 mg overnight dexamethasone suppression test

Fri, 06/30/2023 - 09:53
Annals of Clinical Biochemistry, Ahead of Print.
BackgroundThe 1 mg overnight dexamethasone suppression test (ONDST) is recommended for the differential diagnosis of Cushing’s syndrome and the investigation of adrenal incidentalomas. Despite documented variation in serum cortisol immunoassay performance, little has been published regarding its effect on the ONDST.AimsAssess the performance of three immunoassay platforms (Roche Elecsys II, Abbott Alinity & Siemens Centaur) when compared to a liquid chromatography tandem mass spectrometry (LC-MS/MS) method.MethodsSamples (n = 77) sent to the laboratory as part of an ONDST were retrieved prior to disposal, anonymized, and analysed on all platforms. Samples with factors impacting immunoassay analysis quality were excluded. Results were statistically compared to an LC-MS/MS method that previously demonstrated excellent comparability to a candidate reference method.ResultsThe Roche gen II showed a mean bias of −2.4 nmol/L and a Passing–Bablok fit of y = −0.9 + 0.97x. This was not affected by sex. The Abbott showed a mean bias −18.8 nmol/L, and a fit of y = −11.3 + 0.88x. This bias was −20.7 nmol/L in females versus −17.2 nmol/L in males. The Siemens had a mean bias of 2.3 nmol/L and a fit of y = 1.4 + 1.07x. This bias was 5.7 nmol/L in males versus −1.0 nmol/L in females.ConclusionsClinicians should be aware of the method-dependent variation that exists within serum cortisol analysis during the ONDSTs. Roche and Siemens aligned more closely with LC-MS/MS while the Abbot may cause a reduction in ONDST sensitivity. This data supports assay-specific cut-offs for the ONDST.