Evaluation of an ambulatory care pathway for patients with nitrous oxide-induced myeloneuropathy.

Introduction: Cases of nitrous oxide (N2O)-induced myeloneuropathy are increasing at UK hospitals. At our centre, a dedicated ambulatory care pathway, endorsed nationally, was established to treat and monitor patients with N2O-myeloneuropathy in 2021 and refined through three audit cycles. We analysed the outcomes of patients on this pathway to better understand factors associated with non-engagement. Alongside, a novel approach using WhatsApp for questionnaire delivery was trialled in an attempt to improve engagement with treatment. Methods: Patients on the N2O ambulatory care pathway were identified from MDT meeting lists from 9 September 2022 to 25 April 2023. Clinical data were collected via electronic clinical records, including the most recent neurological examination and reason for discharge from the pathway. Patients identified from MDT lists from 27 January 2023 to 14 March 2023 were approached to participate in weekly 12-item surveys, delivered via WhatsApp. This was approved as a service development project with approval for WhatsApp use given by the chief clinical information officer. Results: 35/56 (62.5%) patients were discharged from ambulatory care due to non-attendance and 17/56 (30.4%) completed their treatment course. The median time from initial presentation to discharge was 49 days. 24/40 (60.0%) of patients with a final neurological examination documented had a residual deficit, with objective sensory deficits most common. 12 patients were approached to receive weekly questionnaires via WhatsApp. 5/8 who expressed interest returned a consent form. All participants were withdrawn due to non-response or participant choice. 1/5 returned more than two surveys. Conclusion: Despite poor participation in surveys delivered via WhatsApp, novel approaches are needed to improve engagement with patients on the N2O ambulatory care pathway.

Fecal Calprotectin in Gastrointestinal Disease.

BACKGROUND: Inflammatory bowel disease (IBD) comprises a group of chronic conditions characterized by relapsing and remitting inflammation of the gastrointestinal tract. The incidence is increasing worldwide, and the therapeutic options for management are expanding. Endoscopy is the gold standard investigation for diagnosis of IBD and for assessing mucosal healing, which is increasingly being used as a measure of disease control. However, it is an invasive procedure that is unpleasant for patients and expensive and time-consuming for hospitals. Fecal calprotectin has been shown to be an accurate surrogate marker of gastrointestinal inflammation in IBD. CONTENT: Fecal calprotectin was initially used for the diagnosis of IBD but is now recognized as having a role in assisting in assessment of disease activity, prediction of relapse, and informing decisions around therapy and may help to minimize requirement for endoscopy. However, there are various preanalytical and analytical factors that can affect interpretation of the results; these need to be understood to optimize clinical care. SUMMARY: Preanalytical and analytical factors that can potentially influence fecal calprotectin concentrations are examined, and an overview is provided of clinical situations in which fecal calprotectin is commonly measured.

Faecal immunochemical testing (FIT) in primary care: a follow-up service evaluation.

AIM: Colorectal cancer (CRC) is the fourth most common cancer in the UK. Following National Institute for Health and Care Excellence guidance for faecal immunochemical testing (FIT), we introduced a service for the measurement of faecal haemoglobin (f-Hb) in symptomatic patients. Previously, we evaluated the first 6 months of the service in three local boroughs, here we re-examine the use of FIT, over a similar 6 months in the two successive years. METHODS: Patients who had FIT requested in April-September 2020 and 2021 were studied. Results were obtained from the laboratory information systems and matched with the clinical outcomes of those referred via the urgent lower gastrointestinal cancer pathway. Patient demographics, reason for referral, clinical outcome and diagnostic test performance are reported. RESULTS: In 2020, 4042 samples were analysed and 57 CRC detected. In 2021, 10 508 samples were analysed and 65 CRC detected. Six (4.9%) patients with CRC had f-Hb <10 µg/g, of whom three were anaemic. In 2020, 27.7% of samples were from patients under 50 years; and in 2021, 32.8%. Sensitivity, specificity, positive predictive value and negative predictive value of f-Hb at ≥10 µg/g for CRC were 92.9%, 46.6%, 6.4% and 99.4% in 2020 and 96.9%, 29.9%, 3.2% and 99.8% in 2021. CONCLUSIONS: As currently used in primary care in North East London, specificity of FIT at a cut-off of 10 µg/g is much lower than in published studies and the impact of this on colorectal services needs to be considered.

Faecal immunochemical testing for haemoglobin in detecting bowel polyps in symptomatic patients: multicentre prospective cohort study.

BACKGROUND: Measurement of faecal haemoglobin using faecal immunochemistry testing is recommended in patients presenting with symptoms suspicious for colorectal cancer, to aid in triage and prioritization of definitive investigations. While its role in colorectal cancer has been extensively investigated, the ability of faecal immunochemistry testing to detect adenomas in symptomatic patients is unclear. METHODS: A multicentre prospective observational study was conducted between April 2017 and March 2019, recruiting adults from 24 hospitals across England and 59 general practices in London who had been urgently referred with suspected colorectal cancer symptoms. Each patient provided a stool sample for faecal immunochemistry testing, in parallel with definitive investigation. A final diagnosis for each patient was recorded, including the presence, size, histology, and risk type of colonic polyps. The outcome of interest was the sensitivity of faecal immunochemistry testing in detecting the presence of adenomas. RESULTS: Of 3496 patients included in the analysis, 553 (15.8 per cent) had polyps diagnosed. Sensitivity of faecal immunochemistry testing for polyp detection was low across all ranges; with a cut-off for faecal haemoglobin of 4 µg/g or lower, sensitivity was 34.9 per cent and 46.8 per cent for all polyp types and high-risk polyps respectively. The area under the receiver operating characteristic curve in detection probability was relatively low for both intermediate-risk (0.63) and high-risk polyps (0.63). CONCLUSION: While faecal immunochemistry testing may be useful in prioritizing investigations to diagnose colorectal cancer, if used as a sole test, the majority of polyps would be missed and the opportunity to prevent progression to colorectal cancer may be lost.

Nitrous oxide-induced subacute combined degeneration of the cord: diagnosis and treatment.

Recreational use of nitrous oxide (N2O) has increased rapidly in recent years and is now the second most commonly used recreational drug among young people in the UK. There has been a corresponding rise in cases of nitrous oxide-induced subacute combined degeneration of the cord (N2O-SACD), a pattern of myeloneuropathy usually associated with severe vitamin B12 deficiency. This can cause serious and permanent disability in young people but, if recognised early, may be effectively treated. All neurologists should be aware of N2O-SACD and its treatment; however, there are currently no agreed guidelines. Based on our experience in East London, an area of high N2O use, we provide practical advice on its recognition, investigation and treatment.

Clinical evaluation of the OC-Sensor Pledia calprotectin assay.

OBJECTIVES: Faecal calprotectin (f-Cal) and faecal haemoglobin (f-Hb) are important tests for evaluation of gastrointestinal disease. Samples for measurement of f-Hb are taken by the patient directly into a specimen collection device containing stabilising buffer, which can be placed directly onto the analyser in the laboratory. Samples for f-Cal are usually sent in screw top pots and often require time-consuming extraction procedures prior to analysis. OC-FCa calprotectin is a new assay which uses the same specimen collection device and analyser as our current f-Hb assay. Analytical evaluation has already shown it to perform well but to have a positive bias. This study was a clinical evaluation to investigate the diagnostic test performance and cut-off suitable for its use in the diagnosis of IBD. METHODS: OC-FCa calprotectin was measured in a convenience sample of 603 patients in whom f-Hb had been requested and was found to be ≥10 µg/g. Clinical outcomes were obtained from notes, radiological reports and endoscopy and histology reports. RESULTS: A total of 425 patients completed clinical investigations; IBD was diagnosed in 49 and other colorectal pathology in 161. Median f-Cal in patients with IBD was 1,660 µg/g, significantly different (p<0.01) from those with other colorectal pathology (192 µg/g) or normal findings (157 µg/g). ROC curve analysis showed AUC of 0.898 with sensitivity of 91.8% and specificity of 79.3% at a cut-off of 600 µg/g. CONCLUSIONS: The new OC-FCa calprotectin assay performed well for the diagnosis of IBD using a cut-off of 600 µg/g.

Faecal calprotectin is not necessarily required as a screen for significant bowel disease in primary care.

OBJECTIVE: NICE recommends measurement of faecal haemoglobin (f-Hb) using faecal immunochemical test (FIT) when colorectal cancer is suspected and calprotectin (f-Cal) in the context of inflammatory bowel disease, though neither is disease specific. During the COVID-19 pandemic, f-Hb has been a requirement prior to referral for endoscopy in England; f-Cal is often performed simultaneously. The aim of this study was to investigate test performance of both tests for significant bowel disease in those patients referred. DESIGN: All adult patients with simultaneous measurements of f-Hb and f-Cal between April 2019 and September 2020 were included. For those referred, outcomes were determined from clinical records. RESULTS: 650 patients with simultaneous samples for f-Hb an f-Cal were managed in Primary Care; 319 patients were referred to hospital; SBD was found in 32 (10.0%) (CRC 5, high risk adenomas 5, IBD 22). At a cut-off of 10 µg/g for f-Hb and 200 µg/g for f-Cal, the sensitivity, specificity and negative predictive value for diagnosis of SBD were 84.4%, 58.2% and 96.7% and 68.8%, 89.6% and 95.7%, respectively. Performance of both tests would have enabled diagnosis of two more cases of significant, but non-malignant, bowel disease but required over 4% more referrals for investigation. CONCLUSION: Use of FIT has become established to assist prioritisation of patients for referral from Primary Care. Whilst introduced specifically for CRC, FIT performs well as a rule out for IBD in Primary Care and the use of f-Cal is not required.

Faecal immunochemical test for patients with 'high-risk' bowel symptoms: a large prospective cohort study and updated literature review.

BACKGROUND: We evaluated whether faecal immunochemical testing (FIT) can rule out colorectal cancer (CRC) among patients presenting with 'high-risk' symptoms requiring definitive investigation. METHODS: Three thousand five hundred and ninety-six symptomatic patients referred to the standard urgent CRC pathway were recruited in a multi-centre observational study. They completed FIT in addition to standard investigations. CRC miss rate (percentage of CRC cases with low quantitative faecal haemoglobin [f-Hb] measurement) and specificity (percentage of patients without cancer with low f-Hb) were calculated. We also provided an updated literature review. RESULTS: Ninety patients had CRC. At f-Hb < 10 µg/g, the miss rate was 16.7% (specificity 80.1%). At f-Hb < 4 µg/g, the miss rate was 12.2% (specificity 73%), which became 3.3% if low FIT plus the absence of anaemia and abdominal pain were considered (specificity 51%). Within meta-analyses of 9 UK studies, the pooled miss rate was 7.2% (specificity 74%) for f-Hb < 4 µg/g. DISCUSSION: FIT alone as a triage tool would miss an estimated 1 in 8 cases in our study (1 in 14 from meta-analysis), while many people without CRC could avoid investigations. FIT can focus secondary care diagnostic capacity on patients most at risk of CRC, but more work on safety netting is required before incorporating FIT triage into the urgent diagnostic pathway.

Use of ColonFlag score for prioritisation of endoscopy in colorectal cancer.

OBJECTIVE: Colorectal cancer (CRC) is the fourth most common cancer in UK. Symptomatic patients are referred via an urgent pathway and although most are investigated with colonoscopy <4% are diagnosed with cancer. There is therefore a need for a suitable triage tool to prioritise investigations. This study retrospectively examined performance of various triage tools in patients awaiting investigation on the urgent lower gastrointestinal cancer pathway DESIGN: All patients over 40 years of age on the urgent pathway awaiting investigation for suspected CRC on 1 May were included. After 6 months, outcomes were evaluated and the performance of the faecal immunochemical test (FIT), faecal haemoglobin concentration, age and sex test (FAST) and the artificial intelligence algorithm ColonFlag were examined. RESULTS: 532 completed investigations and received a diagnosis; 15 had CRC. 388 had a valid FIT result, of whom 11 had CRC; FAST Score ≥4.5 had sensitivity of 72.7%, specificity of 80.6% and would have failed to detect three tumours. Faecal haemoglobin (f-Hb) at cut-off of 10 µg/g and ColonFlag had equal sensitivity of 81.82%, ColonFlag had greater specificity 73.47%, compared with 64.99%. Both tests would have failed to detect two tumours but not in the same patients; when used in combination, sensitivity and specificity were 100% and 49.4%. When ColonFlag was applied to the cohort of 532, an additional four tumours would have been detected in patients without a valid FIT. CONCLUSION: This study showed ColonFlag to have equal sensitivity and greater specificity than f-Hb at a cut-off of 10 µg/g as a triage tool for CRC.

Use of faecal immunochemical testing as an alternative to faecal calprotectin in children.

BACKGROUND: Faecal calprotectin has been widely used as a non-invasive marker of intestinal inflammation in children. Measurement of faecal haemoglobin using faecal immunochemical test is well established in adults for detection of colorectal cancer. In adults, faecal haemoglobin has been recommended as a reliable tool to aid identification of those at low risk of significant bowel disease and has also been used in inflammatory bowel disease to assess mucosal healing. AIMS: We aimed to evaluate the performance of faecal haemoglobin in the paediatric population and compare it with faecal calprotectin. METHODS: Children being assessed in the paediatric gastroenterology clinic for bowel symptoms had a sample sent for both faecal calprotectin and faecal haemoglobin. Samples were collected over a 10-month period from November 2018 to September 2019. Faecal haemoglobin was measured using an OC-Sensor. Faecal calprotectin was measured using Liason®Calprotectin. RESULTS: One hundred forty three samples were returned for faecal haemoglobin and in 107 a paired faecal calprotectin was also available. Faecal haemoglobin correlated with faecal calprotectin, Spearman's rank coefficient 0.656 (P < 0.0001). There were 35 patients with faecal haemoglobin >20 µg/g and in 32 of these patients faecal calprotectin was >200 µg/g; 74 patients with faecal haemoglobin and 38 patients with faecal calprotectin underwent colonoscopy. Patients with normal histology had faecal haemoglobin <4 µg/g; faecal haemoglobin >20 µg/g was associated with signification inflammation. CONCLUSION: Our study is the first to compare faecal haemoglobin and faecal calprotectin in a paediatric population. Results suggest that faecal haemoglobin correlates with faecal calprotectin and, as in adults, may be useful to rule out significant bowel disease. A faecal haemoglobin >20 µg/g was consistent with significant histological inflammation.

Service evaluation of faecal immunochemical testing introduced for use in North East London for patients at low risk of colorectal cancer.

AIMS: Colorectal cancer (CRC) is the fourth most common cancer in the UK. Following National Institute of Clinical Excellence (NICE) guidance for faecal immunochemical testing (FIT) (DG30), we introduced a service for the measurement of faecal haemoglobin (fHb) in symptomatic patients in line with the 2017 update of the NG12 guidance. The purpose of this study was to audit the use of FIT, focussing on the indication for request and referral for diagnostic tests as recommended in NICE guidance. METHODS: Testing was rolled out after careful introduction with extensive education led by the local Cancer Alliance and reinforced by the laboratory. After 6 months, the outcomes of all patients tested were reviewed. RESULTS: 1203 samples were received, of which 894 (74.3%) were suitable for analysis. Of these, 482 (53.9%) actually met the criteria for FIT analysis stipulated in our patient pathway. Eight patients were diagnosed with CRC; fHb was detectable in all and was ≥200 µg/g in seven and <10 µg/g in one. 217 patients underwent gastrointestinal investigations, and the sensitivity and specificity of FIT for CRC were found to be 87.5% (95% CI 46.6% to 99.7%) and 52.6% (95% CI 45.6% to 59.6%), respectively. Patients with anaemia were more likely to have fHb ≥10 µg/g. CONCLUSIONS: These findings suggest benefits from the introduction of FIT in terms of more efficient use of diagnostic investigations, while revealing initial problems relating to familiarity with a new test. This merits further intervention with education and awareness programmes for Primary Care and further audit.

Relationship between faecal metronidazole and lactoferrin concentrations to clinical response of patients with Clostridioides difficile.

OBJECTIVES: We investigated patients with Clostridioides difficile-associated diarrhoea to see if clinical resolution correlated with faecal concentrations of metronidazole or markers of inflammation. METHODS: Faecal metronidazole, lactoferrin and serum CRP were measured daily. These were then compared with clinical progress. RESULTS: Metronidazole concentration correlated with lactoferrin (ρ = 0.17, p = 0.015), CRP (ρ = 0.23, p < 0.001) and number of diarrhoeal stools per day (ρ = 0.29, p < 0.001). Lactoferrin correlated with CRP (ρ = 0.57, p < 0.001) and the number of diarrhoeal stools per day (ρ = 0.52, p < 0.001) as did CRP (ρ = 0.52, p < 0.001). CONCLUSIONS: We found no association between cessation of diarrhoea and metronidazole or lactoferrin concentrations. There was a relationship between metronidazole concentrations and markers of inflammation and stool frequency.

Potential roles of artificial intelligence learning and faecal immunochemical testing for prioritisation of colonoscopy in anaemia.

Iron deficiency anaemia (IDA) is the most common cause of anaemia and a frequent indication for colonoscopy, although the prevalence of colorectal cancer (CRC) in IDA is low. Measurement of faecal haemoglobin by immunochemical techniques (FIT) is used to detect symptomatic patients. We studied FIT in patients with anaemia attending a gastroenterology clinic in Plymouth and looked at an artificial intelligence (AI) learning algorithm (ColonFlag™) in these patients, together with a cohort who had undergone colonoscopy for IDA in London. Of 592 patients referred on the basis of haemoglobin concentration, 21 (3.5%) had CRC. Using ColonFlag™, rather than haemoglobin concentration, in combination with symptoms, would have resulted in prioritisation of 304 patients for urgent referral rather than 592. One CRC would have been missed but might have been detected by FIT, which was not available in this case. In patients aged <55 years in whom the incidence of CRC is low, 15 rather than 109 patients would have been prioritised for urgent referral with no cancers missed. FIT has a high negative predictive value in IDA so its use may enable some patients to avoid investigation and AI learning may be a more useful trigger than haemoglobin concentration for urgent referral for colonoscopy.

Fecal Calprotectin.

Calprotectin is a 36kDa member of the S100 family of proteins. It is derived predominantly from neutrophils and has direct antimicrobial effects and a role within the innate immune response. Calprotectin is found in various body fluids in proportion to the degree of any existing inflammation and its concentration in feces is about six times that of plasma. Measurement of fecal calprotectin is a useful surrogate marker of gastrointestinal inflammation. It has a high negative predictive value in ruling out inflammatory bowel disease (IBD) in undiagnosed, symptomatic patients and a high sensitivity for diagnosing the disease making it useful as a tool for prioritising endoscopy. In patients with known IBD, fecal calprotectin can be a useful tool to assist management, providing evidence of relapse or mucosal healing to enable therapy to be intensified or reduced. There are a number of commercial calprotectin assays with marked difference in performance as judged by external quality assessment and at present no standardised reference material exists. Various factors may affect results including age, medication and day to day variation. Laboratories should therefore be mindful of the characteristics of their own assay and factors that may affect results.

Multiple myeloma and acquired von Willebrand disease: a combined cause of preanalytical interference causing gel formation?

We report a patient with acquired von Willebrand disease, associated with multiple myeloma. At one stage in his illness, we were unable to analyse a sample sent in a serum separator tube, due to the presence of a gel within the separated serum layer. We suggest this was due to anomalous position of the gel because of the density of the sample caused by its high total protein concentration, exacerbated by fibrin strand formation because of inhibition of appropriate fibrin clot formation secondary to clotting disorder.

Development and validation of a liquid chromatography tandem mass spectrometry assay for the measurement of faecal metronidazole.

BACKGROUND: Metronidazole is an oral antibiotic which is widely used in the treatment of patients with Clostridium difficile associated disease. METHODS: This article describes the validation of a LC-MS/MS assay for the measurement of metronidazole in human faecal samples. RESULTS: Matrix matched and aqueous standards showed no significant difference in performance for the routine calibration of the assay. D4 deuterated metronidazole internal standard eluted with a different retention time to the undeuterated metronidazole on chromatography, hence zidovudine was used as an internal standard. Ion suppression was noted for both metronidazole and zidovudine due to unidentified compounds present in the faecal matrix and this was improved by extracting a smaller quantity of faeces and diluting the extract prior to analysis. Measurement uncertainty was 13% at 28,400ng/ml, 7.2% at 3300ng/ml, 3.9% at 320ng/ml, 13.6% at 109ng/ml and 30.9% at 20ng/ml. The assay was shown to be linear on dilution and the sensitivity of the assay was superior to HPLC assays using UV detection. The limit of detection was 5ng/ml, the limit of quantitation was 66ng/ml and the upper limit of the working range was 30,000ng/ml. Patient samples were stable at -20°C for 12months and extracted faecal samples were stable on storage for 1week at 4°C. There were no specific requirements for patient preparation or time of sample collection relative to taking metronidazole. CONCLUSIONS: Metronidazole can be quantified in faecal samples using LC-MS/MS which opens up opportunities for further research in this area.

Factors affecting blood sample haemolysis: a cross-sectional study.

OBJECTIVE: To determine the effect of blood sampling through an intravenous catheter compared with a needle in Emergency Department blood sampling. METHODS: We undertook a prospective, cross-sectional study in a UK university teaching hospital Emergency Department. A convenience sample of 985 patients who required blood sampling via venepuncture was collected. A total of 844 complete sets of data were analysed. The median age was 63 years, and 57% of patients were male. The primary outcome measure was the incidence of haemolysis in blood samples obtained via a needle compared with samples obtained via an intravenous catheter. Secondary outcome measures defined the effect on sample haemolysis of the side of the patient the sample was obtained from, the anatomical location of sampling, the perceived difficulty in obtaining the sample, the order of sample tubes collected, estimated tourniquet time and bench time. Data were analysed with logistic regression, and expressed as odds ratios (95% confidence intervals; P-values). RESULTS: Blood samples obtained through an intravenous catheter were more likely to be haemolysed than those obtained via a needle, odds ratio 5.63 (95% confidence interval 2.49-12.73; P<0.001). CONCLUSION: Blood sampling via an intravenous catheter was significantly associated with an increase in the likelihood of sample haemolysis compared with sampling with a needle. Wherever practicable, blood samples should be obtained via a needle in preference to an intravenous catheter. Future research should include both an economic evaluation, and staff and patient satisfaction of separating blood sampling and intravenous catheter placement.

Faecal calprotectin as a marker for oesophago-gastric cancer.

BACKGROUND: Faecal calprotectin has been shown to be useful as a non-invasive screening test to differentiate functional from organic bowel disease, and it has been noted to be elevated in colorectal cancer. The aim of this study was to describe concentrations of faecal calprotectin in patients with oesophago-gastric cancer and investigate any potential discriminatory power of the test. PATIENTS: Faecal calprotectin was measured in samples from 39 patients with known oesophago-gastric cancer and in 191 samples from control subjects. RESULTS: The median calprotectin concentration was < 20 µg/g (range < 20-421 µg/g) in control subjects and 97 µg/g (range < 20-940 µg/g) in patients with oesophago-gastric cancer (P < 0.001). A receiver operating characteristic curve gave an area under the ROC curve of 0.84 and a sensitivity of 76.9% (95% CI: 63.7-90.1%) and specificity of 88.0% (95% CI: 83.3-92.6%) at a cutoff of 50 µg/g. CONCLUSION: Faecal calprotectin is elevated in patients with cancer of the upper gastrointestinal tract. This study suggests that calprotectin may be promising in discriminating cancer patients from controls, but further work is required to explore any potential role of faecal calprotectin in screening for, or diagnosis of, oesophago-gastric cancer.

Appropriateness of prescribing thyroxine in primary care.

INTRODUCTION: A practice hypothyroid register is part of the quality and outcomes framework. In literature, the prevalence of hypothyroidism is stated to be 2% but the prevalence, defined from quality and outcomes framework data, is 3.2% in the UK and 3.6% in Plymouth. We sought to investigate the diagnosis of hypothyroidism and reasons for prescription of thyroxine to patients on the hypothyroid register in Plymouth. METHODS: A letter was sent to the 10 practices with the highest prevalence of hypothyroidism requesting a list of patients on their registers. The hospital pathology system was used to identify those with biochemically documented hypothyroidism (defined as thyroid stimulating hormone >10 mU/L) For two large practices the clinical records of the remaining patients were reviewed to ascertain the reasons for prescription of thyroxine and whether it led to symptomatic improvement. RESULTS: Seven practices responded with 1246 patients on their registers, of whom 43.6% had documented hypothyroidism. A review of notes of patients on the register, but without documented hypothyroidism, showed <25% to have an improvement in symptoms after prescription of thyroxine. Tiredness was the most common symptom prompting prescription of thyroxine. CONCLUSION: Of the patients on the register, only 43.6% had documented biochemical evidence of hypothyroidism and, from notes review of those without documented hypothyroidism, at least two-thirds may have been prescribed thyroxine outwith current national guidance. If this is correct, it has significant resource implications, impacts upon the workload of primary care, pharmacy and the laboratory service and may have clinical implications for patients.

An immunoglobulin G complexed form of thyroid-stimulating hormone (macro thyroid-stimulating hormone) is a cause of elevated serum thyroid-stimulating hormone concentration.

BACKGROUND: Macrocomplexes can be the cause of elevated serum hormone concentrations and may cause diagnostic confusion. This is well recognized for prolactin and commonly screened for using polyethylene glycol (PEG) precipitation. The phenomenon and a suitable screening method is less familiar with respect to thyroid-stimulating hormone (TSH). METHOD: Samples sent to the laboratory for routine analysis of thyroid function and found to have a TSH >10 mU/L were evaluated to determine the prevalence of macro-TSH in the Roche Elecsys assay, using PEG precipitation with confirmation by gel filtration chromatography. RESULTS: Of 495 samples tested, 3 (0.6%) were found to have macro-TSH. From the distribution of recoveries, a cut-off <25% was determined for identifying samples requiring further investigation for the presence of macro-TSH. CONCLUSION: The prevalence of elevated TSH due to macro-TSH was found to be 0.6%. Laboratories should be aware of this cause of assay interference.