Early Metabolic Disruption and Predictive Biomarkers of Delayed-Cerebral Ischemia in Aneurysmal Subarachnoid Hemorrhage.

Delayed cerebral ischemia (DCI) following aneurysmal subarachnoid hemorrhage (aSAH) is a major cause of complications and death. Here, we set out to identify high-performance predictive biomarkers of DCI and its underlying metabolic disruptions using metabolomics and lipidomics approaches. This single-center prospective observational study enrolled 61 consecutive patients with severe aSAH; among them, 22 experienced a DCI. Nine patients without aSAH were included as validation controls. Blood and cerebrospinal fluid (CSF) were sampled within the first 24 h after admission. We identified a panel of 20 metabolites that, together, showed high predictive performance for DCI. This panel of metabolites included lactate, cotinine, salicylate, 6 phosphatidylcholines, and 4 sphingomyelins. The interplay of the metabolome and the lipidome found between CSF and plasma in our patients underscores that aSAH and its associated DCI complications can extend beyond cerebral implications, with a peripheral dimension as well. As an illustration, early biological disruptions that might explain the subsequent DCI found systemic hypoxia driven mainly by higher blood lactate, arginine, and proline metabolism likely associated with vascular NO and disrupted ceramide/sphingolipid metabolism. We conclude that targeting early peripheral hypoxia preceding DCI could provide an interesting strategy for the prevention of vascular dysfunction.

Human Pancreatic Islets React to Glucolipotoxicity by Secreting Pyruvate and Citrate.

Progressive decline in pancreatic beta-cell function is central to the pathogenesis of type 2 diabetes (T2D). Here, we explore the relationship between the beta cell and its nutritional environment, asking how an excess of energy substrate leads to altered energy production and subsequent insulin secretion. Alterations in intracellular metabolic homeostasis are key markers of islets with T2D, but changes in cellular metabolite exchanges with their environment remain unknown. We answered this question using nuclear magnetic resonance-based quantitative metabolomics and evaluated the consumption or secretion of 31 extracellular metabolites from healthy and T2D human islets. Islets were also cultured under high levels of glucose and/or palmitate to induce gluco-, lipo-, and glucolipotoxicity. Biochemical analyses revealed drastic alterations in the pyruvate and citrate pathways, which appear to be associated with mitochondrial oxoglutarate dehydrogenase (OGDH) downregulation. We repeated these manipulations on the rat insulinoma-derived beta-pancreatic cell line (INS-1E). Our results highlight an OGDH downregulation with a clear effect on the pyruvate and citrate pathways. However, citrate is directed to lipogenesis in the INS-1E cells instead of being secreted as in human islets. Our results demonstrate the ability of metabolomic approaches performed on culture media to easily discriminate T2D from healthy and functional islets.

Congenital Hypothyroidism due to a Low Level of Maternal Thyrotropin Receptor-Blocking Antibodies.

INTRODUCTION: Maternal TSH receptor antibodies (TRAbs) can cross the placenta and affect fetal and neonatal thyroid function. Maternal TSH receptor-blocking antibodies (TBAbs) are a rare cause of congenital hypothyroidism. CASE REPORT: Following the discovery of a highly elevated TSH on her neonatal screening test, a 10-day-old girl with no familial history of thyroid disorder was referred to the pediatric endocrinology unit. Hypothyroidism was confirmed with a highly elevated TSH (817 mIU/L, reference range 0.4-3.1) and very low levels of FT4 (1.8 pmol/L, reference range 12-22). Anti-TPO antibodies were at 81 IU/mL (reference range <34), TRAbs at 1.7 IU/L (reference range <1.75), and thyroglobulin at 9.4 µg/L (reference range 3.5-77). The thyroid appeared normal on ultrasonography, and no radioiodine uptake was seen on the scintigraphy after the perchlorate discharge test. Concomitantly, a severe maternal hypothyroidism was discovered (TSH 224 mIU/L). The maternal ultrasound appeared normal, anti-TPO antibodies were moderately elevated, and TRAbs were at 3.2 IU/L. TBAbs activity was measured in the mother and her daughter, and a very high and similar blocking activity was observed in both patients (TBAbs 89%, reference range <10%). L-thyroxine treatment was introduced in the newborn and was successfully discontinued at 6.5 months of age, as the TBAbs activity decreased. CONCLUSION: We report herein a case of transient congenital hypothyroidism with a normal neonatal TRAbs level. In case of maternal TBAbs, similar activity of maternal TBAbs must be expected in the neonate, independently of the neonatal level of TRAbs.

Graves' Disease during Immune Checkpoint Inhibitor Therapy (A Case Series and Literature Review).

Thyrotoxicosis is an adverse event associated with immune checkpoint inhibitors (ICPis) that occurs in 0.6 to 3.2% of treated patients, depending on ICPi class. Presentation usually consists of a biphasic thyroiditis with transient thyrotoxicosis and secondary hypothyroidism. ICPi-induced Graves' disease (GD), due to the stimulating activity of TSH-receptor autoantibodies (TRAb), is extremely rare. The aim of this retrospective study was to describe the characteristics and evolution of GD during ICPi therapy. Five among 243 patients followed for ICPi-induced thyrotoxicosis showed TRAb positivity (2% of the cohort). GD occurred quickly after initiation of ICPis; its course was typical for two patients, with prolonged requirement for antithyroid drug treatment (ATD). The three other patients experienced biphasic thyroiditis with secondary hypothyroidism requiring long-term substitution. Three other patients had a diagnosis of GD before starting ICPis; they evolved toward hypothyroidism with early cessation of ATD and long-term substitution treatment during ICPi treatment. None developed significant Graves' orbitopathy. ICPi treatment was not interrupted for thyroid dysfunction. In conclusion, GD is a rare, immune-related adverse event of ICPis with an unusual course and frequent evolution to biphasic thyroiditis. In the case of ICPi-induced thyrotoxicosis in the presence of TRAb, observing the spontaneous evolution and performing a scintigraphy are useful before starting ATD treatment. Pre-existing GD is not exacerbated by ICPis and tends to evolve towards hypothyroidism. ICPi treatment can be maintained with adequate biochemical surveillance.

Analytical validation of eight methods of thyroglobulin measurement in fine-needle aspiration washouts.

BACKGROUND: Thyroglobulin (Tg) assay in washout fluids of fine needles, after cervical lymph nodes aspiration, is used for detecting metastases from differentiated thyroid carcinomas. Assay methods are the same as for Tg in serum. However, with non-serum samples, methods require extensive validation to notably check for the absence of matrix effect. This study fits this context. Our objectives were to assess analytic performances, in washout fluid, of eight different Tg assay methods and to compare them to validated data in serum. METHODS: Eleven medical laboratories participated in this study. The matrix tested was phosphate-buffer saline containing 1% bovine serum albumin (PBS-1% BSA). Samples used were dilutions, in this buffer, of Certified Reference Material (CRM 457). We verified, for all methods, the limit of detection, precision, linearity, trueness and accuracy. RESULTS: In PBS-1% BSA, the functional sensitivities (FS) were comparable to those expected for serum. All the methods were linear. The relative biases of trueness were between -24.5 and 10.2% around 1 µg/L. Total analytical error was ≤40% near the functional sensitivity values. CONCLUSION: No quantitatively important matrix effect was observed. All the methods showed their ability to measure Tg in PBS-1% BSA, over the concentration range of interest, with acceptable total analytical error. We validated the functional sensitivity value as a decision threshold in thyroidectomized patients after treatment and with low concentrations of serum Tg.

Subclinical Hypothyroidism: is it Really Subclinical with Aging?

No recent study has focused on clinical features of subclinical hypothyroidism (SCH), especially in older patients. TSH measurement has remarkably evolved these last 20 years and thus reconsideration is needed. In our prospective multicenter study (2012-2014) including 807 subjects aged <60 years (<60y) and 531 subjects ≥60 years (≥60y), we have monitored 11 hypothyroidism-related clinical signs (hCS) together with TSH, FT4, FT3 and anti-thyroperoxidase antibodies values. hCS expression has been compared in patients with SCH vs euthyroidism in each age group. The number of hCS above 60y of age were found to be more elevated in the euthyroid population (1.9 vs 1.6, p<0.01) than in the SCH population (2.3 vs 2.6, p=0.41) while increase in hCS is limited to SCH subjects in the <60y group (p<0.01). The percentage of subjects with at least 3 signs increased with SCH in the <60y group (42.6% vs 25.0%, p<0.01) but not ≥60y (34.4% vs 33.9%, p=0.96). In older individuals, only three hCS could be related to both SCH and a decreased T3/T4-ratio (0.26 vs 0.27, p<0.01), suggesting either a reduced activity of TSH, or an adaptive response with aging. While hCS are clearly associated with SCH in patients <60y, they are not so informative in older subjects. TSH measurements carried out on the basis of hCS need to be interpreted with caution in aged patients. A reassessment of the TSH reference range in older patients is clearly needed and should be associated to more appropriate monitoring of thyroid dysfunction.

Differential Effect of Glucose on ER-Mitochondria Ca2+ Exchange Participates in Insulin Secretion and Glucotoxicity-Mediated Dysfunction of ß-Cells.

Glucotoxicity-induced ß-cell dysfunction in type 2 diabetes is associated with alterations of mitochondria and the endoplasmic reticulum (ER). Both organelles interact at contact sites, defined as mitochondria-associated membranes (MAMs), which were recently implicated in the regulation of glucose homeostasis. The role of MAMs in ß-cells is still largely unknown, and their implication in glucotoxicity-associated ß-cell dysfunction remains to be defined. Here, we report that acute glucose treatment stimulated ER-mitochondria interactions and calcium (Ca2+) exchange in INS-1E cells, whereas disruption of MAMs altered glucose-stimulated insulin secretion (GSIS). Conversely, chronic incubations with high glucose of either INS-1E cells or human pancreatic islets altered GSIS and concomitantly reduced ER Ca2+ store, increased basal mitochondrial Ca2+, and reduced ATP-stimulated ER-mitochondria Ca2+ exchanges, despite an increase of organelle interactions. Furthermore, glucotoxicity-induced perturbations of Ca2+ signaling are associated with ER stress, altered mitochondrial respiration, and mitochondria fragmentation, and these organelle stresses may participate in increased organelle tethering as a protective mechanism. Last, sustained induction of ER-mitochondria interactions using a linker reduced organelle Ca2+ exchange, induced mitochondrial fission, and altered GSIS. Therefore, dynamic organelle coupling participates in GSIS in ß-cells, and over time, disruption of organelle Ca2+ exchange might be a novel mechanism contributing to glucotoxicity-induced ß-cell dysfunction.

Three Consecutive Pregnancies in a Patient with Chronic Autoimmune Thyroid Disease Associated with Hypothyroidism and Extremely High Levels of Anti-Thyrotropin Receptor Antibodies.

Background: Thyroid-stimulating hormone (TSH) receptor (TSHR) antibodies (TRAb) can be present in chronic autoimmune thyroiditis. Transplacental TRAb transfer can lead to fetal thyroid dysfunction and serious complications. Patient Findings: We report the case of a woman with autoimmune hypothyroidism and extremely high TRAb levels, with blocking and stimulating activities (biological activities characterized with Chinese hamster ovary cells expressing TSHR). At week 22 of her first pregnancy, sonography detected fetal growth retardation and cardiac abnormalities (extreme tachycardia, right ventricular dilatation, pericardial effusion). The mother's TRAb level, assayed later, was 4030 IU/L (n < 10). Delivered via caesarean section gestational week 30, the newborn girl had several malformations, signs of malnutrition, goiter and hyperthyroidism associated with elevated TRAb (1200 IU/L). The newborn died 26 days after delivery. Faced with persistently high TRAb levels and a desire to become pregnant again, the woman was treated with three consecutive 740-MBq activities of iodine-131, which resulted in a decrease in TRAb to 640 IU/L. The patient had two subsequent pregnancies 16 and 72 months after the radioiodine administration. During the close follow-ups, fetal development was normal, and initial TRAb levels during the two pregnancies were 680 and 260 IU/L, respectively, which initially decreased but then increased in late pregnancy. In both cases, labor was induced at 34 weeks. The newborns, mildly hyperthyroid at birth, required carbimazole treatment at days 5 and 2, respectively. The mild hyperthyroidism despite high TRAb levels was likely due to the concomitant presence of stimulating and blocking TRAb. The two girls, now aged 12 and 8 years, are in good health. The mother has no detectable thyroid gland tissue and is euthyroid on levothyroxine (175 µg/d). Her TRAb level gradually decreased to 136 IU/L. Summary and Conclusions: This remarkable case illustrates the severe consequences of untreated fetal hyperthyroidism and the need to assay and follow-up TRAb levels in women of reproductive age with autoimmune thyroiditis.

Inappropriate glucagon and GLP-1 secretion in individuals with long-standing type 1 diabetes: effects of residual C-peptide.

AIMS/HYPOTHESIS: Recent studies have demonstrated that residual beta cells may be present in some people with long-standing type 1 diabetes, but little is known about the potential impact of this finding on alpha cell function and incretin levels. This study aimed to evaluate whether insulin microsecretion could modulate glucagon and glucagon-like peptide-1 (GLP-1) responses to a mixed meal tolerance test (MMTT). METHODS: Adults with type 1 diabetes onset after the age of 15 years (n = 29) underwent a liquid MMTT after an overnight fast. Insulin microsecretion was defined when peak C-peptide levels were >30 pmol/l using an ultrasensitive assay. Four individuals with recent-onset type 1 diabetes were included as controls. Glucagon and GLP-1 responses were analysed according to C-peptide patterns. RESULTS: We found comparable peak values, Δ0-max levels and AUCs of glucagon and GLP-1 responses in C-peptide-positive participants (n = 9) and C-peptide-negative participants (n = 16) with long-standing diabetes and in participants with recent-onset diabetes (n = 4). Mean glucagon levels, however, differed (p = 0.01). Mean GLP-1 responses were significantly lower according to C-peptide positivity (p < 0.001, ANOVA). Interestingly, GLP-1 levels correlated to glucagon values in C-peptide-positive participants with long-standing diabetes (Pearson's r = 0.915, p = 0.004) and in participants with recent-onset diabetes (p < 0.001) but not in C-peptide-negative participants. CONCLUSIONS/INTERPRETATION: The glucagon response to an MMTT in people with long-standing type 1 diabetes is not reduced by the presence of residual beta cells. The reduction of GLP-1 responses according to residual C-peptide levels suggests specific regulatory pathways.

Diabetes mellitus induced by PD-1 and PD-L1 inhibitors: description of pancreatic endocrine and exocrine phenotype.

AIMS: Programmed cell death-1 and programmed death ligand 1 (PD-1/PD-L1) inhibitors restore antitumor immunity, but many autoimmune side-effects have been described. Diabetes mellitus is a rare complication, and little data concerning its pathophysiology and phenotype have been published. This study aimed to describe both pancreatic endocrine and exocrine functions, immunological features and change in pancreas volume in subjects with diabetes mellitus induced by PD-1 and PD-L1 inhibitors. METHODS: We analyzed the data of six subjects treated with immunotherapy who presented acute diabetes. RESULTS: There were five men and one woman. Median age was 67 years (range 55-83). Three subjects were treated with nivolumab, two with pembrolizumab and one with durvalumab. Median time to diabetes onset after immunotherapy initiation was 4 months (range 2-13). Four patients presented fulminant diabetes (FD); none of these had type 1 diabetes (T1D)-related autoantibodies, none of them had T1D or FD-very high-risk HLA class II profiles. The bi-hormonal endocrine and exocrine pancreatic failure previously reported for one FD patient was not found in other FD subjects, but glucagon response was blunted in another FD patient. Pancreas volume was decreased at diabetes onset in 2 FD patients, and all patients presented a subsequent decrease of pancreas volume during follow-up. CONCLUSIONS: In the patients presented herein, immunotherapy-induced diabetes was not associated with T1D-related autoantibodies. The hormonal and morphological analysis of the pancreatic glands of these six cases contributes to the understanding of the underlying and probably heterogeneous mechanisms. There is a need to find biomarkers to identify patients at risk to develop these new forms of diabetes at early stages of the process to prevent ketoacidosis and to evaluate preventive strategies.

Variability among TSH Measurements Can Be Reduced by Combining a Glycoengineered Calibrator to Epitope-Defined Immunoassays.

OBJECTIVES: Measuring protein markers with variable glycosylation, such as thyroid-stimulating hormone (TSH), with high accuracy is not an easy task. Despite highly sensitive third-generation tests, discrepancies among TSH assays still remain unsolved and are the focus of important standardization efforts. Earlier work from our group showed that a lack of similarity in epitope expression between standards and samples may account for discordant hormone measurements. In this study, we aimed at producing a glycoengineered TSH with serum-type glycosylation and compared its immunological behavior to that of the international standards. STUDY DESIGN: Recombinant glycoengineered TSH (rgTSH) was produced in glycoengineered Chinese hamster ovary cells to express a highly sialylated TSH and tested in newly designed assays. Two groups of assays targeting defined epitopes were constructed and TSH levels were estimated in a panel of 84 clinical samples (2.1-22.4 mIU/l) based on the use of the current 3rd IS 81/565, the 1st IRP 94/674 and rgTSH calibrations. RESULTS: Calibration based on rgTSH was found to significantly reduce the percentage difference means of assays compared to the pituitary standard. We also found that a switch from a mIU/l (3rd IS 81/565) to ng/l (rgTSH) basis can be established within the normal as well as in the mid to upper normal range of TSH levels. Of interest, TSH assays targeting the main immunogenic region displayed variable TSH values, indicating that, in this region, epitopes should be defined for assays to deliver similar values. CONCLUSIONS: A glycoengineered TSH with serum-type glycosylation proved to be a new calibrator efficient in harmonizing TSH values.

Serum Sclerostin Increases After Acute Physical Activity.

Physical activity has a major impact on bone density and on osteoporosis prevention. Sclerostin is produced by osteocytes and inhibits bone formation. The impact of exercise on sclerostin secretion has not been studied so far. This pilot study aimed to explore circulating sclerostin levels immediately after acute exercise. Healthy young women practicing physical activity less than 120 min per week were enrolled. The exercise was a 45-min, low-speed, treadmill running test. Blood samples were taken at rest before exercise and within 5 min after the end of exercise. We assessed serum creatinine, 25-OH vitamin D, alkaline phosphatase, C-telopeptide of type I collagen, bone-specific alkaline phosphatase, and sclerostin. Sclerostin stability at rest was also validated over the same period of time among women fulfilling the same inclusion criteria. The study included 23 participants (mean ± SD age: 22.9 ± 1.5 years) for the exercise test and 9 participants for the resting test (26.1 ± 3.1 years). There was no difference in body mass index between the two groups. Sclerostin increased after exercise in comparison to baseline (mean ± SEM: 410 ± 27 vs. 290 ± 19 pg/mL; p < 0.001) corresponding to an increase of +44.3 ±5.5%. In the resting test, sclerostin remained stable (303 ± 20 vs. 294 ± 20 pg/mL, p = 0.76). There was a substantial increase in serum sclerostin in untrained healthy young women immediately after physical activity. These results suggest the existence of an acute release of systemic sclerostin in response to physical activity.

Antibody-Mediated Insulin Resistance: When Insulin and Insulin Receptor Act as Autoantigens in Humans.

We report the case of a patient with diabetes presenting a severe insulin-resistance syndrome due to the production of insulin autoantibodies by a lymphocytic lymphoma. We describe the various mechanisms leading to the production of insulin autoantibodies and insulin receptor autoantibodies and review the therapeutic possibilities.

Neuroendocrine tumors producing calcitonin: characteristics, prognosis and potential interest of calcitonin monitoring during follow-up.

OBJECTIVES: Inappropriate calcitonin (CT) release, a major feature of medullary thyroid cancer (MTC), may occur in neuroendocrine tumors (NETs). The aims of this retrospective study were to assess i) the characteristics and prognosis of CT-producing NETs, and ii) the value of CT monitoring during follow-up. METHODS: All patients with NETs in whom serum CT was assayed between 2010 and 2012 were included. MTCs were excluded. Clinical, biological, and histological characteristics were studied. RESULTS: Twenty-one (12%) of 176 patients in whom serum CT was systematically assayed had concentrations >100  ng/l, with tumours predominantly of bronchial or pancreatic origin (P<0.0001), and of high grade (P=0.0006). Poor prognosis was linked to high CT levels, poor differentiation, and grade 3. In a total group of 24 patients with serum CT >100  ng/l, symptoms potentially attributable to CT were recorded in eight, with occasional overlap with the carcinoid syndrome among other secretory syndromes. Immunohistochemistry could be performed in six tumor specimens, CT being detected in five. In 11 patients with five or more successive CT assays, hormone levels were fairly well correlated with clinical courses. CONCLUSION: Serum CT levels may be raised in some patients with NETs, especially from foregut origin, and of high grade. The suggested value of CT monitoring during follow-up must be confirmed in further studies.

[Hypothyroidism Associated to TSH Hormone-Receptor Autoantibodies with Blocking Activity Assessed In Vitro]. / Hipotiroidismo Associado a Anticorpos Anti-Receptor da Hormona TSH com Ação Bloqueadora Determinada In Vitro.

Thyroid-stimulating hormone-receptor autoantibodies normally causes hyperthyroidism. However, they might have blocking activity causing hypothyroidism. A 11-year-old girl followed due to type 1 diabetes mellitus, celiac disease and euthyroid lymphocytic thyroiditis at diagnosis. Two years after the initial evaluation, thyroid-stimulating hormone was suppressed with normal free T4; nine months later, a biochemical evolution to hypothyroidism with thyroid-stimulating hormone-receptor autoantibodies elevation was seen; the patient remained always asymptomatic. Chinese hamster ovary cells were transfected with the recombinant human thyroid-stimulating hormone -receptor, and then exposed to the patient's serum; it was estimated a 'moderate' blocking activity of these thyroid-stimulating hormone-receptor autoantibodies, and concomitantly excluded stimulating action. In this case, the acknowledgment of the blocking activity of the serum thyroid-stimulating hormone-receptor autoantibodies, supported the hypothesis of a multifactorial aetiology of the hypothyroidism, which in the absence of the in vitro tests, we would consider only as a consequence of the destructive process associated to lymphocytic thyroiditis.

Os anticorpos anti-receptor da hormona estimulante da tiróide causam habitualmente hipertiroidismo. No entanto, a sua atividade pode ser bloqueadora, condicionando o hipotiroidismo. Apresenta-se o caso de uma doente do sexo feminino, 11 anos, com diabetes mellitus tipo 1, doença celíaca e tiroidite linfocítica em eutiroidismo ao diagnóstico. Cerca de dois anos após a avaliação inicial, a hormona estimulante da tiróide apresentava-se suprimida com T4 livre normal. Nove meses depois, a evolução foi para hipotiroidismo notandose concomitantemente elevação dos anticorpos anti-receptor da hormona estimulante da tiróide, mantendo-se a doente sempre assintomática. Células chinese hamster ovary foram transfetadas com o receptor de hormona estimulante da tiróide, e após incubação com o soro da doente, verificou-se uma atividade bloqueadora âmoderadaâ dos anticorpos anti-receptor da hormona estimulante da tiróide, excluindo-se ação estimuladora concomitante. Neste caso, o reconhecimento da ação bloqueadora dos anticorpos anti-receptor da hormona estimulante da tiróide detetados no soro suporta a hipótese de uma etiologia multifatorial para o hipotiroidismo que, na ausência dos testes in vitro, tenderíamos a interpretar unicamente como sequela do processo destrutivo associado à tiroidite linfocítica.

Uncertainty in measurement for 43 biochemistry, immunoassay, and hemostasis routine analytes evaluated by a method using only external quality assessment data.

BACKGROUND: International organizations require from medical laboratories a quantitative statement of the uncertainty in measurement (UM) to help interpret patient results. The French accreditation body (COFRAC) recommends an approach (SH GTA 14 IQC/EQA method) using both internal quality control (IQC) and external quality assessment (EQA) data. The aim of this work was to validate an alternative way to quantify UM using only EQA results without any need for IQC data. This simple and practical method, which has already been described as the long-term evaluation of the UM (LTUM), is based on linear regression between data obtained by participants in EQA schemes and target values. We used it for 43 routine analytes covering biochemistry, immunoassay, and hemostasis fields. METHODS: Data from 50 laboratories participating in ProBioQual (PBQ) EQA schemes over 25 months were used to obtain estimates of the median and 90th percentile LTUM and to compare them to the usual analytical goals. Then, the two UM estimation methods were compared using data from 20 laboratories participating in both IQC and EQA schemes. RESULTS: Median LTUMs ranged from 2.9% (sodium) to 16.3% (bicarbonates) for biochemistry analytes, from 12.6% (prothrombin time) to 18.4% (factor V) for hemostasis analytes when using the mean of all participants, and were around 10% for immunoassays when using the peer-group mean. Median LTUMs were, in most cases, slightly lower than those obtained with the SH GTA 14 method, whatever the concentration level. CONCLUSIONS: LTUM is a simple and convenient method that gives UM estimates that are reliable and comparable to those of recommended methods. Therefore, proficiency testing (PT) organizers are allowed to provide participants with an additional UM estimate using only EQA data and which could be updated at the end of each survey.