The effect of biotin interference on the results of blood hormone assays.

Approximately 70% of medical decisions are made based on results of laboratory investigations. Immunochemical methods are used most commonly in routine laboratory diagnostics of endocrine disorders. Those methods are limited by susceptibility of the immunochemical reaction to various interferences. Interference may be caused by the presence of autologous antibodies, heterophilic antibodies, or paraproteins in the blood serum, by cross-reactions with similar reagents, haemolysis, significant lipidaemia, or hyperbilirubinaemia. Some recent reports have indicated a significant effect of biotin on the reliability of laboratory investigations. Biotin is a water-soluble vitamin belonging to the B group. It is present in popular dietary supplements - alone or as a component of multi-vitamin formulas - and it is advertised as a remedy to falling out and fragility of hair and nails. Due to its low molecular weight and a strong affinity to streptavidin, biotin is used in many immunochemical tests. Due to a strong and stable bond of streptavidin and biotin, analytical methods using the streptavidin (avidin)-biotin system are characterised by superior sensitivity, and they allow determination of very low levels of the tested substance in biological material. The presence of exogenous biotin in a sample may cause interference when using tests that utilise the streptavidin (avidin)-biotin system. Interference of biotin with immunochemical tests depends on several factors: the construction of the immunochemical test, the dose used by the patient, the biotin concentration in the sample, and most of all - the time from the last dose to the collection of biological material for laboratory testing. In this paper we present some practical recommendations and a procedure to be followed in the case of suspected interference of biotin in immunochemical assays, for clinicians and laboratory diagnosticians.

Evaluation of continuous glucose monitoring system for detection of alterations in glucose homeostasis in pediatric patients with ß-thalassemia major.

BACKGROUND: Disturbances of glucose metabolism are common in ß-thalassemia major (ß-TM). AIM: This study was conducted to assess the pattern of glucose homeostasis in pediatric ß-TM patients comparing oral glucose tolerance test (OGTT) and continuous glucose monitoring system (CGMS). METHODS: Two-hundred ß-TM patients were studied and those with random blood glucose (RBG) ≥7.8 mmol/L (140 mg/dL) were subjected to OGTT, insertion of CGMS and measurement of fasting C peptide, fasting insulin, and hemoglobin A1c (HbA1c). RESULTS: Twenty patients (10%) had RBG ≥ 7.8 mmol/L. Using OGTT, 6 out of 20 patients (30%) had impaired glucose tolerance (IGT) while 7 (35%) patients were in the diabetic range. CGMS showed that 7/20 (35%) patients had IGT and 13 (65%) patients had diabetes mellitus (DM); 10 of the latter group had HbA1c readings within diabetic range. The percentage of diabetic patients diagnosed by CGMS was significantly higher than that with OGTT (P = 0.012). Serum ferritin was the only independent variable related to elevated RBG. All ß-TM patients with DM were non-compliant to chelation therapy. CONCLUSIONS: The use of CGMS in the diagnosis of early glycemic abnormalities among pediatric patients with ß-TM appears to be superior to other known diagnostic modalities.

Diagnostic procedure in suspected Graves' disease.

Diagnostic procedure in suspected Graves' disease has never been studied scientifically and actual practice seems quite variable, notably between countries. Recommendations are few and weak (expert opinion). This article presents the recommendations of an expert consensus meeting organized by the French Society of Endocrinology in 2016. In case of clinically suspected thyrotoxicosis, the first-line biological assessment is of thyroid-stimulating hormone (TSH). Free T4 and possibly free T3 assays assess biological severity and are necessary for treatment efficacy monitoring. Positive diagnosis of Graves' disease after biological confirmation of thyrotoxicosis does not always require complementary etiological examinations if clinical presentation is unambiguous, notably including extra-thyroid signs. Otherwise, first-line anti-TSH-receptor (TSH-R) antibody screening is recommended for its good intrinsic performance (sensitivity and specificity) and ease of access in France. Scintigraphy is reserved to rare cases of Graves' disease with negative antibody findings or when another etiology is suspected. Thyroid ultrasound scan may be contributive, but is not recommended in first line.

Newborn Screening for Primary Congenital Hypothyroidism: Estimating Test Performance at Different TSH Thresholds.

Context: Active surveillance of primary congenital hypothyroidism (CH) in a multiethnic population with established newborn bloodspot screening. Objective: To estimate performance of newborn screening for CH at different test thresholds and calculate incidence of primary CH. Design: Prospective surveillance from June 2011 to June 2012 with 3-year follow-up of outcomes. Relative likelihood ratios (rLRs) estimated to compare bloodspot TSH test thresholds of 6 mU/L and 8 mU/L, with the nationally recommended standard of 10 mU/L for a presumptive positive result. Setting: UK National Health Service. Patients: Clinician notification of children aged <5 years investigated following clinical presentation or presumptive positive screening result. Main Outcome Measure(s): Permanent primary CH status determined by clinician report of continuing T4 requirement at 3-year follow-up. Results: A total of 629 newborns (58.3% girls; 58.7% white ethnicity) were investigated following presumptive positive screening result and 21 children (52.4% girls; 52.4% white) after clinical presentation; 432 remained on treatment at 3-year follow-up. Permanent CH incidence was 5.3 (95% CI, 4.8 to 5.8) per 10,000 infants. With use of locally applied thresholds, sensitivity, specificity, and positive predictive value were 96.76%, 99.97%, and 66.88%, respectively. Compared with a TSH threshold of 10 mU/L, positive rLRs for 8 mU/L and 6 mU/L were 1.20 (95% CI, 0.82 to 1.75) and 0.52 (95% CI, 0.38 to 0.72), and negative rLRs were 0.11 (95% CI, 0.03 to 0.36) and 0.11 (95% CI, 0.06 to 0.20), respectively. Conclusions: Screening program performance is good, but a TSH threshold of 8 mU/L appears superior to the current national standard (10 mU/L) and requires further evaluation. Further research should explore the implications of transient CH for screening policy.

Interpretation of plasma PTH concentrations according to 25OHD status, gender, age, weight status, and calcium intake: importance of the reference values.

CONTEXT: Reference values for plasma PTH assessment were generally established on small samples of apparently healthy subjects, without considering their 25-hydroxyvitamin D (25OHD) status or other potential modifiers of PTH concentration. OBJECTIVE: Our objective was to assess ranges of plasma PTH concentration in a large sample of adults, stratifying by 25OHD status, age, gender, weight status, and calcium intake. DESIGN, SETTING, AND PARTICIPANTS: This cross-sectional survey is based on 1824 middle-aged Caucasian adults from the Supplémentation en Vitamines et Minéraux Antioxydants study (1994). MAIN OUTCOME MEASURES: Plasma PTH and 25OHD concentrations were measured by an electrochemoluminescent immunoassay. Extreme percentiles of plasma PTH concentrations were assessed specifically in subjects who had plasmatic values of 25OHD of 20 ng/mL or greater and 30 ng/mL or greater. RESULTS: Among subjects with 25OHD status of 20 ng/mL or greater, the 97.5th percentile of plasma PTH concentration was 45.5 ng/L. By using this value as a reference, 5% of the subjects with plasma 25OHD less than 20 nmol/L had a high plasma PTH level, reflecting secondary hyperparathyroidism. Among vitamin D-replete subjects (25OHD status of 20 ng/mL or greater), the 97.5th percentile of plasma PTH was higher in overweight/obese subjects (51.9 vs 43.5 ng/L among normal weight subjects). CONCLUSIONS: The reference value for plasma PTH defined in this vitamin D-replete population was far below the value currently provided by the manufacturer (65 ng/L) and varied according to overweight status. These results may contribute to improve the diagnosis of primary and secondary hyperparathyroidism and subsequent therapeutic indication.

Variability and reproducibility of circulating vitamin D in a nationwide U.S. population.

CONTEXT: Most studies examining associations between circulating vitamin D and disease are based on a single measure of vitamin D, which may not reflect levels over time, particularly because vitamin D concentrations vary by season. Few studies evaluated how well multiple 25-hydroxyvitamin D [25(OH)D] measures track within the same individual over time. OBJECTIVE: This study examined variability and reproducibility of vitamin D by evaluating repeat measurements of plasma 25(OH)D concentrations while accounting for determinants of circulating concentrations including dietary supplement use and latitude of residence from a population of U.S. radiologic technologists. DESIGN AND PARTICIPANTS: We analyzed circulating 25(OH)D in blood samples taken from 538 men and women from a prospective, nationwide study at two time points within a 1-yr period, most measured in different seasons. Inter- and intra-individual variability, reliability coefficients, and measurement error were examined. RESULTS: The spearman rank correlation between two measurements of 25(OH)D concentrations was moderate (r = 0.75, P < 0.001) and did not vary significantly by participant characteristics including age, race, or latitude. The intraclass correlation coefficient was 0.72 (95% confidence interval = 0.68-0.76). The deattenuation factor of plasma 25(OH)D levels was 1.39, suggesting that a single measure of vitamin D on a continuous scale in regression analyses may result in attenuated relationships of about 40%. CONCLUSION: Our results suggest that a single blood sample obtained in spring or fall provides a reasonable average for 25(OH)D over a 1-yr period, but additional studies are needed to estimate variability and agreement in plasma 25(OH)D measurements over longer intervals and younger populations.

A clinical prediction score to diagnose unilateral primary aldosteronism.

CONTEXT: Adrenal venous sampling is recommended to assess whether aldosterone hypersecretion is lateralized in patients with primary aldosteronism. However, this procedure is invasive, poorly standardized, and not widely available. OBJECTIVE: Our goal was to identify patients' characteristics that can predict unilateral aldosterone hypersecretion in some patients who could hence bypass adrenal venous sampling before surgery. DESIGN AND SETTING: A cross-sectional diagnostic study was performed from February 2009 to July 2010 at a single center specialized in hypertension care. PATIENTS: A total of 101 consecutive patients with primary aldosteronism who underwent adrenal venous sampling participated in the study. The autonomy of aldosterone hypersecretion was assessed with the saline infusion test. INTERVENTION: Adrenal venous sampling was performed without ACTH infusion but with simultaneous bilateral sampling. MAIN OUTCOME MEASURES: Variables independently associated with a lateralized adrenal venous sampling in multivariate logistic regression were used to derive a clinical prediction rule. RESULTS: Adrenal venous sampling was successful in 87 patients and lateralized in 49. All 26 patients with a typical Conn's adenoma plus serum potassium of less than 3.5 mmol/liter or estimated glomerular filtration rate of at least 100 ml/min/1.73 m2 (or both) had unilateral primary aldosteronism; this rule had 100% specificity (95% confidence interval, 91-100) and 53% sensitivity (95% confidence interval, 38-68). CONCLUSIONS: If our results are validated on an independent sample, adrenal venous sampling could be omitted before surgery in patients with a typical Conn's adenoma if they meet at least one of two supplementary biochemical characteristics (serum potassium<3.5 mmol/liter or estimated glomerular filtration rate ≥100 ml/min/1.73 m2).