Biotin supplementation causes erroneous elevations of results in some commercial serum 25-hydroxyvitamin d (25OHD) assays.

The Vitamin D External Quality Assessment Scheme (DEQAS) distributes serum samples globally, on a quarterly basis, to assess participants' performance of specific methods for 25-hydroxyvitamin D (25OHD) and 1,25-dihydroxyvitamin D (1,25-(OH)2D). DEQAS occasionally circulates samples containing high levels of substances found in certain clinical situations e.g. 25-OHD2, 24,25-(OH)2D3, hypertriglyceridemia. The increased availability and use of health supplements containing biotin has led to case reports of assay interference in methods utilizing a biotin-streptavidin detection system. In October 2018, DEQAS included a serum sample (545) containing exogenous biotin (concentration =586 µg/L) which was analyzed by a total of 683 laboratories using 35 different methods. The same serum sample (544) without exogenous biotin was also included in the 5-sample set. All methods (760 laboratories) performed satisfactorily on sample 544 giving an All-Laboratory Trimmed Mean = 50.2 ± 6.5 nmol/L (±SD, CV = 12.9 %). The target value for this sample 544 (& 555) was 47.4 nmol/L as determined by Centers for Disease Control and Prevention (CDC) Atlanta, Georgia using their LC-MS/MS reference method. In contrast, #545 containing the exogenous biotin was reported by only 683 laboratories and gave an All-Laboratory Trimmed Mean = 66.8 ± 37.6 nmol/L (±SD, CV = 56.3 %). As expected, LC-MS/MS methods (143 labs) reported similar results for both 544 = 48.9 ± 4.4 nmol/L (±SD) and 545 = 48.3 ± 4.5 nmol/L (±SD) showing that assays involving chromatographic steps are unaffected by the presence of biotin. Several of the antibody-based assays including Abbott Architect, DiaSorin Liaison, Beckman Unicel and Siemens Centaur are also unaffected by the addition of biotin. Two assays, IDS-iSYS and Roche Total 25OHD, both of which use biotin-streptavidin, exhibit biotin interference yielding values with a significant positive bias for 545 of 102.6 nmol/L ± 78.7 nmol/L (±SD) and 517.8 nmol/L ± 209.8 nmol/L (±SD) respectively. Interestingly, the failure to report sample 545 data from 77 laboratories is due solely to those running Roche Total 25OHD or Roche Vitamin D Total II assays. Given the prevalence of the adversely affected assays (25 % of DEQAS users) and the high volume of 25OHD testing, clinicians using these assays should, where possible, only measure 25OHD when patients are off biotin.

External Quality Assessment of 24,25-dihydroxyvitamin D3 (24,25(OH)2D3) assays.

The discovery that mutations of the CYP24A1 gene are a cause of idiopathic infantile hypercalcemia (IIH) has revived interest in measuring serum 24,25(OH)2D3. Several studies have also suggested that a high 25-hydroxyvitamin D3(25-OHD3):24,25(OH)2D3 ratio might provide additional diagnostic information in the investigation of vitamin D deficiency. Measurement of 24,25(OH)2D3 is necessarily restricted to laboratories with mass spectrometry methods although cross reactivity of the metabolite in immunoassays for 25-OHD is a potential cause of misleading results. The international External Quality Assessment (EQA) scheme for vitamin D metabolites (DEQAS) was set up in 1989. In 2013 DEQAS became an accuracy based EQA for 25-OHD with 'target values' assigned by the National Institute of Standards and Technology (NIST) Reference Measurement Procedure (RMP). A pilot scheme for serum 24,25(OH)2D3 was started in 2015 and participants were asked to measure the metabolite on each of the 5 samples sent out for 25-OHD. Inter-laboratory agreement was poor but this may reflect methodological differences, in particular different approaches to assay standardization. An important potential contribution to reducing variability among assays was the development by NIST of a 24,25(OH)2D3 RMP and its use in assigning values to SRMs 972a, 2973 and 2971, supported by the NIH Office of Dietary Supplements (ODS) as part of the Vitamin D Standardization Program (VDSP) effort.

Best practice in primary care pathology: review 3.

This best practice review examines four series of common primary care questions in laboratory medicine: (i) "minor" blood platelet count and haemoglobin abnormalities; (ii) diagnosis and monitoring of anaemia caused by iron deficiency; (iii) secondary hyperlipidaemia and hypertriglyceridaemia; and (iv) glycated haemoglobin and microalbumin use in diabetes. The review is presented in question-answer format, referenced for each question series. The recommendations represent a précis of guidance found using a standardised literature search of national and international guidance notes, consensus statements, health policy documents and evidence-based medicine reviews, supplemented by Medline Embase searches to identify relevant primary research documents. They are not standards, but form a guide to be set in the clinical context. Most of the recommendations are based on consensus rather than evidence. They will be updated periodically to take account of new information.

Clinical problems in radiotherapy of carcinoma of the pancreas.

Since 1975, 94 patients with localized unresectable carcinoma of the pancreas have been irradiated using helium and heavier particles at the University of California Lawrence Berkeley Laboratory. Despite surgical exploration and an extensive diagnostic workup including radiological, nuclear medicine, and computer-assisted tomographic studies, many patients proved to have occult liver metastases manifested within 9 months post treatment. In addition, local and regional control of the primary neoplasm (approximately 20%) has been difficult to obtain even with doses of 6000 equivalent rad in 7 1/2 weeks. Gastric and biliary obstruction have required surgical bypass procedures since irradiation has not been successful in relieving obstructive symptoms. Evidence of gastrointestinal injury has been present in postradiation therapy in approximately 10% of patients, a figure which might be higher if more patients had a longer survival (average 10 months). Some patients require pancreatic enzyme supplementation because of pancreatic deficiency either secondary to tumor or treatment. Further improvement in local control and survival requires better diagnostic methods for evaluation of local and metastatic spread, improved therapy for local and regional disease, as well as therapy directed at occult liver metastases that are frequently present.

Randomized study of 5-FU and CCNU in pancreatic cancer: report of the Veterans Administration Surgical Adjuvant Cancer Chemotherapy Study Group.

Between the years 1973-1977, 152 male patients from 28 participating Veterans Hospitals with histologically proven nonresectable cancer of the pancreas were randomized in a two-arm study. The treated group was to receive combination chemotherapy with 5-FU and CCNU, and the controls were to receive no chemotherapy. Both groups were comparable with respect to age, amount of weight loss, extent of histologically proved metastases, and operation performed. In the treatment group, drug therapy was begun between 10 and 60 days postoperatively. Intravenous 5-FU, 9 mg/kg, was administered on five consecutive days, and CCNU, 70 mg/m2, was given orally on the first day of each course. In the absence of toxicity, the course was repeated every six weeks for life; 146 drug courses were given. The incidence of toxicity was not great. One or more toxic reactions were reported for one-third of the drug courses administered, but for the most part, these were mild. The most frequent toxic reaction was vomiting in 17% of the courses, and hematologic toxicity-primarily leukopenia-in 15% of the drug courses. There was no evidence of a beneficial effect on survival from drug treatment in the group as a whole or in any subgroup analyzed. The median survival of the control group was 3.9 months, and of the drug-treated group, 3.0 months.