Clare Ford

Vitamin D: a negative acute phase reactant.

Objective We evaluated the effect of the systemic inflammatory response (SIR), as provoked by elective orthopaedic surgery, on serum vitamin D [25-(OH)D]. Methods Serum 25-(OH)D, serum vitamin D binding protein (VDBP) and urinary VDBP were measured in 30 patients before and 48-hours after knee or hip arthroplasty. C-reactive protein (CRP) was measured to assess the SIR. Results The mean (SD) CRP increased following surgery [5.0 (5.5) vs 116.0 (81.2) mg/L; P<0.0001] as did urine VDBP/Creatinine ratio [8 (9) vs 20 (25) pg/mmol; p=0.0004]. Serum 25-(OH)D [56.2 (30.3) vs 46.0 (27.6) nmol/L; p = 0.0006] and serum VDBP [334 (43) vs 298 (37) mg/L]; P<0.0001] decreased. Conclusions Serum 25-(OH)D is a negative acute phase reactant, which has implications for acute and chronic inflammatory diseases. Serum 25-(OH)D is an unreliable biomarker of vitamin D status after acute inflammatory insult. Hypovitaminosis D may be the consequence rather than cause of chronic inflammatory diseases.

Between-assay variability of faecal calprotectin enzyme-linked immunosorbent assay kits

Background Faecal calprotectin (f-Cp), a marker of intestinal inflammation, can be used to distinguish between functional and organic bowel disease. F-Cp, following extraction, is commonly quantified using enzyme-linked immunosorbent assays (ELISAs) but there are no data comparing the different f-Cp assays or sample extraction devices. We, therefore, evaluated and compared the performance of the Immunodiagnostik, Bühlmann and Eurospital f-Cp ELISA assays as well as the Roche, Immunodiagnostik and ScheBo Biotech commercial faecal extraction devices. We also briefly report results from a pilot f-Cp external quality assurance (EQA) scheme. Methods Imprecision, linearity, recovery, drift and limit of quantitation of the f-Cp assays were evaluated and between-assay variability assessed. The three commercial sample extraction devices were compared with the manual weighing method. Four faecal samples were distributed as part of a pilot EQA scheme to 15 laboratories using quantitative ELISA f-Cp assays. Results The three f-Cp assays demonstrated adequate intra-/interbatch imprecision, linearity and recovery. The crosscomparison study and EQA data demonstrated that, for the same sample, the Bühlmann assay reports up to 3.8 times higher f-Cp concentrations than the Immunodiagnostik and Eurospital assays. On average, the commercial extraction devices led to a 7.8-28.1% under-recovery of f-Cp in comparison to the manual weighing method. Conclusions Laboratories should be aware of the lack of the assay standardization, as demonstrated by the between-assay variability. A comparison between f-Cp concentrations reported by these assays and clinical markers of disease severity is required in order to determine their diagnostic accuracy. The EQA scheme represents the first available programme for f-Cp.

Spurious hyperkalaemia due to EDTA contamination: common and not always easy to identify

Background To study the detection and prevalence of spurious hyperkalaemia due to potassium ethylenediaminetetra-acetic acid (kEDTA) contamination. Methods In a one-month prospective study, serum EDTA, zinc, calcium, magnesium concentrations and alkaline phosphatase activity were measured in samples with serum potassium ≥6.0 mmol/L. Results Twenty-eight out of 117 hyperkalaemic samples were contaminated with EDTA. Only serum zinc values below the reference range had 100% sensitivity for indicating EDTA contamination, but even at an optimal specificity of 89% at least 12 potentially genuine hyperkalaemic samples would be rejected. Conclusion Spurious hyperkalaemia due to kEDTA contamination is common. Gross kEDTA contamination is obvious by marked unexpected hyperkalaemia, hypocalcaemia, hypomagnesaemia and hypozincaemia. Spurious hyperkalaemia due to low concentrations of kEDTA contamination can only be confidently detected by measurement of serum EDTA.

EDTA sample contamination is common and often undetected, putting patients at unnecessary risk of harm

Background:  Potassium ethylenediaminetetraacetic acid (EDTA) is a sample tube anticoagulant used for many laboratory analyses. Gross potassium EDTA contamination of blood samples is easily recognised by marked hyperkalaemia and hypocalcaemia. However, subtle contamination is a relatively common, often unrecognised erroneous cause of spurious hyperkalaemia. Potassium EDTA contamination may also cause hypomagnesaemia and hypozincaemia. There are, however, no data on the prevalence of EDTA contamination as a cause of hypocalcaemia, hypomagnesaemia and hypozincaemia.

Effect of order of draw of blood samples during phlebotomy on routine biochemistry results

Aim To investigate whether incorrect order of draw of blood samples during phlebotomy causes in vitro potassium ethylenediaminetetraacetic acid EDTA (kEDTA) contamination of blood samples. Methods Serum kEDTA, potassium, calcium, magnesium, alkaline phosphatase, zinc and iron concentrations were measured in blood samples drawn before and after collecting blood into kEDTA containing sample tubes by an experienced phlebotomist using the Sarstedt Safety Monovette system. Results EDTA was undetectable in all samples. The concentrations of other analytes were similar in blood samples drawn before and after collection of the EDTA blood sample. Conclusion Order of draw of blood samples using the Sarstedt Safety Monovette system has no effect on serum biochemistry results, when samples are taken by an experienced phlebotomist.

Hypovitaminosis D and disease: consequence rather than cause?

In their editorial calling for vitamin D to be put into perspective Harvey and Cooper do not consider the possibility, supportive to their view, that hypovitaminosis D is the consequence rather than the cause of disease.1 We recently completed a study showing unequivocally that serum 25-hydroxyvitamin D is a negative acute phase reactant. We measured serum C reactive protein …

Salivary cortisol and cortisone responses to tetracosactrin (synacthen)

Background To establish cutoff values for salivary liquid chromatography tandem mass spectroscopy cortisol and cortisone in defining adequate adrenocortical function during a standard synacthen test. Methods We compared salivary liquid chromatography tandem mass spectroscopy cortisol and cortisone responses to those of serum cortisol measured on the Roche E170 immunoassay analyser and the Abbott Architect i2000 before and 30 min and 60 min following 0.25 mg of intravenous synacthen. Results Correlations of salivary cortisol and cortisone were bimodal and linear, respectively. Based on these correlations, adequate salivary cortisol and cortisone responses to synacthen were extrapolated from a serum cortisol (Roche) cut-off of 550 nmol/L and defined as 15 nmol/L and 45 nmol/L, respectively. The Abbott method correlated well with the Roche but gave results that were about 20% lower than the Roche method. Conclusions Measurement of salivary cortisol and cortisone responses offers an alternative to those of serum cortisol during a synacthen test in the investigation of adrenal hypofunction.

Is there any value in measuring faecal calprotectin in Clostridium difficile positive faecal samples

Markers of intestinal inflammation have been proposed for inclusion in Clostridium difficile diagnostic algorithms. Faecal calprotectin (f-Cp), a sensitive marker of intestinal inflammation, was evaluated for utility in C. difficile diagnosis in the hospital setting. One hundred and twenty C. difficile positive and 99 C. difficile negative faecal samples of hospital-acquired diarrhoea were analysed for f-Cp using a quantitative ELISA. C. difficile positivity was confirmed using ELISAs for either toxins (n = 45) or glutamate dehydrogenase (GDH) with toxin gene confirmation (n = 75). Non-parametric ANOVA (Kruskal-Wallis) was used for data analysis. C. difficile positive samples had higher (P<0.05) median (interquartile range) f-Cp levels; 336 µg g(-1) (208-536) for toxin and 249 µg g(-1) (155-498) for GDH and toxin gene positive compared with 106 µg g(-1) (46-176) for C. difficile and culture-negative faecal samples. Five C. difficile positive samples were f-Cp negative (<50 µg g(-1)). A f-Cp concentration >50 µg g(-1) was 96 % sensitive and 26 % specific for C. difficile, with area under the ROC curve of 0.82. There is no role for f-CP alone in predicting C. difficile infection in hospital-acquired diarrhoea due to its low specificity.

A combined laboratory and field evaluation of the Cholestech LDX and CardioChek PA point-of-care testing lipid and glucose analysers

Background Combined lipid and glucose point-of-care testing (POCT) devices could facilitate widespread population screening for cardiovascular disease (CVD) and diabetes as part of the NHS Vascular Risk Assessment and Management Program (NHS Health Checks). An evaluation of the Cholestech LDX and CardioChek PA POCT analysers was performed in collaboration with the Wolverhampton City Primary Care Trust (PCT). Methods Intra-/inter-batch imprecision, between-analyser variation and the effect of haematocrit and ascorbic acid assay interference were investigated. Accuracy of the POCT capillary whole blood total cholesterol (TC), high-density-lipoprotein cholesterol (HDL-C) and glucose measurements was estimated by comparison with those from the laboratory analysis of paired venous samples. POCT usability and clinical governance were also assessed. Results The LDX exhibited lower intra- and inter-batch imprecision and external quality assessment (EQA) scheme between-analyser variation for the measurement of TC, HDL-C and glucose when compared to the CardioChek. Ascorbic acid negatively interfered in all three assays on both POCT analysers and results reported by the CardioChek were influenced by the specimen haematocrit. The LDX displayed closer agreement with the laboratory methods for the measurement of TC and HDL-C but both the LDX and the CardioChek displayed positive bias for the measurement of glucose. Conclusions POCT has clear advantages for delivering NHS Health Checks over the laboratory-based approach although device performance does differ. Users should also be aware of the potential clinical governance and interference issues associated with these devices.

An automated minimum retest interval rejection rule reduces repeat CRP workload and expenditure, and influences clinician-requesting behaviour

Aims Repeat serum C-reactive protein (CRP) measurements on the same day or on consecutive days are of limited clinical value. Minimum retesting intervals are recommended for managing unnecessary repeat testing. As not previously reported, we studied the effect of minimum retesting interval test rejection on laboratory workload and expenditure and on clinician-requesting behaviour. Methods In a prospective study, we evaluated the effect of an automated 48 h CRP minimum retesting interval rule on inpatient and outpatient CRP workload and costs. Control data on inpatient and outpatient serum urea and electrolytes (UE) workload were collected during the study. Results Over 1 year, there was a 7.0% and 12.3% decrease in CRP requests and CRP tests analysed, respectively, following the introduction of the minimum retesting interval rule when compared to the 1 year baseline period. This equated to an estimated annual reduction in revenue costs of £10 500, but cash savings in consumable costs of £3000. There was no significant change in UE requests. Conclusions We report, for the first time, that automated minimum retesting interval rejection rules as a stand-alone strategy are a cheap and sustainable method for reducing unnecessary repeat CRP tests, resulting in small laboratory cash savings, more efficient use of laboratory resources and standardisation of patient care pathways. The minimum retesting interval rejection rule also altered clinician test-requesting behaviour towards more appropriate requesting.