Background: Assays for cardiac troponin (cTn) have undergone improvements in sensitivity and precision in recent years. Increased rates of outliers, however, have been reported on various cTn platforms, typically giving irreproducible, falsely higher results. We aimed to evaluate the outlier rate occurring in patients with elevated cTnI using a contemporary and high-sensitivity assay. Methods: All patients with elevated cTnI (up to 300 ng/L) performed over a 21-month period were assayed in duplicate. A contemporary assay (Abbott STAT Troponin-I) was used for the first part of the study and subsequently a highsensitivity assay (Abbott STAT High-Sensitive Troponin-I) was used. Outliers exceeded a calculated critical difference (CD) (CD ¼ z ¡2  SD Analytical ) where z ¼ 3.5 (for probability of 0.0005) and critical outliers also were on a different side of the decision level. Results: The respective outlier and critical outlier rates were 0.22% and 0.10% for the contemporary assay (n ¼ 4009) and 0.18% and 0.13% for the high-sensitivity assay (n ¼ 3878). There was no significant reduction in outlier rate between the two assays ( 2 ¼ 0.034, P ¼ 0.854). Fifty-six percent of outliers occurred in samples where cTn was an 'add-on' test (and was stored and refrigerated prior to assay). Conclusion: Despite recent improvements in cTn methods, outliers (including critical outliers) still occur at a low rate in both a contemporary and high-sensitivity cTnI assay. Laboratory and clinical staff should be aware of this potential analytical error, particularly in samples with suboptimal sample handling such as add-on tests.
There is concordance between the indications for treatment of paracetamol deliberate self-poisoning based on plasma and saliva paracetamol levels. Saliva paracetamol levels are typically higher than plasma levels. Further studies involving larger numbers of patients, comparing plasma and saliva paracetamol levels in patients with potentially toxic plasma paracetamol concentrations, would be useful in determining the potential clinical value of this method.
Time-of-flight mass spectrometry is a novel procedure for diagnosing familial dysalbuminaemic hyperthyroxinaemia. The test is rapid (<10 min), can be performed on <2 μL of serum and requires minimal sample preparation.
Background: In the laboratory evaluation of suspected paracetamol poisoning, a non-invasive sample type that avoids venepuncture would be an attractive alternative to plasma, particularly in the paediatric setting. Salivary paracetamol measurement has not previously been evaluated in the published medical literature in the setting of deliberate self-poisoning (DSP). Methods: In-house validation experiments (recovery, stability and lower limit-of-detection) were performed on pooled saliva samples using a Roche Acetaminophen assay on a Roche/Hitachi 917 analyser. A clinical study of comparison of paired saliva and plasma samples was also conducted involving adult patients presenting with DSP of paracetamol, the results of which were published previously. Results: The validation experiments using pooled saliva samples showed: (i) mean recovery ( paracetamol concentration 37.5-525 mg/L) 100.01% (+0.02 SD); (ii) precision of repeated assay over 24-h period CV ,4%; (iii) lower limit-of-detection 0.9 mg/L. The clinical study of 21 patients with mean plasma paracetamol concentration of 48 mg/L (range 0 -130) and mean saliva concentration 62 mg/L (range 0 -183) showed good correlation between saliva and plasma concentrations (r 2 ¼ 0.91).
Background: Australian guidelines on the diagnosis of diabetes mellitus (DM) recommend performing an oral glucose tolerance test (OGTT) in people with fasting plasma glucose (FPG) values of 5.5 -6.9 mmol/L. Aim: To evaluate indications, outcomes and confounding factors of OGTTs performed at a large teaching hospital and to compare them with Australian DM guidelines. Method: A retrospective audit of OGTTs performed over an 18-month period in a teaching hospital in a major Australian city. Information gathered included co-morbidities; medications; risk factors for type 2 DM; indication for OGTT; results of OGTT and previous glucose tests. Results: All 129 OGTTs identified were included in the audit. Eighty-nine (69%) were male, with a median age of 57 years (range 19-86), and 3% were of Australian Aboriginal ethnicity. An indication for OGTT was identified in 93%, including FPG 5.5-6.9 mmol/L (36%) and random plasma glucose (RPG) 5.5-11.0 mmol/L (19%). Other indications for OGTT identified included polycystic ovary syndrome or metabolic syndrome (8%), peripheral neuropathy (3%) and as part of a research protocol (12%). Forty-two (35%) were inpatients at the time of OGTT, of which 35 (30%) were admitted for acute medical or surgical illnesses such as stroke. Nineteen percent were taking medications known to affect plasma glucose (e.g. oral corticosteroids). Conclusion: Only 55% of OGTTs had a previous FPG or RPG value warranting OGTT using current Australian DM guidelines. Other valid indications for OGTT were identified in the majority of the remainder. In addition, 41% were performed in the presence of confounding factors (such as acute illness or medications known to affect plasma glucose). Many of the OGTTs that are currently being performed are in the presence of confounding factors that could cause misleading results.
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