The effect of the immunoassay curve fitting routine on bias in troponin

OBJECTIVES

Unlike many dose-response curves used in clinical chemistry, the immunoassay curve used to quantitate measurands is often sigmoidal rather than linear. Consequently, a more complex curve fitting model is required. Various models are available, but they can introduce bias, and there can be little awareness of why this error can be introduced.

CONTENT

These curve-fitting models include those based on the law of mass-action, empirical models such as splines or linearization models such as the log/logit function. All these models involve assumptions, which can introduce bias as the dose-response curve is 'forced' to fit or minimize the distance between the standard concentration points to the theoretical curve. The most common curve fitting model is the four or five parameter model, which uses four or five parameters to fit a sigmoidal curve to a set of standard points.

SUMMARY AND OUTLOOK

Measurement of cardiac troponin is an important element in establishing a diagnosis of acute myocardial infarction. We use troponin, a cardiac biomarker, to demonstrate the potential effect of the bias that the curve fit could introduce. Troponin is used for both rule-in and rule-out decisions at different concentrations and at either end of the dose-response curve. The curve fitting process can cause lot-to-lot reagent (and calibrator) variation in immunoassay. However, laboratory staff need to be aware of this potential source of error and why it occurs. Understanding how the error occurs leads to a greater awareness of the importance of validating new reagent/calibrator assessment using patient samples with concentrations at crucial decision points.

Inflammatory Abdominal Aortic Aneurysms

About 10% of all abdominal aortic aneurysms are characterized by an exuberant inflammatory reaction consisting of a dense white sheath over the aneurysm with peri-aortic fibrosis. The aetiology is unknown. There are characteristic ultrasonic and CT appearances but the condition is usually diagnosed at laparotomy. Surgery is the best treatment, keeping peri-aortic dissection to a minimum. Steroid therapy may occasionally be indicated where the situation is considered inoperable or when the patient declines surgery. If hydronephrosis is present because of ureteric involvement, surgical ureterolysis, as for retroperitoneal fibrosis, should be considered.

Harmonising adult and paediatric reference intervals in australia and new zealand: an evidence-based approach for establishing a first panel of chemistry analytes

Scientific evidence supports the use of common reference intervals (RIs) for many general chemistry analytes, in particular those with sound calibration and traceability in place. Already the Nordic countries and United Kingdom have largely achieved harmonised RIs. Following a series of workshops organised by the Australasian Association of Clinical Biochemists (AACB) between 2012 and 2014 at which an evidence-based approach for determination of common intervals was developed, pathology organisations in Australia and New Zealand have reached a scientific consensus on what adult and paediatric intervals we should use across Australasia. The aim of this report is to describe the processes that the AACB and the Royal College of Pathologists of Australasia have taken towards recommending the implementation of a first panel of common RIs for use in Australasia.

Medicare readmission rates showed meaningful decline in 2012

OBJECTIVE

Descriptive analysis of 30-day, all-cause hospital readmission rate patterns from 2007-2012.

POPULATION

Medicare FFS beneficiaries experiencing at least one acute inpatient hospital stay.

METHODS

Using Chronic Condition Data Warehouse claims, we estimate unadjusted, monthly, readmission rates for the nation, within the Dartmouth Hospital Referral Regions (HRR), and compare participating and non-participating hospitals in the Partnership for Patients (P4P) program (overall and by number of inpatient beds at each facility).

RESULTS

From 2007 through 2011, the national 30-day, all-cause, hospital readmission rate averaged 19 percent. During calendar year 2012, the readmission rate averaged 18.4 percent. Of the 306 HRRs, rates in 166 HRRs fell by between 1 and 5 percent, while rates dropped by more than 5 percent in 73 HRRs, with the largest reduction in Longview, Texas. Rates increased by more than 1 percent in only 30 HRRs, with the largest increase in Bloomington, Illinois. Readmission rates at hospitals participating in the P4P program have been, on average, consistently lower than the rates at non-participating hospitals within all size categories except for the very smallest and largest hospitals, but rates at both participant and non-participant hospitals fell in 2012.

DISCUSSION

Although claims data are not yet final for 2012, our analysis indicates that hospital readmission rates for all Medicare FFS beneficiaries dropped noticeably during the year. The reasons behind the apparent reduction are not yet clear and merit further investigation.

The relationship between dosing of alosetron and discontinuation patterns reported by patients participating in a follow-up programme

BACKGROUND

Alosetron was reintroduced for treatment of irritable bowel syndrome with a risk management programme in November 2002. Recommended starting dosage was 1 mg/day for 4 weeks. If symptoms remained uncontrolled, dosage could be changed to 2 mg/day.

AIM

To describe alosetron dosages and associated patient characteristics from the Lotronex follow-up survey programme.

METHODS

Patients reported dosages of alosetron at start and regular follow-up intervals. Analyses were limited to patients with the potential to have at least 1 year of follow-up (enrolled between 9 December 2002 and 31 December 2003).

RESULTS

At baseline, 75% of 2817 respondents reported starting on 1 mg/day, 17% on 2 mg/day and 8% on other doses. Adherence to recommended starting dosage did not vary by status at end of follow-up, previous alosetron experience or age. At last reported dose, 50% of respondents were using 1 mg/day; 29% were using 2 mg/day. Discontinuation was not related to baseline doses. Longer times to discontinuation were associated with previous use, symptoms for more than 6 months and dose change throughout follow-up.

CONCLUSIONS

High adherence to recommended dosing at baseline and follow-up suggests that the risk management programme is encouraging safe use of alosetron, including adherence to dosing recommendations.

Interleukin-8 (IL-8) may contribute to the activation of neutrophils in patients with peripheral arterial occlusive disease (PAOD)

OBJECTIVES

to investigate the levels of interleukin-8 (IL-8) in patients with peripheral arterial occlusive disease (PAOD) and healthy control subjects both before and after an acute exercise test.

MATERIALS AND METHODS

twenty-six patients with intermittent claudication and 22 matched healthy control subjects each had IL-8 levels measured before and after a standard acute treadmill-exercise test. Subjects walked for 10 min or until stopped by claudication pain. Serum IL-8 levels were measured before exercise was commenced and 1, 5 and 10 min after exercise was stopped.

RESULTS

patients with PAOD had statistically significantly higher levels of IL-8 than healthy control subjects, before and after an acute exercise test (p <0.00001, Mann-Whitney). Ratios of the change of IL-8 levels post-exercise showed a statistically significant difference at the post-5-min time point (p =0.005), showing a difference in the change of IL-8 levels at this time point between the patient group and control group.

CONCLUSIONS

The increased levels and the failure of the cytokine levels to fall by the same extent after exercise in the patient group may be due to a combination of increased neutrophil activation, reduced blood flow and increased cytokine production during ischaemia-reperfusion, which is not observed in the healthy controls.

Apolipoprotein E polymorphism in indigenous Australians: allelic frequencies and relationship with dyslipidaemia

OBJECTIVES

To determine the apolipoprotein E (apoE) allelic frequencies and the effect of apoE genotype on lipid concentrations in indigenous Australian subjects.

DESIGN

Cross-sectional study.

SUBJECTS AND SETTING

155 indigenous Australians (92 women and 63 men) of mean (+/- standard deviation) age 45 +/- 17 years (SD +/- 50) were recruited without regard to history of atherosclerotic disease, in collaboration with community-based health centres in five indigenous communities in south-east Queensland. For comparison, 113 subjects of European descent and similar age distribution from the Brisbane and Gold Coast regions were also studied.

MAIN OUTCOME MEASURES

ApoE allelic frequency; apoE genotype; sex; age; diabetes status; body mass index; history of atherosclerotic vascular disease; and concentrations of total cholesterol, triglyceride, HDL-cholesterol and LDL-cholesterol.

RESULTS

The frequency of the apoE4 allele was found to be significantly higher in the indigenous subjects than in the subjects of European descent (P < 0.001). Among indigenous subjects, those with the apoE4 allele tended to have higher triglyceride concentrations and had significantly lower HDL-cholesterol concentrations than those with the apoE3/3 and 3/2 genotypes.

CONCLUSIONS

ApoE allelic frequency is likely to be one of the cluster of factors contributing to the high cardiovascular mortality of indigenous Australians.

Amputation level assessment using lightguide spectrophotometry

The aim of this experimental study was to investigate whether lightguide spectrophotometry in the visible wavelength range in skin could be used to predict stump healing viability in patients with critical lower limb ischaemia. Remission spectra recorded at two sites (medial and lateral) on the line of a proposed trans-tibial amputation (TTA) and at 10mm intervals along the leg were analysed to give haemoglobin oxygenation (SO2). Degree of tissue hypoxia (DTH) along the leg was defined as the percentage of values along the leg less than 10% SO2. DTH and mean SO2 values were compared with skin blood flow values ((I125) 4-Iodoantipyrine clearance technique) and clinical outcome of trans-tibial amputation, (TTA) or trans-femoral amputation (TFA), in 41 patients. SO2 histograms were also measured in 12 normal subjects for comparison. The results of the study allowed the establishment of criteria for the accurate prediction of flap healing potential. Successful TTAs all displayed a minimum mean SO2 at the medial and lateral measurement sites of 30%, together with a maximum degree of tissue hypoxia of 15% along the limb. The combination of these criteria gave a sensitivity and selectivity of 1.0 for prediction of a successful outcome of TTA.

Neutrophils may contribute to the morbidity and mortality of claudicants

Peripheral arterial occlusive disease is a common cause of morbidity in middle-aged men; 5 per cent of those aged over 50 years suffer from intermittent claudication. While claudication itself is not fatal, claudicants have a mortality rate approximately three times that of non-claudicating men of the same age, mainly from cardiovascular disease. This review examines the evidence for involvement of the neutrophil in this increased mortality and describes the possible pathogenesis. It also discusses how treatment of claudication may modify neutrophil behaviour, reducing subsequent mortality and morbidity rates.

Effect of postoperative low-dose dopamine on renal function after elective major vascular surgery

OBJECTIVE

To determine the effect on renal function of postoperative low-dose dopamine in volume-replete patients after elective, major vascular abdominal surgery.

DESIGN

Randomized, double-blind, placebo-controlled trial.

SETTING

Intensive care unit of a referral hospital in Brisbane, Australia.

PATIENTS

37 patients having elective repair of an abdominal aortic aneurysm or having aortobifemoral grafting; 18 received dopamine, and 19 received placebo. Two patients were excluded from the 5-day analysis because of perioperative death.

INTERVENTIONS

Patients were randomly assigned to receive either placebo or a low-dose infusion of dopamine (3 micrograms/kg per minute) in saline. Patients in both groups were given sufficient crystalloid to maintain a urine flow of more than 1 mL/kg per hour during the first 24 postoperative hours. Care in the intensive care unit was otherwise usual and was the same for each group.

MEASUREMENTS

Plasma creatinine levels, urea levels, and creatinine clearance were measured preoperatively and postoperatively (at 24 hours and 5 days). Urine flow and the volume of crystalloid during the first 24 hours were recorded.

RESULTS

Two postoperative deaths occurred in the dopamine group (from renal failure and myocardial infarction). Four patients had myocardial infarction, three of whom received dopamine. Plasma creatinine levels remained unchanged in both groups. At 24 hours, the mean plasma urea level decreased by 1.07 mmol/L in the dopamine group compared with 1.84 mmol/L in the placebo group, a difference of 0.77 (95% CI, -0.12 to 1.67). The mean 24-hour creatinine clearance increased by 0.165 mL/s (9.89 mL/min) in the dopamine group and by 0.199 mL/s (11.98 mL/min) in the placebo group (P > 0.2). Urine volumes were slightly higher in those receiving dopamine (1.83 mL/kg compared with 1.6 mL/kg, a difference of 0.23 [CI, -0.18 to 0.64]). None of these differences were statistically or clinically significant.

CONCLUSIONS

Within the limits of the small size of the study, low-dose dopamine appeared to offer no advantage to euvolemic patients after elective abdominal aortic surgery. However, patients with acute oliguric renal failure were not included in the study.

The white blood cell and peripheral arterial disease

Peripheral arterial obstructive disease (PAOD) is a common cause of morbidity in middle aged men with 5% of men, over 50 years, suffering from intermittent claudication. Claudication itself does not cause death but claudicants have a mortality three times that expected, mainly from cardiovascular disease. The white blood cell has recently been implicated in the pathogenesis of PAOD. This article will examine the evidence for the involvement of the neutrophil in this increased mortality and describe the possible pathogenesis. It is possible that treatment of claudication could modify white cell responses, reducing subsequent mortality and morbidity.

Is mammographic microcalcification of biological significance?

Mammographic microcalcification is a feature of a proportion of breast cancers. Its occurrence does not appear to be significantly associated with age or primary tumour size. Lymph node involvement by tumour is present in 50% of patients with mammographic microcalcification in relation to the primary tumour, but only 24% of patients without microcalcification. A significantly larger number of lymph nodes (61 of 241 nodes) are involved with tumour in patients with, in comparison to those without (59 of 476 nodes) microcalcification (P < 0.001, chi 2 test). These differences suggest a biologically significant role for the deposition of calcium in microcalcifications, which may relate to the process of tumour cell metastasis. This may be of importance in the assessment of patients with cancers which demonstrate microcalcification on mammography.

Job achievements of Indian and non-Indian graduates in public health: how do they compare?

A graduate education program in public health for American Indians was introduced in the fall of 1971 at the College of Public Health, University of Oklahoma Health Sciences Center. The program was initiated with support from the Office of Economic Opportunity. Between August 1, 1971, and December 31, 1983, 52 American Indians received public health degrees from the University of Oklahoma's College of Public Health. Of that number, 50 received masters degrees in public health; 1 a PhD; and 1 a DrPH degree. Degrees were granted in these disciplines: biostatistics, epidemiology, environmental health, health administration, health education, and human ecology. This study assesses the job achievements of 51 of those American Indian graduates. Each Indian was paired with a non-Indian graduate randomly selected from a cluster sample compiled from the school's files of non-Indian graduates. The results of this study showed that Indian graduates had the kinds and amounts of responsibilities, with the exception of budget approval responsibility, that one would acquire or expect to acquire in a key administrative or staff position. The study further indicated that Indian graduates were generally achieving as much success and satisfaction in their jobs as the non-Indian graduates.