A clinical chemistry analyzer evaluated by NCCLS guidelines for use in a military field laboratory unit

In a previous comparison study of "dry chemistry" desktop analyzers, the ChemPro 1000 (Arden Medical Systems) was one of several instruments found suitable for field use. We have now evaluated the linearity, accuracy, and precision of the ChemPro 1000, according to NCCLS Document EP 10-P. We also compared results with those by the SMAC (Technicon) and the Nova 9 (Nova Biomedical) for electrolytes, serum urea nitrogen, and ionized calcium in field and laboratory environments. The precision (CV) of the ChemPro was within acceptable ranges for dry chemistry desktop analyzers for all analytes tested. This instrument is a suitable and reasonable alternative to manual chemistry or to large, automated instrumentation in a field environment.     

三种检测方法在支原体实验室检测中的差

目的 探讨荧光定量PCR技术、培养-药敏法及单纯培养法在支原体实验室检测中的差别,为临床实验诊断提供依据。 方法 对58例门诊女性患者分别采用荧光定量PCR法、培养-药敏法、单纯培养法检测子宫颈支原体感染情况,分析不同方法对支原体感染结果的影响。 结果 58例样本中实时荧光定量PCR法检测支原体阳性率为39.7%(23/58),培养-药敏法检测支原体阳性率32.8%(19/58),单纯培养法检测支原体阳率19.0%(11/58)。三种检测结果的阳性率比较差异有统计学意义(P0.05)。 结论 三种方法中荧光定量PCR法最有实验室诊断价值。培养-药敏法有较高的临床实用价值。单纯培养法在实验室诊断价值方面比不上前面两种方法,但对设备条件有限的医疗机构仍有一定实用性。     

A note on the use of outlier criteria in Ontario laboratory quality control schemes

OBJECTIVES: This paper examines the pitfalls that arise when an outlier is assessed using a criterion based on a fixed multiple of the standard deviation rather than an established statistical test. Although the former approach is statistically invalid, it is the favored method for identifying outliers in Ontario laboratory quality control protocols. DESIGN AND METHODS: Computer simulations are used to calculate the probability of a false positive result (classifying a valid observation as an outlier) when outlier criteria based on fixed multiples of the standard deviation are applied to samples containing no outliers. RESULTS: The estimated probability of a false positive result is tabulated over various sample sizes. Outlier criteria based on fixed multiples of the standard deviation are shown to be highly inefficient. CONCLUSIONS: This work presents arguments for discontinuing the widespread practice of using outlier criteria based on fixed multiples of the standard deviation to identify outliers in univariate samples.     

感染性疾病实验室诊断方法的Logistic回归分析

目的建立Logistic回归模型,探讨检测C反应蛋白(CRP)、血清淀粉样蛋白A(SAA)及降钙素原(PCT)在感染性疾病鉴别中的诊断价值。方法选取230例病毒感染者、245例细菌感染者和200例健康对照者,采用单因素及多因素分析方法对实验室检测结果进行比较分析,建立感染性疾病诊断方法的Logistic回归模型并绘制ROC曲线。结果感染组与对照组的CRP、SAA、PCT、白细胞计数(WBC)及SAA/CRP差异均有统计学意义(P0.05)。细菌感染组CRP、SAA、PCT、WBC及中性粒细胞百分比(NEU%)水平明显高于病毒感染组和对照组,而病毒感染组血清淋巴细胞百分比(LY%)及SAA/CRP又明显高于细菌感染组(P0.01)。细菌感染组筛选了4项指标进入Logistic回归模型:CRP、SAA、PCT及WBC,其中CRP、SAA和PCT的ROC曲线下面积均超过了0.900;病毒感染组仅SAA与WBC进入Logistic回归模型,其中SAA的ROC曲线下面积为0.859。结论以实验诊断技术建立的Logistic回归模型有利于临床早期鉴别诊断感染性疾病,尤以联合检测SAA和CRP或PCT更有意义。     

The effects of total laboratory automation on the management of a clinical chemistry laboratory. Retrospective analysis of 36 years

BACKGROUND: Thirty-six years of data and history of laboratory practice at our institution has enabled us to follow the effects of analytical automation, then recently pre-analytical and post-analytical automation on productivity, cost reduction and enhanced quality of service. METHODS: In 1998, we began the operation of a pre- and post-analytical automation system (robotics), together with an advanced laboratory information system to process specimens prior to analysis, deliver them to various automated analytical instruments, specimen outlet racks and finally to refrigerated stockyards. By the end of 3 years of continuous operation, we compared the chemistry part of the system with the prior 33 years and quantitated the financial impact of the various stages of automation. RESULTS: Between 1965 and 2000, the Consumer Price Index increased by a factor of 5.5 in the United States. During the same 36 years, at our institution's Chemistry Department the productivity (indicated as the number of reported test results/employee/year) increased from 10,600 to 104,558 (9.3-fold). When expressed in constant 1965 dollars, the total cost per test decreased from 0.79 dollars to 0.15 dollars. Turnaround time for availability of results on patient units decreased to the extent that Stat specimens requiring a turnaround time of <1 h do not need to be separately prepared or prioritized on the system. CONCLUSIONS: Our experience shows that the introduction of a robotics system for perianalytical automation has brought a large improvement in productivity together with decreased operational cost. It enabled us to significantly increase our workload together with a reduction of personnel. In addition, stats are handled easily and there are benefits such as safer working conditions and improved sample identification, which are difficult to quantify at this stage.     

Comparison of results for 13 clinical laboratory determinations with three automated analytical systems.

We evaluated the Abbott Bichromatic Analyzer-100 (ABA-100) for use in the routine clinical chemistry laboratory by examining 13 different determinations that can be performed on the instrument. Results with the Du Pont "aca" and Technicon continuous-flow systems were compared to the ABA-100 in terms of upper limits of linearity, inter-run coefficient of variation, and results for samples from patients. The upper limits of linearity for the methods on the ABA-100 exceeded all of those for the continuous-flow systems, except for urea nitrogen. Precision of the ABA-100 was as good as or better than that of the aca for all determinations, except for glucose in a normal control serum and creatine kinase and creatinine in an above-normal control serum.     

Comparison of three procedures for isolating human ferritin, for use as a standard in an immunoradiometric assay.

We evaluated three methods for isolating ferritin for use as a standard, with respect to purity of the products, ease of preparation, and yield. Examination of the respective products by gel filitration on Sephadex G-200 and Sepharose 6B suggested that the preparations isolated by ammonium sulfate and cadmium sulfate precipitation (Method 1) and by ultracentrifugation (Method 2) were homogeneous, while the product of a procedure including precipitation with ammonium sulfate (Method 3) contained significant amounts of nonferritin protein. The ratios of ferritin as measured by immunoradiometric assay to the amount of protein in the product indicated the ferritin prepared by Method 1 to be the most highly purified. Methods 1 and 2 were both comparatively simple. Although the yield from Method 1 was lowest, it is probably the method of choice, on the basis of the ease of obtaining a highly purified product. The most appropriate method for estimating protein in the isolated preparations appears to be that of Lowry et al.     

Solid phase chemistry in clinical laboratory tests: a literature review

The present review attempts to summarize and discuss the systems based on solid phase chemistry reagent carriers. The development and the principles of the different systems are first discussed, followed by a survey of the literature on different analytes, and a discussion of possible sources of interference in each of the most important commercial systems.     

Comparison of methods for calculating serum osmolality: multivariate linear regression analysis.

BACKGROUND: There are several methods for calculating serum osmolality, and their accordance with measured osmolality is the subject of controversy. METHODS: The concentrations of sodium, potassium, glucose, blood urea nitrogen (BUN) and osmolalities of 210 serum samples were measured. Two empirical equations were deduced for the calculation of serum osmolality by regression analysis of the data. To choose the best equation, chemical concentrations were also used to calculate osmolalities according to our formulas and 16 different equations were taken from the literature and compared with the measured osmolalities. Correlation and linear regression analyses were performed using Excel and SPSS software. RESULTS: Multiple linear regression analysis showed that serum concentrations of sodium (beta = 0.778, p< or = 0.000), BUN (beta = 0.315, p < or = 0.000), glucose (beta = 0.0.089, p < or = 0.007) and potassium (beta = 0.109, p < or = 0.008) are strong predictors of serum osmolality. The data were also analyzed by manual linear regression to yield the equations: osmolality = 1.897[Na + ]+glucose+BUN+13.5, and osmolality = 1.90[Na+ + K+]+glucose+BUN+5.0. The osmotic coefficient for sodium and potassium solutes was deduced to be 0.949 from the slope of the curves of measured osmolality vs. [Na+] and [Na+ + K+], respectively. The inclusion of a BUN value in the equation for osmolality increased the correlation coefficient by approximately 450% and decreased the SD of difference by approximately 35% (p < or = 0.002). Inclusion of the osmotic coefficient for sodium solutes caused an underestimation of measured osmolality and positive osmolal gap unless an appropriate coefficient, constant value and/or the potassium value were included in the equation. The agreement was not improved when molal chemical concentrations were used instead of molar values. The formula presented by Dorwart and Chalmers gave inferior results to those obtained with our formulas. CONCLUSIONS: Our data suggest use of the Worthley et al. formula Osm = 2[Na +]+glucose+BUN for rapid mental calculation and the formulas of Bhagat et al. or ours for calculation of serum osmolality by equipment linked to a computer.     

Segmented regression analysis of interrupted time series studies in medication use research

Interrupted time series design is the strongest, quasi-experimental approach for evaluating longitudinal effects of interventions. Segmented regression analysis is a powerful statistical method for estimating intervention effects in interrupted time series studies. In this paper, we show how segmented regression analysis can be used to evaluate policy and educational interventions intended to improve the quality of medication use and/or contain costs.     

Comparison of procedures for evaluating laboratory performance in external quality assessment schemes for lead in blood and aluminum in serum demonstrates the need for common quality specifications

BACKGROUND: The different scoring methods used by eight European External Quality Assessment Schemes (EQASs) for occupational and environmental laboratory medicine were compared to develop suitable quality specifications as a step toward harmonization. METHODS: Real results for blood lead and serum aluminum assays, reported by participants in Italian and United Kingdom EQASs, were evaluated according to individual scheme scoring criteria. The same results were then used to produce z scores using scheme-based between-laboratory SDs as the estimate of variability to determine whether simple performance-derived quality specifications produced better agreement among schemes. RESULTS: The schemes gave conflicting assessments of participants' performance, and participants judged to be successful by one scheme could be defined as performing inadequately by another. An approach proposed by Kenny et al. (Scand J Clin Lab Invest 1999;59:585), which uses clinical inputs to set targets for analytical imprecision, bias, and total error allowable, was then used to elaborate quality specifications. CONCLUSIONS: We suggest that the CLIA '88 recommendations for blood lead (+/- 40 micro g/L or +/- 10% of the target concentration, whichever is the greater) could be used as a quality specification, although a revision to +/- 30 micro g/L or +/- 10% is recommended. For serum aluminum, a suitable quality specification of +/- 5 micro g/L or +/- 20% of the target concentration, whichever is the greater, is suggested. These specifications may be used to compare laboratory performance across schemes.     

Evaluation of the VITROS 5,1 FS chemistry system in a large pediatric laboratory

The VITROS 5,1 FS analytical system was evaluated. The measurement of the serum proteins and HDL cholesterol with the newly developed MicroTip technology was compared with other nephelometric and turbidimetric methods. The within-run imprecision for apolipoprotein A1, apolipoprotein B, complement 3, complement 4, transferrin, immunoglobulin A, immunoglobulin M, immunoglobulin G and HDL cholesterol showed coefficients of variation between 0.4% and 4.7%. The day-to-day imprecision showed coefficients of variation between 0.5% and 4.0%. The correlation with the comparative methods (nephelometric or turbidimetric) was good, with Pearson correlation coefficients of between 0.959 and 0.995. The comparison of apolipoprotein Al showed a slope of about 0.76. An explanation for the difference could not be found. The VITROS 5,1 FS analytical system is a reliable routine instrument which fits into a large pediatric laboratory of a university.