Reference-mean-centered statistical quality control.

Background: Statistical quality control (SQC) procedures generally use rejection limits centered on the stable mean of the results obtained for a control material by the analyzing instrument. However, for instruments with significant bias, re-centering the limits on a different value could improve the control procedures from the viewpoint of patient safety. Methods: A statistical model was used to assess the effect of shifting the rejection limits of the control procedure relative to the instrument mean on the number of erroneous results reported as a result of an increase in the systematic error of the measurement procedure due to an out-of-control condition. The behaviors of control procedures of type 1ks (k = 2, 2.5, 3) were studied when applied to analytical processes with different capabilities (σ = 3, 4, 6). Results: For measuring instruments with bias, shifting the rejection limits in the direction opposite to the bias improves the ability of the quality control procedure to limit the risk posed to patients in a systematic out-of-control condition. The maximum benefit is obtained when the displacement is equal to the bias of the instrument, that is, when the rejection limits are centered on the reference mean of the control material. The strategy is sensitive to error in estimating the bias. Shifting the limits more than the instrument's bias disproportionately increases the risk to patients. This effect should be considered in SQC planning for systems running the same test on multiple instruments. Conclusions: Centering the control rule on the reference mean is a potentially useful strategy for SQC planning based on risk management for measuring instruments with significant and stable uncorrected bias. Low uncertainty in estimating bias is necessary for this approach not to be counterproductive.

Selecting Statistical Quality Control Procedures for Limiting the Impact of Increases in Analytical Random Error on Patient Safety.

BACKGROUND: QC planning based on risk management concepts can reduce the probability of harming patients due to an undetected out-of-control error condition. It does this by selecting appropriate QC procedures to decrease the number of erroneous results reported. The selection can be easily made by using published nomograms for simple QC rules when the out-of-control condition results in increased systematic error. However, increases in random error also occur frequently and are difficult to detect, which can result in erroneously reported patient results. METHODS: A statistical model was used to construct charts for the 1ks and X/χ2 rules. The charts relate the increase in the number of unacceptable patient results reported due to an increase in random error with the capability of the measurement procedure. They thus allow for QC planning based on the risk of patient harm due to the reporting of erroneous results. RESULTS: 1ks Rules are simple, all-around rules. Their ability to deal with increases in within-run imprecision is minimally affected by the possible presence of significant, stable, between-run imprecision. X/χ2 rules perform better when the number of controls analyzed during each QC event is increased to improve QC performance. CONCLUSIONS: Using nomograms simplifies the selection of statistical QC procedures to limit the number of erroneous patient results reported due to an increase in analytical random error. The selection largely depends on the presence or absence of stable between-run imprecision.

Selecting Statistical Procedures for Quality Control Planning Based on Risk Management.

BACKGROUND: According to the traditional approach to statistical QC planning, the performance of QC procedures is assessed in terms of its probability of rejecting an analytical run that contains critical size errors (PEDC). Recently, the maximum expected increase in the number of unacceptable patient results reported during the presence of an undetected out-of-control error condition [Max E(NUF)], has been proposed as an alternative QC performance measure because it is more related to the current introduction of risk management concepts for QC planning in the clinical laboratory. METHODS: We used a statistical model to investigate the relationship between PEDC and Max E(NUF) for simple QC procedures widely used in clinical laboratories and to construct charts relating Max E(NUF) with the capability of the analytical process that allow for QC planning based on the risk of harm to a patient due to the report of erroneous results. RESULTS: A QC procedure shows nearly the same Max E(NUF) value when used for controlling analytical processes with the same capability, and there is a close relationship between PEDC and Max E(NUF) for simple QC procedures; therefore, the value of PEDC can be estimated from the value of Max E(NUF) and vice versa. QC procedures selected by their high PEDC value are also characterized by a low value for Max E(NUF). CONCLUSIONS: The PEDC value can be used for estimating the probability of patient harm, allowing for the selection of appropriate QC procedures in QC planning based on risk management.

Evaluation of PSA testing by general practitioners: regional study in the autonomic Community of Valencia.

OBJECTIVES: The aim of the study is to compare the use of PSA testing among general practitioners (GPs). METHODS: The number of PSA tests ordered by general practitioners in the years 2008-2009 was examined in a cross-sectional study of nine health districts of Spain. The percentage of PSA ordered to men younger than 50 (PSA<50/PSAtotal) and 40 years (PSA<40/PSAtotal) was calculated. The percentage of men over 50 years who were attended was also calculated and this data was compared with the number of PSA ordered to this population. For two of the departments, these data were also compared between GPs and urologists. RESULTS: PSA testing in 2009 is higher than 2008 in seven health districts. PSA testing in men younger than 50 years was increased along the period of the study and in men younger than 40 years remained steady. The differences between the values of the indicators for urologists and GPs are significant. CONCLUSIONS: The number of PSA tests and the percentage performed to men younger 50 years has been increasing and the variability is high. These data are suggestive for interventions focused on PSA testing and prostate cancer screening in primary care settings.

[The association between bronchiectasis, systemic inflammation, and tumor necrosis factor alpha]. / Bronquiectasias, inflamación sistémica y factor de necrosis tumoral alfa: factores asociados.

OBJECTIVE: The relationship between systemic inflammation and different measures of bronchiectasis severity has not been described. The objective of this study was to analyze the relationship between plasma concentrations of tumor necrosis factor alpha (TNF-alpha), as a marker of systemic inflammation, and some commonly used criteria for quantifying bronchiectasis severity in clinically stable patients whose disease was not caused by cystic fibrosis. PATIENTS AND METHODS: Sixty-eight clinically stable patients with bronchiectasis and 19 age- and sex-matched healthy control subjects were included in the study. Data on disease history, symptoms, severity, functional variables, sputum volume, and microbiological cultures, laboratory findings, and other indicators of disease course were collected. Plasma concentrations of TNF-alpha were measured using high-resolution enzyme-linked immunoabsorbent assay. RESULTS: Plasma concentrations of TNF-alpha were higher in patients than controls (8.28 vs 5.67 pg/mL; P=.001). This observation correlated with other markers of systemic inflammation such as erythrocyte sedimentation rate (r=0.42; P=.001), C-reactive protein (rho=0.45; P=.001), and percentage of peripheral blood neutrophils (rho=0.45; P=.001). Patients with high plasma concentrations of TNF-alpha (>8.1 pg/dL) had more severe disease (5.19 vs 3.21; P=.001), were more likely to have respiratory failure (37.5% vs 8.3%; P=.003), and a higher rate of Pseudomonas aeruginosa colonization (34.3% vs 8.3%; P=.008). CONCLUSIONS: High plasma concentrations of TNF-alpha were associated with several criteria usually used to assess severity of bronchiectasis in clinically stable patients with disease not caused by cystic fibrosis.

[Bronchiectasis in the elderly. Study of serum levels of immunoglobulin G subclasses]. / Bronquiectasias en pacientes mayores de 65 años. Estudio de los valores séricos de las subclases de inmunoglobulina G.

BACKGROUND AND OBJECTIVE: To analyze the serum levels of immunoglobulin G (IgG) subclasses in a broad range of elderly patients with bronchiectasis. PATIENTS AND METHOD: Data were collected from all patients who had a high-resolution chest computerized axial tomography diagnosis of bronchiectasis in our center. We gathered data related to case history, respiratory symptoms, forced spirometry, general laboratory tests, immunoglobulin concentration (including IgG subclasses), Mantoux test, sputum culture and staining, paranasal sinus X-rays/computerized axial tomography, and a specific etiologic evaluation based on the available clinical evidence. RESULTS: A total of 128 patients were included -mean age (standard deviation): 71.6 (5.1) years; range: 65-88; 44.5% males- and 20.3% of them had chronic sputum colonization with Pseudomonas aeruginosa. 28.1% cases had a post-infectious nature and in 40.6% the etiology was unknown. Sixteen patients (12.5%) had decreased levels of at least one of the sIgG compared to normal values. The most frequent deficiency corresponded to IgG2 levels. These subjects showed a characteristic profile of bronchiectasis with an increased lung extension of the disease (p = 0.02); greater presence of cylindrical and diffuse bronchiectasis (p = 0.02 and 0.01, respectively), greater percentage of an unknown etiology (p = 0.004); greater presence of paranasal sinus X-ray abnormalities (p = 0.004) and increased number of past repeated upper airway infections (p = 0.03). CONCLUSIONS: Decreased serum levels of IgG subclasses might be associated with a characteristic profile of bronchiectasis in elderly patients in whom other etiologies have been ruled out.

[An evaluation of glycosylated hemoglobin requesting patterns in a primary care setting: a pilot experience in the Valencian Community (Spain)]. / Evaluación del patrón de solicitud de hemoglobina glucosilada por Atención Primaria: estudio piloto regional en la Comunidad Valenciana.

OBJECTIVE: To assess the pattern of glycosylated hemoglobin (HbA(1c)) requests by clinicians from eight health departments by calculating indicators of demand appropriateness. METHODS: A cross-sectional study of the number of HbA(1c) requests by primary care clinics in 2008 and 2009. The indicator of demand appropriateness was the proportion of HbA(1c) values lower than 6.5%. Variables were collected and indicators were automatically calculated. The number of HbA(1c) measurements that should theoretically have been requested according to known diabetes prevalence data was also calculated. RESULTS: A progressive increase was seen in demand for HbA(1c) measurements. Approximately 54% of HbA(1c) values obtained in seven of the eight departments studied were lower than 6.5%. The number of theoretical HbA(1c) requests that would have been expected based on the known prevalence of diabetes was higher than the number of HbA(1c) requests in all departments. CONCLUSION: The results appear to suggest that HbA(1c) requests by the health departments studied were not always appropriate. HbA(1c) measurements were probably overused in patients without diabetes and underused in patients with diabetes.

Regional variations in test requiring patterns of general practitioners in Spain.

OBJECTIVE: To analyze the requesting patterns for a range of laboratory tests ordered in 2009 from eight laboratories providing services to eight health areas, using appropriate indicators. DESIGN: Indicators measured every test request per 1,000 inhabitants, and indicators that measured the number of tests per related test requested by general practitioners were calculated. The savings generated, if each Health Care Department achieved the appropriate indicator standard, were also calculated. Laboratory Information System registers were collected, and indicators were calculated automatically in each laboratory using a data warehouse application. RESULTS: There was a large difference in demand for tests by health areas. The ratio of related tests also showed a great variability. The savings generated if each Health Care Department had achieved the appropriate indicator standard were €172,116 for free thyroxine, €18,289 for aspartate aminotransferase, and €62,678 for urea. CONCLUSIONS: Considerable variability exists in general practitioners' demand for laboratory tests.