Understanding Bland Altman analysis

In a contemporary clinical laboratory it is very common to have to assess the agreement between two quantitative methods of measurement. The correct statistical approach to assess this degree of agreement is not obvious. Correlation and regression studies are frequently proposed. However, correlation studies the relationship between one variable and another, not the differences, and it is not recommended as a method for assessing the comparability between methods. In 1983 Altman and Bland (B&A) proposed an alternative analysis, based on the quantification of the agreement between two quantitative measurements by studying the mean difference and constructing limits of agreement. The B&A plot analysis is a simple way to evaluate a bias between the mean differences, and to estimate an agreement interval, within which 95% of the differences of the second method, compared to the first one, fall. Data can be analyzed both as unit differences plot and as percentage differences plot. The B&A plot method only defines the intervals of agreements, it does not say whether those limits are acceptable or not. Acceptable limits must be defined a priori, based on clinical necessity, biological considerations or other goals. The aim of this article is to provide guidance on the use and interpretation of Bland Altman analysis in method comparison studies

Determination of reference interval for presepsin, an early marker for sepsis

Introduction: Presepsin, the circulating soluble form of CD14 subtype (sCD14-ST) is a new emerging early marker for sepsis. Various cutoff levels of presepsin have been proposed, to discriminate between systemic bacterial and nonbacterial infectious diseases. The aim of this work was to define the reference interval for presepsin according to the CLSI C28-A3c approved guideline. Materials and methods: Reference individuals (N = 200; 120 females) aged 18-75 years (median 39 years), free from inflammatory diseases, were selected for the study. Presepsin concentrations were measured by a commercially available chemiluminescent enzyme immunoassay (PATHFASTTM, Mitsubishi Chemical Europe GmbH, Düsseldorf, Germany). Reference limits were calculated using the non-parametric percentile method. Results: Overall, the reference limits for the presepsin were 55–184 pg/mL (90% confidence intervals, CI, were 45 to 58 and 161 to 214, respectively). There were no significant differences between males and females and the presepsin concentrations were not even particularly influenced by age. The upper reference limit for the presepsin is much lower than every cut-off limit so far proposed, both for sepsis and also for systemic inflammatory response syndrome. Conclusion: Specific decision levels are required to define the diagnostic and prognostic roles of presepsin in different settings of inflammatory and infectious diseases. Reference values can help to distinguish and quickly rule out healthy subjects or patients with other pathologie

analytical assessment of the new roche cobas t 711 fully automated coagulation analyzer

AbstractThis study aimed to provide a preliminary evaluation of the analytical performance of the new Roche cobas t 711 fully automated coagulation analyzer, which uses both liquid and lyophilized reagent cassettes. The analytical assessment included analysis of imprecision and linearity of prothrombin time (PT), activated partial thromboplastin time (APTT), and fibrinogen on cobas t 711 analyzer. Test results of 120 routine plasma samples were also compared with those obtained using two other coagulation analyzers (Instrumentation Laboratory ACL TOP 700 and Stago STA-R MAX). The accuracy, imprecision, and comparability of manual and automatic lyophilized material resuspension were also evaluated using 200 routine plasma samples. Overall, automatic resuspension was found to be more precise than, and equally accurate as, manual reconstitution, with coefficient of variations (CV%) three- to sixfold lower compared with manual reconstitution. The analytical imprecision was found to be excellent, as attested by total CV% of 0.7% for PT, 1.7 to 1.8% for APTT, and 1.9 to 3.2% for fibrinogen. Linearity was excellent over a clinically significant range of PT, APTT, and fibrinogen values, displaying correlation coefficients comprised between 0.994 and 0.999. Methods comparison studies revealed that results of PT, APTT, and fibrinogen on cobas t 711 are globally aligned with those obtained using identical plasma samples on IL ACL TOP 700 and Stago STA-R MAX, displaying correlation coefficients of 0.97 for PT, 0.81 and 0.88 for APTT, 0.90 and 0.94 for fibrinogen, respectively. In conclusion, the results of this preliminary evaluation demonstrate that PT, APTT, and fibrinogen on cobas t 711 coagulation analyzer displays excellent performance for routine use in clinical laboratories

Estimating Mean Pulmonary Wedge Pressure in Patients With Chronic Atrial Fibrillation From Transthoracic Doppler Indexes of Mitral and Pulmonary Venous Flow Velocity

AbstractObjectives. We sought to obtain a noninvasive estimation of mean pulmonary wedge pressure (MPWP) in patients with chronic atrial fibrillation (AF).Background. It has previously been demonstrated that MPWP can be reliably estimated from Doppler indexes of mitral and pulmonary venous flow (PVF) in patients with sinus rhythm. Doppler estimation of MPWP has not been validated in patients with AF.Methods. MPWP was correlated with variables of mitral and pulmonary venous flow velocity as assessed by Doppler transthoracic echocardiography in 35 consecutive patients. The derived algorithm was prospectively tested in 23 additional patients.Results. In all patients the mitral flow pattern showed only a diastolic forward component. A significant but relatively weak correlation (r = −0.50) was observed between MPWP and mitral deceleration time. In 12 (34%) of 35 patients, the pulmonary vein flow tracing demonstrated only a diastolic forward component; a diastolic and late systolic forward flow was noted in the remaining 23 patients (66%). A strong negative correlation was observed between MPWP and the normalized duration of the diastolic flow (r = −0.80) and its initial deceleration slope time (r = −0.91). Deceleration time >220 ms predicted MPWP ≤12 mm Hg with 100% sensitivity and 100% specificity. When estimating MPWP by using the equation MPWP= −94.261 PVF deceleration time− 9.831 Interval QRS to onset of diastolic PVF− 16.337 Duration of PVF+ 44.261, the measured and predicted MPWP closely agreed with a mean difference of −0.85 mm Hg. The 95% confidence limits were 4.8 and −6.1 mm Hg.Conclusions. In patients with chronic AF, MPWP can be estimated from transthoracic Doppler study of PVF velocity signals.(J Am Coll Cardiol 1997;30:19–26

MULTICENTER COMPARISON OF FOUR CONTEMPORARY SENSITIVE TROPONIN IMMUNOASSAYS MULTICENTRI^NO PORE\ENJE ^ETIRI SAVREMENA IMUNOESEJA OSETLJIVA NA TROPONIN

Summary Background: The IFCC Task Force on Clinical Applications of Cardiac Biomarkers currently recommends evaluation of all troponin immunoassays within the same population to compare their performance. Hence, we planned a multicenter study to compare the four most widespread contemporary sensitive troponin I (TnI) methods. Methods: Seventy-six serum samples were centrifuged, separated and divided in 5 aliquots. The first aliquot was used for clinical measurement, whereas the rest were shipped to participating laboratories, where they were simultaneously thawed. High-sensitivity troponin T (HS-TnT) was measured on a Roche Cobas, whereas TnI was assessed with the Ortho Vitros cTnI, Beckman Coulter DXI 800 AccuTnI, Siemens Vista cTnI and Abbott Architect STAT cTnI. Results: A substantial bias was found between TnI and HSTnT values. Although the correlation was acceptable and comprised between 0.86-0.89, the agreement of diagnostic values was poor, with the kappa statistic always lower than 0.50. Although the direct comparison between the four contemporary sensitive TnI immunoassays generated more favourable results, with Pearson's correlations greater than 0.970 and the kappa statistic equal to or higher than 0.59

Heart-Kidney Biomarkers in Patients Undergoing Cardiac Stress Testing

We examined association of inducible myocardial perfusion defects with cardiorenal biomarkers, and of diminished left ventricular ejection fraction (LVEF) with kidney injury marker plasma neutrophil gelatinase-associated lipocalin (NGAL). Patients undergoing nuclear myocardial perfusion stress imaging were divided into 2 groups. Biomarkers were analyzed pre- and poststress testing. Compared to the patients in the low ischemia group (n = 16), the patients in the high ischemia group (n = 18) demonstrated a significantly greater rise in cardiac biomarkers plasma BNP, NT-proBNP and cTnI. Subjects were also categorized based on pre- or poststress test detectable plasma NGAL. With stress, the group with no detectable NGAL had a segmental defect score 4.2 compared to 8.2 (P = .06) in the detectable NGAL group, and 0.9 vs. 3.8 (P = .03) at rest. BNP rose with stress to a greater degree in patients with detectable NGAL (10.2 vs. 3.5 pg/mL, P = .03). LVEF at rest and with stress was significantly lower in the detectable NGAL group; 55.8 versus 65.0 (P = .03) and 55.1 vs. 63.8 (P = .04), respectively. Myocardial perfusion defects associate with biomarkers of cardiac stress, and detectable plasma NGAL with significantly lower LVEF, suggesting a specific heart-kidney link

Academy of Emergency Medicine and Care-Society of Clinical Biochemistry and Clinical Molecular Biology consensus recommendations for clinical use of sepsis biomarkers in the emergency department.

Increasing evidence is emerging that the measurement of circulating biomarkers may be clinically useful for diagnosing and monitoring sepsis. Eight members of AcEMC (Academy of Emergency Medicine and Care) and eight members of SIBioC (Italian Society of Clinical Biochemistry and Laboratory Medicine) were identified by the two scientific societies for producing a consensus document aimed to define practical recommendations about the use of biomarkers for diagnosing of sepsis and managing antibiotic therapy in the emergency department (ED). The cumulative opinions allowed defining three grade A recommendations (i.e., highly recommended indications), entailing ordering modality (biomarkers always available on prescription), practical use (results should be interpreted according to clinical information) and test ordering defined according to biomarker kinetics. Additional grade B recommendations (i.e., potentially valuable indications) entailed general agreement that biomarkers assessment may be of clinical value in the diagnostic approach of ED patients with suspected sepsis, suggestion for combined assessment of procalcitonin (PCT) and Creactive protein (CRP), free availability of the selected biomarker(s) on prescription, adoption of diagnostic threshold prioritizing high negative predictive value, preference for more analytically sensitive techniques, along with potential clinical usefulness of measuring PCT for monitoring antibiotic treatment, with serial testing defined according to biomarker kinetics. PCT and CRP were the two biomarkers that received the largest consensus as sepsis biomarkers (grade B recommendation), and a grade B recommendation was also reached for routine assessment of blood lactate. The assessment of biomarkers other than PCT and CRP was discouraged, with exception of presepsin for which substantial uncertainty in favor or against remained

Laboratory testing in the emergency department: an Italian Society of Clinical Biochemistry and Clinical Molecular Biology (SIBioC) and Academy of Emergency Medicine and Care (AcEMC) consensus report

The mainstay of patient-oriented laboratory testing in emergency settings entails selecting number and type of tests according to valid criteria of appropriateness. Since the pattern of urgent tests requesting is variable across different institutions, we designed a joined survey between the Academy of Emergency Medicine and Care (AcEMC) and the Italian Society of Clinical Biochemistry and Clinical Molecular Biology (SIBioC) for reaching tentative consensus about the most informative diagnostic tests in emergency settings. A survey, containing the most commonly performed urgent laboratory tests and the relative clinical indications, was disseminated to eight relevant members of AcEMC and eight relevant members of SIBioC. All contributors were asked to provide numerical scores for the different laboratory parameters, where 1 indicated strongly recommended, 2 recommended in specific circumstances, and 3 strongly discouraged. The mean results of the survey were presented as the mean of responders' values, and the parameters were finally classified as strongly recommended (mean value, 1.0-1.5), somehow recommended (mean value, 1.5-2.0), discouraged (mean value, 2.0-2.5) and strongly discouraged (mean value, 2.5-3.0). The results of the survey allowed defining a hierarchy of priority, wherein 24 tests were strongly recommended. The use of 5 common tests was instead strongly discouraged. For 16 additional parameters in the list, the consensus ranged between somehow recommended and discouraged. We hope that results presented in this joint AcEMC-SIBioC consensus document may help harmonizing panel of tests and requesting patters in emergency setting, at least at a national level

Blood venous sample collection: Recommendations overview and a checklist to improve quality

The extra-analytical phases of the total testing process have substantial impact on managed care, as well as an inherent high risk of vulnerability to errors which is often greater than that of the analytical phase. The collection of biological samples is a crucial preanalytical activity. Problems or errors occurring shortly before, or soon after, this preanalytical step may impair sample quality and characteristics, or else modify the final results of testing. The standardization of fasting requirements, rest, patient position and psychological state of the patient are therefore crucial for mitigating the impact of preanalytical variability. Moreover, the quality of materials used for collecting specimens, along with their compatibility, can guarantee sample quality and persistence of chemical and physical characteristics of the analytes over time, so safeguarding the reliability of testing. Appropriate techniques and sampling procedures are effective to prevent problems such as hemolysis, undue clotting in the blood tube, draw of insufficient sample volume and modification of analyte concentration. An accurate identification of both patient and blood samples is a key priority as for other healthcare activities. Good laboratory practice and appropriate training of operators, by specifically targeting collection of biological samples, blood in particular, may greatly improve this issue, thus lowering the risk of errors and their adverse clinical consequences. The implementation of a simple and rapid check-list, including verification of blood collection devices, patient preparation and sampling techniques, was found to be effective for enhancing sample quality and reducing some preanalytical errors associated with these procedures. The use of this tool, along with implementation of objective and standardized systems for detecting non-conformities related to unsuitable samples, can be helpful for standardizing preanalytical activities and improving the quality of laboratory diagnostics, ultimately helping to reaffirm a "preanalytical" culture founded on knowledge and real risk perception

A survey on sample matrix and preanalytical management in clinical laboratories.

The vast majority of biochemistry tests is traditionally performed using either serum or heparinized plasma. Since little information is available on organization of clinical chemistry areas and type of biological samples used for this type of testing, the SIBioC Study Group on Extra-analytical variability planned a survey to be delivered to the members of the society. The questionnaire, consisting of 10 questions, was delivered by two newsletters and published on the SIBioC website for one month. Overall, 229 replies were collected from ~3000 society members. The most relevant aspect emerged from the survey was that serum not only was the most common biological matrix used for clinical chemistry tests (82% of responders), but it was also regarded as the ideal biological matrix (76% of responders). In 80% of cases, clinical chemistry testing was performed using blood collected in tubes containing a separator. Unlike ordinary testing, urgent analyses were performed using serum only in 58% of cases. The use of blood tubes with separator was also more frequent for urgent chemistry testing (64% of responders). A physical integration between clinical chemistry instruments was reported in approximately half of cases, whereas integration with preanalytical modules was reported to be slightly lower (45% of responders). The availability to change the biological matrix by the majority of responders demonstrates a substantial awareness that a major degree of harmonization should be pursued in the preanalytical phase