Assessing subsets of analytes in context of detecting laboratory errors.

Laboratory error detection is a hard task yet plays an important role in efficient care of the patients. Quality controls are inadequate in detecting pre-analytic errors and are not frequent enough. Hence population- and patient-based detectors are developed. However, it is not clear what set of analytes leads to the most efficient error detectors. Here, we use three different scoring functions that can be used in detecting errors, to rank a set of analytes in terms of their strength in distinguishing erroneous measurements. We also observe that using evaluations of larger subsets of analytes in our analysis does not necessarily lead to a more accurate error detector. In our data set obtained from renal kidney disease inpatients, calcium, potassium, and sodium, emerged as the top-3 indicators of an erroneous measurement. Using the joint likelihood of these three analytes, we obtain an estimated AUC of 0.73 in error detection.

Elevated plasma fibrinogen gamma' concentration is associated with myocardial infarction: effects of variation in fibrinogen genes and environmental factors.

BACKGROUND: Fibrinogen gamma', a fibrinogen gamma-chain variant generated via alternative mRNA processing, has been associated with susceptibility to thrombotic disease. OBJECTIVE: The present case-control study searched for potential determinants of the plasma fibrinogen gamma' concentration and examined the relationship between this variant and risk of myocardial infarction (MI). PATIENTS AND METHODS: The Stockholm Coronary Artery Risk Factor study, comprising 387 postinfarction patients and 387 healthy individuals, was employed. The fibrinogen gamma (FGG) 9340T > C [rs1049636], fibrinogen alpha (FGA) 2224G > A [rs2070011] and fibrinogen beta (FGB) 1038G > A [rs1800791] polymorphisms were determined. The plasma fibrinogen gamma' concentration was measured by enzyme-linked immunosorbent assay. The multifactor dimensionality reduction method was used for interaction analyses on risk of MI. RESULTS: The FGG 9340T > C and FGA 2224G > A polymorphisms, total plasma concentrations of fibrinogen, insulin and high-density lipoprotein, and gender appeared to be independent determinants of plasma fibrinogen gamma' concentration in patients, and the corresponding determinants in controls included FGG 9340T > C and FGA 2224G > A polymorphisms and plasma fibrinogen concentration. An elevated plasma fibrinogen gamma' concentration proved to be an independent predictor of MI [adjusted odds ratio (OR) (95% CI): 1.24 (1.01, 1.52)]. The plasma fibrinogen gamma' concentration was involved in a high-order interaction with total plasma fibrinogen and the FGG 9340T > C and FGA 2224G > A polymorphisms, associated with a further increased risk of MI [OR (95% CI): 3.22 (2.35, 4.39)]. CONCLUSIONS: Plasma fibrinogen gamma' concentration influences the risk of MI, and this relationship seems to be strengthened by the presence of an elevated total plasma fibrinogen concentration and the FGG 9340T and FGA 2224G alleles.

Monoclonal antibody DS6 detects a tumor-associated sialoglycotope expressed on human serous ovarian carcinomas.

A newly developed murine monoclonal antibody, DS6, immunohistochemically reacts with an antigen, CA6, that is expressed by human serous ovarian carcinomas but not by normal ovarian surface epithelium or mesothelium. CA6 has a limited distribution in normal adult tissues and is most characteristically detected in fallopian tube epithelium, inner urothelium and type 2 pneumocytes. Pre-treatment of tissue sections with either periodic acid or neuraminidase from Vibrio cholerae abolishes immunoreactivity with DS6, indicating that CA6 is a neuraminidase-sensitive and periodic acid-sensitive sialic acid glycoconjugate ("sialoglycotope"). SDS-PAGE of OVCAR5 cell lysates has revealed that the CA6 epitope is expressed on an 80 kDa non-disulfide-linked glycoprotein containing N-linked oligosaccharides. Two-dimensional non-equilibrium pH gradient gel electrophoresis indicates an isoelectric point of approximately 6.2 to 6.5. Comparison of the immunohistochemical distribution of CA6 in human serous ovarian adenocarcinomas has revealed similarities to that of CA125; however, distinct differences and some complementarity of antigen expression were revealed by double-label, 2-color immunohistochemical studies. The DS6-detected CA6 antigen appears to be distinct from other well-characterized tumor-associated antigens, including MUC1, CA125 and the histo-blood group-related antigens sLea, sLex and sTn.

Transient nature of interference effects from heterophile antibodies: examples of interference with cardiac marker measurements.

Two-site immunoassay methods have become the standard technique for measurement of a wide variety of drugs, hormones, and cell proteins. One limitation of these methods is their susceptibility to interference from heterophilic antibodies present in the sera of some patients. Human anti-murine antibodies represent a common heterophile antibody that can bind to mouse immunoglobulin and as well as to immunoglobulin from other species. While the mechanism of human anti-murine antibody interference has been well characterized, the time course over which this interference occurs and the susceptibility of different immunoassay procedures to human anti-murine antibody interference from patients with human anti-murine antibody have not been as well described. We report on the time course of interference in assays for cardiac markers for two patients with human anti-murine antibodies. We measured creatine kinase MB isoenzyme (CKMB) and troponins I and T using three different vendors' immunoassay procedures. Our results demonstrate that assay interference due to human anti-murine antibody interference is a transient phenomenon. In one of our patients, human anti-murine antibody interference appeared suddenly, peaked approximately 9 days following its appearance, and gradually resolved over the next 3 weeks. In addition, we found that immunoassay methods from different vendors can show highly variable interference effects when human anti-murine antibody-containing specimens are analyzed.

Multiple regression analysis of interference effects from a hemoglobin-based oxygen carrier solution.

The use of hemoglobin-based oxygen carrier solutions in patients requiring blood transfusion will necessitate that clinical laboratories have mechanisms in place to evaluate the potential interference effect of these substances on testing methods. Because these oxygen carrier solutions contain acellular hemoglobin, but do not contain many of the intracellular enzymes and ions present in erythrocytes, interference effects from blood substitutes may be quite different when compared to in vivo or in vitro lysis of erythrocytes. We evaluated the potential interference effect of Diaspirin Cross-linked Hemoglobin on 29 different clinical laboratory analytes. Various combinations of these analytes were tested using the Hitachi 747 and 911 systems, a Beckman CX3, an Abbott AxSym, a Bayer Immuno I, and a Dade ACA IV; a total of 60 analyte/instrument combinations. We used the method of multiple regression analysis to classify interferences as analyte-dependent, analyte-independent, or a combination of the first two types. The presence of clinically significant test interference was derived by using the criteria for maximum allowable error specified in the Clinical Laboratory Improvement Amendments of 1988. Using these criteria, we found significant interference from Diaspirin Cross-linked Hemoglobin with 13 of 29 analytes tested. Interference was noted with the Hitachi 747 and 911 methods for albumin, alkaline phosphatase, total and conjugated bilirubin, cholesterol, total carbon dioxide, iron, lactate dehydrogenase, magnesium, total protein, and triglyceride. In addition, Diaspirin Cross-linked Hemoglobin interfered with measurement of L-lactate using the ACA IV and minor interference was noted with glucose measured using the Beckman CX3. Data from the interference studies was graphically displayed in the form of interference plots. These plots show the maximum allowable test error, due to Diaspirin Cross-linked Hemoglobin, as a function of analyte and interferent concentrations. Evaluation of the potential interference effect of hemoglobin-based oxygen carrier solutions with use of multiple regression analysis and graphical display of the resultant data in the form of interference plots allows for more reliable reporting of test results from specimens containing these products.

Statistical techniques for evaluating the diagnostic utility of laboratory tests.

Clinical laboratory data is used to help classify patients into diagnostic disease categories so that appropriate therapy may be implemented and prognosis estimated. Unfortunately, the process of correctly classifying patients with respect to disease status is often difficult. Patients may have several concurrent disease processes and the clinical signs and symptoms of many diseases lack specificity. In addition, results of laboratory tests and other diagnostic procedures from healthy and diseased individuals often overlap. Finally, advances in computer technology and laboratory automation have resulted in an extraordinary increase in the amount of information produced by the clinical laboratory; information which must be correctly evaluated and acted upon so that appropriate treatment and additional testing, if necessary, can be implemented. Clinical informatics refers to a broad array of statistical methods used for the evaluation and management of diagnostic information necessary for appropriate patient care. Within the realm of clinical chemistry, clinical informatics may be used to indicate the acquisition, evaluation, representation and interpretation of clinical chemistry data. This review discusses some of the techniques that should be used for the evaluation of the diagnostic utility of clinical laboratory data. The major topics to be covered include probabilistic approaches to data evaluation, and information theory. The latter topic will be discussed in some detail because it introduces important concepts useful in providing for cost-effective, quality patient care. In addition, an example illustrating how the informational value of diagnostic tests can be determined is shown.

Simplified interpretative format for assessing test interference: studies with hemoglobin-based oxygen carrier solutions.

Substances such as hemoglobin that interfere with analytical processes are recognized as a frequent source of error in laboratory medicine. Standard guidelines for assessment of test interferences assume that interference effects are not related to the concentration of the analyte being measured. However, previous investigations have demonstrated that interference effects can be markedly different, depending on the concentrations of interferent and analyte within the specimen. An experimental protocol for investigating these different types of interference effects has been developed. This protocol utilizes an orthogonally arranged matrix with progressively increasing concentrations of analyte and interferent. Evaluation of the measured analyte concentrations in specimens within the matrix using multiple regression analysis allows the magnitude, direction, and significance of each type of interference to be determined. Unfortunately, implementation of the interference data derived from the multiple regression analysis for judging the clinical acceptability of test results when an interferent is present is difficult. We describe a two-dimensional graphical format for evaluating the clinical acceptability of test results, based on criteria established under the Clinical Laboratory Improvement Amendments of 1988, in specimens containing hemoglobin-based oxygen carrier solutions.

Topical morphine in a canine model: a pilot study.

OBJECTIVE: To determine if topical morphine can enter the synovial cavity and the effect of ultrasound on this process. DESIGN: A randomized control trial to investigate which body fluids morphine enters after topical application. SETTING: A university animal laboratory. SUBJECTS: Ten mongrel dogs raised by the Comparative Medicine Department. All animals were certified to be free of disease, all had received standard scheduled immunizations, and none had been used for any other research. INTERVENTION: Topical morphine and ultrasound or topical morphine and sham ultrasound was applied to the knees of the dogs. Samples were obtained afterward from synovial fluid, serum, and urine, and were analyzed for the presence of morphine. MAIN OUTCOME MEASURES: Blood samples were collected every 60 minutes for 240 minutes, urine samples were collected at 120 minutes and 240 minutes, and synovial joint fluid was collected at 120 minutes and 240 minutes. The process of collection and analysis was the same for dogs treated with topical morphine and ultrasound and those treated with topical morphine and sham ultrasound. Fisher's exact test was used to test for an association between the use of ultrasound and the presence of morphine in the synovial fluid, serum, or urine. Two-sample t tests were used to test for group differences in mean body weight. RESULTS: All samples (synovial fluid, serum, and urine) were negative at time zero. All of the subsequent serum samples were negative for morphine. Two or three of the dogs in each group of five (ultrasound or sham ultrasound) had positive urine and synovial fluid samples at 120 and 240 minutes. Ultrasound did not affect the results. Body weight of the dogs influenced the results, with lighter animals having a significantly larger percentage (p=.03) of synovial fluid samples positive for morphine. CONCLUSION: Ultrasound did not affect the absorption of topical morphine in this canine model. Body weight may have influenced the results. Dogs that tested positive for morphine in synovial fluid had a lower mean body weight than dogs that did not test positive (p=.03).

Enzymatic markers of gallstone-induced pancreatitis identified by ROC curve analysis, discriminant analysis, logistic regression, likelihood ratios, and information theory.

We investigated the diagnostic utility of frequent serial determinations of aspartate aminotransferase, alanine aminotransferase (ALT), lipase, amylase, and the lipase/amylase (L/A) ratio for distinguishing patients with acute pancreatitis due to biliary obstruction from those with acute pancreatitis due to other pathogenesis. Analyzed were enzyme activities obtained at admission and peak enzyme activities identified retrospectively from serial measurements in 53 patients with acute pancreatitis due to various causes. We evaluated the data with multiple statistical tools. Discriminant analysis and logistic regression revealed the diagnostic significance of ALT at initial and peak values, and the maximum information provided by peak ALT was confirmed by both logistic regression and stratum-specific likelihood ratios. Stratum-specific likelihood ratios showed peak ALT > 150 U/L was highly diagnostic of biliary pancreatitis. The L/A ratio, either at admission or at peak, was the only other significant variable for identifying patients with acute pancreatitis due to biliary obstruction. A multivariate logistic discriminant function including ALT and the L/A ratio significantly discriminated biliary acute pancreatitis from pancreatitis due to other causes. Evaluation of initial and peak enzyme data by information theory revealed that the optimal test depended on disease prevalence. Initial ALT activities were the test of choice for identifying biliary pancreatitis, up to a disease prevalence of approximately 0.75. At disease prevalence > 0.75, the initial L/A ratio provided the greatest amount of diagnostic information.

Identification and quantitation of drugs of abuse in urine using the generalized rank annihilation method of curve resolution.

A rapid analytical method which is of practical use for the identification and quantitation of drugs of abuse in urine using HPLC with a diode-array detection is described. Because the method utilizes mathematical resolution of partially resolved peaks, greatly simplified sample preparation procedures and very short run times can be used. The generalized rank annihilation method (GRAM) is used to eliminate response due to unknown background peaks and separate partially resolved peaks. An optimized gradient elution program was found for which morphine, phenylpropanolamine, ephedrine, benzoylecgonine, lidocaine, cocaine, diphenhydramine, nortriptyline, norpropoxyphene, nordiazepam, codeine, D-amphetamine, meperidine, and amitriptyline elute from the HPLC column in less than 8.5 min. A commercially available system for HPLC analysis of drugs of abuse is currently available, however, the commercially available system takes 21 min to complete its analysis. Two modified sample pre-treatment methods were also developed to simplify sample treatment procedures substantially. In this paper, The GRAM technique is shown to be extremely powerful in identifying drugs of abuse from large overlapping peaks.

Diagnostic accuracy of pancreatic enzymes evaluated by use of multivariate data analysis.

We analyzed pancreatic enzyme data from 508 patients with suspected pancreatitis by neural network analysis, by an Expert multirule generation protocol, and by receiver-operator characteristic (ROC) curve analysis of a single test result. Neural network analysis showed that use of lipase provided the best means for diagnosing pancreatitis. Diagnostic accuracies achieved by using amylase only, lipase only, and amylase and lipase in combination were 76%, 82%, and 84%, respectively. Use of the Expert rule generation protocol provided a diagnostic accuracy of 92% when rules for single and multiple samplings were combined. ROC curve analysis for initial enzyme activities showed the maximal diagnostic accuracy to be 82% and 85% for amylase and lipase, respectively; use of peak enzyme activities yielded accuracies of 81% and 88%, respectively. The evaluation of laboratory test data should include analysis of the diagnostic accuracy of laboratory tests by multivariate techniques such as neural network analysis or an Expert systems approach. Multivariate analysis should allow for a more realistic assessment of the diagnosis accuracy of laboratory tests because all the available data are included in the evaluation.

Laboratory error undetectable by customary quality control/quality assurance monitors.

The preanalytical, analytical, and postanalytical rates of laboratory error have not been studied extensively. We evaluated the preanalytical, analytical, and postanalytical components of laboratory error in 438 consecutive samples submitted to a clinical chemistry laboratory for measurement of creatinine concentrations in plasma. We performed red blood cell antigen determinations to establish patient-sample identity, repeated analysis of creatinine in duplicate to detect analytical error, and tracking of patient specimens from receipt by the laboratory to entry of the laboratory result in the patient's information system record. We found a total error rate of 9.36%. A breakdown of the total error rate into its preanalytical, analytical, and postanalytical components revealed error rates of 0.00%, 8.90%, and 0.46%, respectively. These results suggest that preanalytical and postanalytical error, which are not usually detectable by common quality control strategies, are not major sources of laboratory error. Further work is needed to reduce the unacceptably high rate of analytical errors.

Evaluation of a spectrophotometric method for measurement of activity of diamine oxidase in newborn infants.

Diamine oxidase (DAO) is an enzyme synthesized primarily in the gastrointestinal mucosal cells. Serum levels of DAO have been used as an indicator of the integrity and/or functional mass of the intestinal mucosa. The enzyme is also produced by the placenta and is elevated in newborn serum. Previous radiometric methods for DAO used tritiated putrescine or cadaverine as substrate. A simple and rapid spectrophotometric procedure for DAO with use of histamine as substrate was developed, and this assay was utilized to evaluate the developmental pattern of activity of DAO in umbilical cord blood of newborn full-term and premature infants, in sequential samples from premature infants, and in samples from infants with necrotizing enterocolitis. The spectrophotometric assay was linear to 200 U per L and was also precise with total imprecision (CV) of 11.9 percent and 3.7 percent at DAO activities of 25.6 U per 1 and 126.1 U per L, respectively. Triglycerides above 275 mg per dL caused a significant reduction in measured activity of DAO; however, this effect could be eliminated by use of ultracentrifugation to remove lipemia. Plasma samples with heparin or ethylenediamine tetraacetic acid (EDTA) as anticoagulant were unsuitable for analysis since DAO activity showed a 24 percent and 32 percent decrease in activity at concentrations of 20 U per mL (heparin) and two mg per mL (EDTA), respectively. Serum samples are the specimen of choice. In infants it was found that the serum activity declined to adult levels by day 12 of life and that this decline is not affected by necrotizing arterocolitis.