Biomedical subjects
Publications and source records attributed to J E Logan.
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The purpose of this document is to provide general considerations for the selection and evaluation of clinical chemistry kits in laboratories with limited resources. Separate documents have been developed to provide guidance on experimental procedure, the statistical treatment and interpretation of the data and criteria for acceptable performance of diagnostic kits designed to measure specific analytes.
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The purpose of the document is to state the policy of IFCC on the evaluation of clinical chemistry kit methods. Subsequent documents will provide specific guidance on experimental procedure, the interpretation of data and criteria for acceptable performance.
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A 20-point system is presented whereby commercially produced clinical chemistry procedures, i.e., in vitro diagnostic kits, may be assessed for adequacy of packaging, labelling and enclosed literature. Criteria are given for the selection of a reference method to use in the test method evaluation and the design of a patient comparison study using these two methods is described. The importance of standards and calibration materials as they relate to accuracy and specificity is discussed. A procedure for assessing accuracy by recovery studies is outlined. A method for the assessment of precision on a within-day and a day-to-day basis is described.
Recommendations are made concerning the editing of day-to-day reproducibility data for establishment of precision in the evaluation of a clinical chemistry method. The concept of diagnostic and equalized diagnostic indices is introduced together with formulae for their generation from the usual precision and accuracy data acquired in method evaluations. These indices allow direct comparison of data obtained from procedures for measuring enzyme activities which employ a variety of experimental conditions and units in their protocols. The equalized diagnostic index permits assessment of the suitability of the normal range assignment. Permissible limits of variation (PLV) and permissible limits of discrepancy (PLD) have been developed empirically from detailed examination of data from method evaluations and proficiency testing surveys in the published literature. The application of the diagnostic indices and the two permissible limits of criteria have been illustrated using data from the assessment of 19 kits measuring CPK activity. The inconsistency of the correlation coefficient in method comparisons is confirmed.
1. The factors influencing the measurement of creatine phosphokinase (CPK) activity in serum by coupled enzymatic methods were investigated to establish optimum conditions for this type of assay. Such a study was indicated following observations by the authors of poor performance of commerically produced reagent kits together with the failure of most of the established an well accepted methods to operate under true optimum zero order kinetics in the reaction phase state. 2. The factors invested were the effects of pH, substrate concentrations (creatine phosphate, glucose and NADP+), added auxiliary (hexokinase) and indicator (glucose-6-phosphate dehydrogenase) enzymes, dithiothreitol (DTT) as an activator and conditions of storage of substrate stability. DTT was found to be a suitable activator but not a reactivator of the reaction. The optimum concentrations of creatine phosphate, glucose and NADP+ were found to be 20.0, 20.0 and 2.0 mmol/litre, respectively. Optimum activieies of the enzymes, glucose-6-phosphate dehydrosenase and hexokinase were 1000 and 2000 units/litre, respectively. 3. The between-day precision of the method for measuring serum at pH 6.8 and 30 degrees C at three activity levels under the optimum conditions developed was excellent yielding coefficients of variation ranging from 2.0 to 2.7%.
1. A survey conducted among hospital laboratories has yielded data from 640 institutions concerning the use of diagnostic kits and reagents in Canada. 2. Kits designed to test for chemical constituents were most frequently used in hospitals of 51 to 600 bed capacity whereas the ones for enzymes were most extensively used in 201 to 700 bed-size institutions. Kits based on the CPB principles were generally used in hospitals of more than 200 beds whereas those based on RIA were only in frequent use where the bed capacity was 351 or more. 3. The following tests were most often performed by kits: aminotransferases, amylase, urea, LDH, phosphatases, glucose, CPK, bilirubin, calcium, uric acid, T-4, T-3, digoxin and vitamin B12. 4. The survey reflects a continuing and increasing usage of in vitro diagnostic kits and associated blood analyzer systems. It also indicates a significant adoption of assay kits which utilize RIA and CPB principles.
1. The evaluation of seven colorimetric and twelve kinetic or ultra-violet (UV) creatine phosphokinase (CPK) kit methods for their reliability as a diagnostic tool in clinical laboratories has revealed that over 35% of such commercial products readily available in Canada do not yield reliable results. 2. Six out of seven colorimetric kits failed to meet the criteria of minimum reliability as did one of the twelve UV kinetic kits.
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