Giampaolo Cattozzo

Myoglobin and creatine kinase isoenzyme MB mass assays: intermethod behaviour of patient sera and commercially available control materials.

The low biological variation of myoglobin and creatine kinase isoenzyme MB mass (CK-MBm) requires accurate measurements. In the standardization process, in order to effectively measure and correct intermethod variability, the intermethod behaviour of control materials must be the same of patient sera, i.e. they must be commutable. In this work we checked the commutability of some commercially available control materials in pairs of methods for myoglobin and CK-MBm measurements; we assessed the impact of commutable and non-commutable control materials when used for equalizing patient sera results by two different methods and discussed the problems related to external quality assessment schemes. Myoglobin and CK-MBm were measured in sets of 49 and 56 patient sera and in 13 commercially available control materials with two automatic analytical systems. The non-commutability rate was 8.3% for myoglobin and 23.1% for CK-MBm. Recalculation of serum samples results with a control material as calibrator lowered or increased the bias originally present according to whether the material itself was commutable or not. We conclude that also for myoglobin and CK-MBm assays it is necessary to check the commutability of materials to be used in external quality assessment schemes, or to normalize patient results by different methods.

Commutable Calibrator with Value Assigned by the IFCC Reference Procedure to Harmonize Serum Lactate Dehydrogenase Activity Results Measured by 2 Different Methods

BACKGROUND The availability of commutable calibrator materials may ease considerably the task of harmonizing assay results and ensuring their traceability to reference procedures. We sought to verify the commutability of potential calibrator materials and evaluate their effectiveness in harmonizing LDH results by 2 measurement methods. METHODS We measured LDH in 109 serum samples and 31 materials, including frozen serum pools (with either normal or abnormal isoenzyme patterns), commercial stabilized materials, and the ERM-AD453/IFCC reference material. We assayed LDH activity with the IFCC reference procedure and with 2 commercial methods, 1 using the lactate-to-pyruvate (LP) reaction, and the other the pyruvate-to-lactate (PL) reaction. We selected a commutable material, with LDH value assigned by the reference procedure, as a calibrator for recalculating the results for patient sera by both LP and PL, thereby making them traceable to the IFCC reference procedure. RESULTS Original values for patient sera (n = 109) by the 2 commercial methods showed a mean (SD) PL/LP ratio of 1.97 (0.03); this ratio changed to 1.06 (0.02) after recalculation of results. Linear regression of PL vs LP recalibrated values gave y = 1.108x - 9.7. At the clinically important concentration of 250 U/L (upper reference limit), the systematic difference between methods was 6.8%, which met our proposed quality specifications for inaccuracy and total error. CONCLUSIONS By properly selecting the calibrator, the results of serum LDH measurement by 2 different methods may be harmonized and made traceable to the selected highest (reference) metrological level.

Intermethod variation in serum carcinoembryonic antigen (CEA) measurement. fresh serum pools and control materials compared.

Abstract This study was undertaken to evaluate the feasibility of using commercial control materials in a regional external quality assessment scheme (EQAS) for serum carcinoembryonic antigen (CEA) measurement. We have assessed the commutability of 12 commercial control materials using five automated immunochemical systems. We compared the intermethod behavior of the materials with that of 12–14 patient serum pools. In a total of 48 comparisons (12 materials × 4 pairs of analytical systems), seven instances of noncommutability were apparent, as shown by normalized residuals falling outside the ±3 interval. The use of non-commutable materials generates two negative effects. In EQAS, the interlaboratory variation recorded is not representative of the variation expected in the assay of patient sera; in interlaboratory harmonization programs, recalibration with non-commutable materials increases, instead of decreasing, the interlaboratory variation. Both these effects were shown to occur in CEA measurement with the tested materials and systems. The materials planned to be used in our EQAS turned out to be commutable: this gave us the guarantee of measuring realistic interlaboratory variation values, although the check for commutability should be extended to all the analytical systems used by the participants in the scheme.

Evaluation of the analytical performance of the Beckman Coulter AU680 automated analytical system based on quality specifications for allowable performance derived from biological variation.

The Beckman Coulter AU680 (Beckman Coulter, Cassina De’ Pecchi, Italy) is a new analytical system, consolidating assays of various analytes. This random-access, fully automated, analyzer offers an on-board capacity of 60 photometric and three ion-selective electrode (ISE) different tests in parallel; its throughput is 800 photometric tests/hour and up to 1200 tests/hour with the ISE module. The AU680 system represents an upgrade of the AU640 system (Olympus Italia, Segrate, Italy), differing mainly by its (i) capacity to use reduced reagent and sample volumes, (ii) possibility to perform analytical methods requiring up to three reagents and (iii) priority lane performing re-runs quickly. This study was aimed to evaluate the AU680 system for precision and correlation in comparison with the AU640 for some routine assays. Furthermore, the IFCC-traceable claimed 3-part-reagent methods for alanine aminotransferase (ALT) and aspartate aminotransferase (AST), dealing a solution of pyridoxal-59-phosphate (P5P) as a separate reagent directly in the reaction cuvette, were compared to the relevant 2-partreagent IFCC methods. On the whole, 29 analytical methods for 21 assays were evaluated, including zero and first order rate reaction, end point, immunoturbidimetry and ISE methods. Adequacy of analytical performance to clinical employment was assessed with reference to quality specifications derived from biological variation (1–3).

Intermethod Variability of Sodium and Potassium Results: Patients Sera and Commercially Available Control Sera

Sodium and potassium were measured in sets of 102 to 107 patients sera, and in 31 commercially available control sera. The results from four routine analytical methods/systems (indirect potentiometry: two; direct potentiometry and enzymatic assay: one each) were compared with those from a flame photometry-based reference method. In the assay of patient sera, substantial agreement was observed in some comparisons, clinically relevant bias in others. The inter-assay changes observed for the control sera differed significantly from those shown by the patients sera (i.e. commercial control sera were non-commutable) in about 12% of the comparisons, as a whole. Recalculation of serum sample results with a single control serum as calibrator lowered or increased the bias originally present according to whether the serum itself was commutable or not. Moreover, the inter-method variability in the assay of commercial control sera was lower with commutable sera, higher with non-commutable sera. With the exception of liquid sera stabilized with ethylene glycol, there was no evident link between any specific characteristic of the commercial control sera (matrix and physical state) and their degree of commutability.

Normalizing intermethod free triiodothyronine patient results: need for commutable materials.

Abstract The aim of this work was to check the suitability of control materials to normalize intermethod results for the measurement of free triiodothyronine in patient sera. In the main experiment, 108 patient sera and 11 commercially available control materials were assayed by a pair of methods. In a confirmatory experiment, two of the control materials and 142 patient sera were assayed with an alternative pair of methods. In the main experiment, the intermethod variability of 6/11 control materials differed significantly from that of patient sera (i. e. control materials were non-commutable). Recalculation of patient results using control materials as calibrators lowered the intermethod difference only if commutable materials were used. The confirmatory experiment demonstrated that the pattern of commutability changed if a different pair of methods was used. We conclude that in the case of free triiodothyronine the commutability of control materials should be tested if they are to be used to normalize patient results obtained by different methods.

Reference values for alanine aminotransferase, α-amylase, aspartate aminotransferase, γ-glutamyltransferase and lactate dehydrogenase measured according to the IFCC standardization during uncomplicated pregnancy

Giampaolo Cattozzo*, Alessandra Calonaci, Chiara Albeni, Elena Guerra, Maria Franzini, Fabio Ghezzi and Ferruccio Ceriotti, on behalf of the Enzyme Working Group of the Italian Society of Clinical Biochemistry and Clinical Molecular Biology (SIBioC-Laboratory Medicine) Reference values for alanine aminotransferase, α-amylase, aspartate aminotransferase, γ-glutamyltransferase and lactate dehydrogenase measured according to the IFCC standardization during uncomplicated pregnancy

Serum cardiac troponin I after conventional and minimal invasive coronary artery bypass surgery

Abstract We evaluated myocardial release of cardiac troponin I (cTnI) in patients treated with conventional coronary artery bypass grafting (CABG), which employs extra-corporeal circulation, and different kinds of minimal invasive coronary artery bypass grafting (MICABG), a surgical technique where the operation is performed without extra-corporeal circulation. Furthermore, we evaluated the usefulness of serum cTnI measurement to detect perioperative myocardial infarction (PMI) after coronary artery bypass surgery. Thirty-one patients were included: sixteen underwent CABG, fifteen underwent different MICABG and five patients had PMI. Blood specimens for cTnI measurements were collected up to 72 hours after opening the graft. Aortic cross-clamping time was a minor determinant of myocardial damage; on the other side, the trauma during surgery correlated with the number of involved arteries and with the manoeuvre employed to obtain heart dislocation, and appeared a more important determinant of myocardial damage. In patients with PMI, the cumulative release of cTnI was higher than in patients free from PMI; however, only after 24–72 hours we observed significant differences in serum cTnI values, because the increased perioperative values of cTnI complicated the interpretation of the myocardial status and a single cut-off could not be used to exclude PMI.