Ruth Cano-Corres

Lack of commutability between a quality control material and plasma samples in a troponin I measurement system.

The concept of commutability expresses the closeness of the relationship between the results of different measurement procedures for a reference or control material and those obtained for patient samples. With regard to clinical laboratories, it is frequently assumed that the imprecision in a measurement system used for commercial control materials will be similar when the system is used for human samples. However, studies suggest that this assumption may be erroneous (1 – 4) . Therefore, estimating imprecision in the measurement of human samples may be necessary for calculating the real imprecision inherent in the measurement systems. This is particularly relevant to certain cases, such as troponin measurements. This is because there is an international consensus regarding the level of imprecision in the decision limit used to diagnose myocardial injury (CV ≤ 10 % ) (5) . The CV is usually calculated using commercial control materials, and the aim of clinical laboratory professionals is to keep the level of imprecision below this level. For this reason, any lack of commutability between the control/reference material and the clinical samples means that the control material can no longer be used, as it would not accurately refl ect the real imprecision of the procedure. Therefore, to address this, we studied the interchangeability of day-to-day imprecision of measurements of the commercial control material that we usually use in our laboratory, and of the measurements of pooled plasma samples. The plasma concentrations of troponin I were measured using a Dimension RxL analyser (Siemens Healthcare Diagnostics Products, Marburg, Germany) according to the manufacturer ’ s instructions. The day-to-day imprecision in this procedure were estimated simultaneously using control materials containing cardiac markers at different concentrations (Dade ® Cardiac TL; levels 1, 2 and 3, ref B5960-1, Siemens Healthcare Diagnostics Products, Marburg, Germany), and three plasma pools containing troponin I at concentrations close to those in the controls. Each of the control materials was previously aliquoted and refrigerated at 4 ° C, and each plasma pool was divided into 20 aliquots and stored at – 20 ° C. Troponin concentrations were measured daily over a period of 20 working days (one measurement for each of the control materials and one for the plasma pool). When the 20 measurements were complete, the corresponding variances and CVs, which represent day-today imprecision in the measurements, were estimated. The CVs are shown in Table 1 . An F-test (p set at < 0.05) was then used to determine the interchangeability of day-to-day imprecision in the measurement of the control materials and plasma pools. The data (shown in Table 1) confi rm that the variances were not interchangeable. This study shows the marked lack of commutability between a very well used commercial control material and plasma pools. The most relevant fi nding was that the imprecision estimated using the control materials was higher than that obtained for the plasma samples. A previous study reported similar fi ndings (3) , although the opposite situation is more common. Since it is required that the level of imprecision for troponin measurements at the decision limit must be less than or equal to 10 % (5) , clinical laboratory professionals are always aiming to decrease the CV obtained using control materials. A lack of commutability associated with higher imprecision of control materials generates problems due to over-controlling to maintain the inter-serial imprecision level below 10 % . This results in an unnecessary waste of control materials, reagents, and human resources without any extra benefi t in terms of more accurate patient results. In conclusion, it is important to know whether there is commutability between commercially available troponin control materials and human samples, at least until the in vitro diagnostics industry can produce control materials that have imprecision interchangeable with human samples, and can provide documental evidence that this is the case. Although this study focused on troponin I, commutability is essential for all measurements made in clinical laboratories.

Evaluation of biological fluid analysis using the sysmex XN automatic hematology analyzer

Hematological cytometers with a biological fluid module could potentially correct the limitations of the manual chamber method. This study evaluates the agreement between the manual technique and the Sysmex XN‐1000 analyzer for white blood cell (WBC) and red blood cell (RBC) counts, as well as for leukocyte differentiation in different types of fluids. This study also evaluates the advantages of incorporating the technique in routine laboratory work.

Proposed criteria for sorting examined properties in clinical laboratory reports

Abstract To date not much importance has been given to the sorting of examined properties (“tests”) in clinical laboratory reports. The present article contains a proposal about sorting the examined properties of clinical laboratory reports, in order to facilitate their interpretation to the requesting physicians. This proposal is mainly based on clinical and patho-physiological criteria. A set of groups of properties has been established according to the main clinical indications of each property. Some of these properties have several clinical indications and, consequently, have been included in more than one group. Some of these groups have been associated to other groups, so that the properties conforming them will always appear consecutively, since they are patho-physiologically related. Finally, an association between each group with the different medical specialities or areas of knowledge has been made, according to the clinical indications of each property. The groups of properties proposed are in concordance with their main clinical indications and their patho-physiological relationship. This ordering system gives priority, first, to the alarm (critical) values and, second, to the medical speciality or knowledge area of the requesting physician. This proposal can help the requesting physician to see first of all the most relevant clinical laboratory information related to her/his patient.

Influence of 6 genetic variants on the efficacy of statins in patients with dyslipidemia

Patients with dyslipidemia are often treated with statins to reduce lipids and hence cardiovascular risk, but treatment response is variable, partly due to genetic factors.

Loss of retinol stability in patient samples.

Retinol plays an essential role in the visual process [1], growth, immune response and some studies also suggest an anti-inflammatory and anti-carcinogenic action [2]. Some malabsorption diseases like pancreatitis or cystic fibrosis can cause retinol deficiency [3], which causes anemia, xerophthalmia, and growth delay [4, 5]. However, high levels of retinol can potentially be toxic [6]. Thus, measurement of plasma retinol is essential in different pathologic situations. Retinol plasma reference values are defined by the following interval (0.3–1.0) mg/L. These values have been established in our laboratory from different recommendations [5]. In our laboratory, plasma concentrations of retinol and tocopherol are measured simultaneously by reversedphase liquid chromatography coupled with spectrophotometric detection. The sample preparation consists in protein precipitation and retinol/tocopherol extraction with ethanol and hexane. This extract is evaporated with nitrogen in a TurboVap LV evaporator at 40 °C, and then reconstituted with methanol. TurvoVap LV is a concentrator-evaporator which permits monitoring the evaporation process, keeping constant the gas flow and the temperature. The separation is performed with a SunFire® C8 (3.5 μm 4.6 × 75 mm) column using an isocratic mixture of 8% water and 92% methanol as the mobile phase, and a flow rate of 1 mL/min. Retinol acetate is used as internal standard. Retinol is detected at 325 nm and tocopherol at 295 nm. The injection volume is 20 μL and the total run time 14 min. The temperature of the samples in the chromatograph refrigeration chamber is 15 °C. Every working series includes one calibrator, two internal quality controls and at least 10 patient samples. It is known that retinol is light labile, so it must be stored under strict conditions [7]. Patient samples must be protected from the light and maintained frozen until their processing. We detected a loss of stability during sample dataset processing. In every series we injected the same sample, an internal quality control, from the same vial, at the beginning and the end of the series, and we realized that there were significant differences between the results. The whole processing time was about 4 h and the difference between the results of the repeated sample was over 12%, with the last replicate always being higher. To reject the existence of carry-over between samples we processed a water sample, extracted like a patient sample, in the middle of a sample series. The only compound detected in the water sample was the internal standard, so we concluded that there was no carry-over between samples. To verify and quantify the differences between results, we processed the same sample seven consecutive times. The average difference between correlative injections was 1.6% and the difference rose 12% between the first and the last one. This experiment was duplicated, obtaining similar results: 2.1% between consecutive injections and 13% between the first and the last one. We suspected that there could be evaporation of the sample which could concentrate the retinol. We processed a sample without tap in the middle of a normal series to check this hypothesis, and after 4 h of processing the vial was empty. We assumed that the loss of stability was due to evaporation, and it could be related to the evaporation temperature, refrigeration chamber temperature or the taps of the vials. The employed vials showed different resistance to the first and second injection, so this fact could cause differences in the chromatogram. We decided to divide the sample into two different vials to avoid the effect of the second injection on the tap. The next experiment consisted in reducing the temperature of the refrigerating chamber and/or the *Corresponding author: Ruth Cano-Corres, UDIAT CD, Corporació Sanitaria Parc Tauli, Parc Tauli s/n CP: 08208 Sabadell, Barcelona, Spain, Phone: +93 7458439 (26118), E-mail: ruthcanocorres@gmail.com; and Laboratory, Biochemistry, UDIAT CD, Corporació Sanitaria Parc Tauli, Sabadell, Barcelona, Spain Eugenio Berlanga-Escalera: Laboratory, Biochemistry, UDIAT CD, Corporació Sanitaria Parc Tauli, Sabadell, Barcelona, Spain