Evaluation of the accuracy of "ChE check mobile" in measurement of acetylcholinesterase in pesticide poisoning.

BACKGROUND: Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) are used in clinical management to confirm the diagnosis and indicate the severity of organophosphorus and carbamate poisoning. ChE check mobile is a new portable cholinesterase testing system developed in Germany. The study aims to evaluate the accuracy of ChE check mobile compared to the standard reference method and Test-mate ChE system. METHODS: Patients with organophosphorus and carbamate poisoning were recruited from two general hospitals in Sri Lanka between September 2013 and November 2014. The AChE was measured using the three methods. RESULTS: Blood samples were collected from 185 self-poisoned patients (170 organophosphorus and 15 carbamate) and 20 normal individuals. ChE check mobile correlated well with spectrophotometer readings (Pearson's correlation coefficient 0.87) but gave higher values (Mean bias for AChE: +6.55 (95% CI: -11 to 24) U/g Hb). A similar positive bias from Test-mate results was also observed. Applying a correction factor derived from the volunteer samples (dividing by 1.353) greatly improved agreement in pesticide poisoned patients. CONCLUSIONS: ChE check mobile system allowed for rapid determination of AChE activity but gave somewhat higher AChE compared to other methods. Applying a correction factor of 1.353 provide a good agreement to both reference and Test-mate ChE machine in this setting.

Validation of the quantitative point-of-care CareStart biosensor for assessment of G6PD activity in venous blood.

INTRODUCTION: Glucose-6-phosphate dehydrogenase (G6PD) deficiency is the most common enzymopathy in the human population affecting an estimated 8% of the world population, especially those living in areas of past and present malaria endemicity. Decreased G6PD enzymatic activity is associated with drug-induced hemolysis and increased risk of severe neonatal hyperbilirubinemia leading to brain damage. The G6PD gene is on the X chromosome therefore mutations cause enzymatic deficiency in hemizygote males and homozygote females while the majority of heterozygous females have an intermediate activity (between 30-80% of normal) with a large distribution into the range of deficiency and normality. Current G6PD qualitative tests are unable to diagnose G6PD intermediate activities which could hinder wide use of 8-aminoquinolines for Plasmodium vivax elimination. The aim of the study was to assess the diagnostic performances of the new Carestart G6PD quantitative biosensor. METHODS: A total of 150 samples of venous blood with G6PD deficient, intermediate and normal phenotypes were collected among healthy volunteers living along the north-western Thailand-Myanmar border. Samples were analyzed by complete blood count, by gold standard spectrophotometric assay using Trinity kits and by the latest model of Carestart G6PD biosensor which analyzes both G6PD and hemoglobin. RESULTS: Bland-Altman comparison of the CareStart normalized G6PD values to that of the gold standard assay showed a strong bias in values resulting in poor area under-the-curve values for both 30% and 80% thresholds. Performing a receiver operator curve identified threshold values for the CareStart product equivalent to the 30% and 80% gold standard values with good sensitivity and specificity values, 100% and 92% (for 30% G6PD activity) and 92% and 94% (for 80% activity) respectively. CONCLUSION: The Carestart G6PD biosensor represents a significant improvement for quantitative diagnosis of G6PD deficiency over previous versions. Further improvements and validation studies are required to assess its utility for informing radical cure decisions in malaria endemic settings.

Leukocyte esterase reagent strip as a bedside tool to detect peritonitis in patients undergoing acute peritoneal dialysis.

Peritonitis is a common and life-threatening complication of acute peritoneal dialysis (PD). Diagnosis requires the presence of clinical signs of peritonitis which are nonspecific and laboratory investigations [total leukocyte count (TLC), Gram-stain, and culture of PD effluent fluid] which are time-consuming and not available at the bedside. In this study, we evaluated the use of leukocyte esterase reagent strip (LERS) as a bedside test to diagnose peritonitis in patients undergoing acute PD. Patients who underwent acute PD were monitored for signs and symptoms of peritonitis. PD effluent fluid analysis included TLC, absolute neutrophil count, Gram-stain, and culture for the diagnosis of peritonitis. LERS (Multistix 10SG) was simultaneously dipped in PD effluent fluid and read at two minutes. Reading of + was considered as indicative of peritonitis. Twenty-one out of 166 (12.6%) patients undergoing acute PD developed peritonitis. LERS detected peritonitis in 20 patients. The sensitivity, specificity, positive predictive value, and negative predictive value (NPV) of LERS were 95.2%, 95.2%, 74.1%, and 99.3%, respectively. LERS has very high sensitivity and NPV and can be used as a rapid bedside tool to exclude peritonitis in patients undergoing acute PD.

Caso familiar com diagnóstico para doença de Fabry / Familiar case with diagnostics for Fabry disease

A doença de Fabry é uma enfermidade genética ligada ao cromossomoX e de caráter progressivo, causada pela deficiênciaparcial ou total da enzima alfa galactosidase A (?-Gal A). Habitualmenteo diagnóstico é tardio em função das complicaçõespatológicas provocadas pela deficiência da enzima. OBJETIVO:Neste estudo, descrevemos os aspectos clínicos de um caso familiaratravés do acompanhamento ao longo de 3 anos, duranteo tratamentopela reposição enzimática. MÉTODOS: O métodoadotado foi indutivo, relacionado ao estudo de caso familiarde pacientes com doença de Fabry. Quanto à natureza das informações,a pesquisafoi qualitativa, utilizando-se, quanto aoseu objetivo, à pesquisa exploratória. Com relação as fonte deinformação e procedimento de coleta, a pesquisa caracteriza-secomo sendo bibliográfica e documental. A amostra foi compostapor três pacientesque realizamacompanhamento quinzenalpara aplicação de terapia de reposição enzimática. O critério deinclusão para a pesquisa partiu do pressuposto de se considerarque a doença de Fabry é uma afecção rara e que a família estudadacontempla com riqueza manifestações clínicas, capazesde caracterizar a doença de Fabry. RESULTADOS: Os principaissintomas clínicos relatados pelos pacientes foram: crisede dor generalizada, fadiga, acroparestesia, febre, mialgia, dorabdominal, hipohidrose, intolerância ao frio, calor e ao exercíciofísico. Esses sintomas segundo os pacientes surgiram nainfância e foram amenizados após o uso da terapia de reposiçãoenzimática, propiciando uma melhor qualidade de vida para osmesmos. Também, se observou sinais específicos desta patologianos pacientes, como córnea verticillata e angioqueratoma. Atravésda genotipagem se verificou a semelhança da mutação entre os pacientes do estudo, demonstrando padrão típico de herançarecessiva ligada ao cromossomo X. CONCLUSÃO: Os pacientesdeste estudo apresentaram quadro clínico semelhante,sendoque a sintomatologia iniciou na infância. Córnea verticillata eangioqueratoma umbilical foram sinais encontrados nos pacientes do sexo masculino e são considerados manifestações clínicas frequentes desta patologia. A herança encontrada nesta amostra tem um padrão típico de herança recessiva ligada ao cromossomo X. Desta forma, apesar de ser uma afecção rara na população em geral, o diagnóstico precoce e a terapia de reposição enzimática permitem a evolução clínica favorável e a melhoria da qualidade de vida do paciente.(AU)

Fabry disease is a genetic disorder linked to the X chromosomeand progressive, caused by partial or total deficiency of alphagalactosidase A (?-Gal A). Usually the diagnosis is delayed dueto the pathological complications caused by deficiency of theenzyme. OBJECTIVE: In this study, we describe the clinicalaspects of a family case by monitoring for over three years,during the treatment by enzyme replacement. METHODS:The method adopted was inductive, related to the study of afamily case with patients with Fabry disease. About the nature ofthe information, the research was qualitative, using, as its goal,the exploratory research. Regarding the source of informationand collection procedure, the research is characterized asbibliographical and documentary. The sample was composed ofthree patients submitted to biweekly monitoring for applicationof enzyme replacement therapy. The inclusion criterion forthe research assumed to consider that Fabry disease is a raredisease and that the studied family contemplates with wealththe clinical manifestations, able to characterize the Fabrydisease. RESULTS: The main clinical symptoms related bypatients were: generalized pain crisis, fatigue, acroparesthesia,fever, myalgia, abdominal pain, hypohidrosis, intolerance tocold, heat and exercise. These symptoms according to patientsemerged in childhood and were alleviated after the use ofenzyme replacement therapy, providing a better quality of lifefor them. Also, we found specific signs of this disease in patients,as verticillata cornea and angiokeratoma. By genotyping, it wasfound the similarity of the mutation among patients in thestudy, showing typical pattern of recessive inheritance linkedto chromosome X. CONCLUSION: The patients in this study showed similar clinical condition, and the symptoms began inchildhood. Verticillata cornea and umbilical angiokeratomasigns were found in male patients and are considered commonclinical manifestations of this pathology. The heritage found inthis sample has a typical pattern of recessive inheritance linkedto chromosome X. Thus, despite being a rare disease in generalpopulation, early diagnosis and enzyme replacement therapyallow favorable clinical evolution and improved patient qualityof life.(AU)

Microfluidic enzymatic biosensing systems: A review.

Microfluidic biosensing systems with enzyme-based detection have been extensively studied in the last years owing to features such as high specificity, a broad range of analytes and a high degree of automation. This review gives an overview of the most important factors associated with these systems. In the first part, frequently used immobilization protocols such as physisorption and covalent bonding and detection techniques such as amperometry and fluorescence measurements are discussed with respect to effort, lifetime and measurement range. The Michaelis-Menten model describing the kinetics of enzymatic reactions, the role of redox mediators and the limitations of the linear measurement range of enzymatic sensors are introduced. Several possibilities of extending the linear measurement range in microfluidic systems such as diffusion-limiting membranes and the flow injection setup are presented. Regarding the integration of enzymes into microfluidic systems during the fabrication process, the constraints imposed by the biomolecules due to the limited usage of high temperatures and solvents are addressed. In the second part, the most common forms of enzyme integration into microfluidic systems, i.e. in channels and on electrodes, on microparticles, on paper and thread and as injected enzyme solutions, are reviewed, focusing on fabrication, applications and performance.

The Usefulness of a Novel Screening Kit for Colorectal Cancer Using the Immunochromatographic Fecal Tumor M2 Pyruvate Kinase Test.

BACKGROUND/AIMS: M2 pyruvate kinase (M2-PK) is an enzyme that is produced in undifferentiated and proliferating tissues. This study aims to evaluate the usefulness of the immunochromatographic M2 pyruvate kinase (iM2-PK) for the screening of colorectal cancer (CRC) and premalignant lesions. METHODS: Healthy volunteers and patients with colorectal neoplasia were enrolled in six academic hospitals in the capital province of Korea. The iM2-PK value was compared with the immunochromatographic fecal occult blood test (iFOBT) and fecal tumor M2-PK enzyme-linked immunosorbent assay (ELISA). RESULTS: A total of 323 subjects were enrolled. The sensitivity of iM2-PK for CRC was 92.8%, which was superior to iFOBT (47.5%, p<0.0001). For adenomatous lesions, the sensitivity of iM2-PK was 69.4%, which was also superior to iFOBT (12.1%, p<0.001). Compared with M2-PK ELISA, iM2-PK exhibited significantly enhanced sensitivity for CRC (97.5% vs 80.0%, p=0.0289). The sensitivity of iM2-PK was higher in advanced stages of CRC compared with cancers confined to the mucosa and submucosa (p<0.05). However, lymph node metastasis had no influence on the sensitivity of iM2-PK. CONCLUSIONS: The iM2-PK exhibited increased sensitivity for identifying CRC and adenomatous lesions compared with iFOBT. Given its rapid results and convenience, CRC screening using iM2-PK is promising.

The Usefulness of a Novel Screening Kit for Colorectal Cancer Using the Immunochromatographic Fecal Tumor M2 Pyruvate Kinase Test

BACKGROUND/AIMS: M2 pyruvate kinase (M2-PK) is an enzyme that is produced in undifferentiated and proliferating tissues. This study aims to evaluate the usefulness of the immunochromatographic M2 pyruvate kinase (iM2-PK) for the screening of colorectal cancer (CRC) and premalignant lesions. METHODS: Healthy volunteers and patients with colorectal neoplasia were enrolled in six academic hospitals in the capital province of Korea. The iM2-PK value was compared with the immunochromatographic fecal occult blood test (iFOBT) and fecal tumor M2-PK enzyme-linked immunosorbent assay (ELISA). RESULTS: A total of 323 subjects were enrolled. The sensitivity of iM2-PK for CRC was 92.8%, which was superior to iFOBT (47.5%, p<0.0001). For adenomatous lesions, the sensitivity of iM2-PK was 69.4%, which was also superior to iFOBT (12.1%, p<0.001). Compared with M2-PK ELISA, iM2-PK exhibited significantly enhanced sensitivity for CRC (97.5% vs 80.0%, p=0.0289). The sensitivity of iM2-PK was higher in advanced stages of CRC compared with cancers confined to the mucosa and submucosa (p<0.05). However, lymph node metastasis had no influence on the sensitivity of iM2-PK. CONCLUSIONS: The iM2-PK exhibited increased sensitivity for identifying CRC and adenomatous lesions compared with iFOBT. Given its rapid results and convenience, CRC screening using iM2-PK is promising.

Diagnosis of spontaneous bacterial peritonitis in children by reagent strips.

This study was aimed to evaluate the efficacy of dipstick tests (leukocyte esterase and nitrite) in diagnosis of spontaneous bacterial peritonitis (SBP) in cirrhotic patients. Forty six children with ascites hospitalized between 2009 and 2010 in Children Medical Center were enrolled in this study. Reagent strip assays for leukocyte esterase and nitrite were performed on ascetic fluid and the results were compared to manual cell counting and ascitic fluid culture. SBP was defined as having a polymorphonuclear ascites count of ≥ 250/mm3. Twenty children were female and twenty six were male with mean age of 3±3.9 years. The sensitivity specificity, positive and negative predictive values of the leukocyte esterase reagent strips were all 100%. The sensitivity, specificity, positive and negative predictive value of the nitrite reagent strip test were 100%, 97%, 90% and 100% respectively. Leukocyte esterase reagent strips may provide a rapid, bedside diagnostic test for the diagnosis of SBP.

Rapid diagnosis of spontaneous bacterial peritonitis using leukocyte esterase reagent strips in emergency department: uri-quick clini-10SG® vs. Multistix 10SG®.

BACKGROUND AND AIM: Bacterial peritonitis (SBP) is the most frequent infection in patients with cirrhosis causing significant mortality. Delay in SBP diagnosis is a serious problem. The aim of this study was to evaluate the diagnostic yield of Uri-Quick Clini-10SG® vs. Multistix 10SG® reagent strips in an Emergency Department. MATERIAL AND METHODS: A prospective study of consecutive patients with ascites and paracentesis attending to Emergency Department from March 2005 to February 2007 was made. SBP was defined by ≥ 250 neutrophiles /mm³. The ascites obtained at bedside was immediately tested in a dry test tube with both the Uri-Quick Clini 10SG® and MultistixSG10®. The Uri-Quick Clini 10SG® and Multistix SG10®. Strips were considered positive at grade ≥ 3 (≥ 125 leukocytes/mL). RESULTS: A total of 223 ascitic fluid samples were obtained. There were 49 episodes of SBP. Median age was 54 (range 18-87 year) years; 62.3% were female. The sensitivity, specificity, PPV, NPV, and 95% CI for Uri-Quick Clini 10SG® were 79.6 (64-87), 98.2 (94-99), 90.5 (78-96) and 93.9 (89-96), respectively. For MultistixSG10® the values were 77.5 (64-88), 97.7 (93-98), 90 (77.9-96.2), and 94 (89.4-96.6), respectively. CONCLUSION: The use of reagent strip is useful for SBP diagnosis in an emergency setting. The high PPV allow start antibiotic treatment. In areas without the resources to perform conventional ascites fluid analyses, these strips could be presently used.

Validity of the urinary trypsinogen-2 test in the diagnosis of acute pancreatitis.

OBJECTIVES: A simple urinary trypsinogen-2 test was evaluated for the diagnosis of acute pancreatitis. METHODS: This prospective multicenter study enrolled consecutive patients with acute abdominal pain who presented to the emergency department or who were hospitalized at 1 of 21 medical institutions in Japan. Patients were tested with urinary trypsinogen-2 dipstick test and a quantitative trypsinogen-2 assay, and these values were compared with serum amylase and lipase findings. RESULTS: A total of 412 patients were enrolled. The trypsinogen-2 dipstick test was positive in 107 of 156 patients with acute pancreatitis (sensitivity, 68.6%) and in 33 of 256 patients with nonpancreatic abdominal pain (specificity, 87.1%). The sensitivity for the diagnosis of pancreatitis caused by alcohol and gallstones by the dipstick test was 72.2% and 81.8%, respectively, which was much higher than those associated with amylase testing. There are several degrees of positivity within the urinary trypsinogen-2 dipstick test. Modification of the cutoff point such that positive (+) and most positive (++) results were interpreted as a positive result, the specificity and positive likelihood ratio increased to 92.2% and 7.63, respectively. CONCLUSIONS: This simple, rapid, easy, and noninvasive urinary trypsinogen-2 test can diagnose or rule out most cases of acute pancreatitis.

Digital microfluidic platform for multiplexing enzyme assays: implications for lysosomal storage disease screening in newborns.

BACKGROUND: Newborn screening for lysosomal storage diseases (LSDs) has been gaining considerable interest owing to the availability of enzyme replacement therapies. We present a digital microfluidic platform to perform rapid, multiplexed enzymatic analysis of acid α-glucosidase (GAA) and acid α-galactosidase to screen for Pompe and Fabry disorders. The results were compared with those obtained using standard fluorometric methods. METHODS: We performed bench-based, fluorometric enzymatic analysis on 60 deidentified newborn dried blood spots (DBSs), plus 10 Pompe-affected and 11 Fabry-affected samples, at Duke Biochemical Genetics Laboratory using a 3-mm punch for each assay and an incubation time of 20 h. We used a digital microfluidic platform to automate fluorometric enzymatic assays at Advanced Liquid Logic Inc. using extract from a single punch for both assays, with an incubation time of 6 h. Assays were also performed with an incubation time of 1 h. RESULTS: Assay results were generally comparable, although mean enzymatic activity for GAA using microfluidics was approximately 3 times higher than that obtained using bench-based methods, which could be attributed to higher substrate concentration. Clear separation was observed between the normal and affected samples at both 6- and 1-h incubation times using digital microfluidics. CONCLUSIONS: A digital microfluidic platform compared favorably with a clinical reference laboratory to perform enzymatic analysis in DBSs for Pompe and Fabry disorders. This platform presents a new technology for a newborn screening laboratory to screen LSDs by fully automating all the liquid-handling operations in an inexpensive system, providing rapid results.

Novel peptidoglycan-based diagnostic devices for detection of wound infection.

Detection of wound infection is based on evaluation of the well-known signs of inflammation like rubor (redness), calor (heat), tumor (swelling), and dolor (pain) by medical doctors and/or time-consuming procedures requiring special machinery. There is currently no rapid diagnostic device available for the indication of wound infection, which would especially be helpful in home care of chronic ulcer patients. In this study, a new concept for a fast diagnostic tool for wound infection based on lysozyme and elastase triggered release of dye from a peptidoglycan matrix was investigated. The matrix consisted of alginate/agarose and peptidoglycan covalently labeled with Remazol brilliant blue. Lysozyme activity in postoperative wounds and decubitus wound fluids was significantly elevated upon infection (4830 ± 1848 U mL(-1)) compared to noninfected wounds (376 ± 240 U mL(-1)). Consequently, incubation of 8% (w/v) labeled agarose/peptidoglycan blend layers with infected wound fluid samples for 2 h at 37 °C resulted in a 4-fold higher amount of dye released than measured for noninfected wounds. For alginate/peptidoglycan beads, a 7-fold higher amount of dye was released in case of infected wound fluid samples compared to noninfected ones. Apart from lysozyme, proteases [i.e., gelatinase matrix metalloproteinase MMP-2 and MMP-9 and elastase] were detected in wound fluids (e.g., using Western blotting). When dosed in ratios typical for wounds, a slight synergistic effect was measured for peptidoglycan hydrolysis (i.e., dye release) between lysozyme and these proteases. Incubation of a double-layer system consisting of stained and nonstained peptidoglycan with infected wound fluids resulted in a color change from yellow to blue, thus allowing simple visual detection of wound infection.

Validity of a point of care device (Cholestech LDX) to monitor liver enzyme activity (aminotransferase measures) during a clinical trial.

BACKGROUND: Serum transaminase activity is a common measure of liver injury used in clinical trials. The use of a point of care device to monitor serum transaminases would allow immediate evaluation of this safety endpoint and may be less expensive than standard laboratory testing. PURPOSE: The objective of this study was to compare a point of care transaminase test to a standard laboratory measurement. METHODS: Subjects were healthy adults participating in a clinical trial measuring the effects of therapeutic doses of acetaminophen on serum transaminase activity. For this study, serum transaminase activity was determined every 3days for 14days. At each measurement, a sample was sent to the clinical laboratory for measurement and also analyzed using a point of care device (Cholestech LDX, Hayward CA). The results were compared using a Bland-Altman plot to identify bias and we also measured the agreement between the techniques for categorizing samples as "low", "normal" or "elevated". RESULTS: One hundred thirty three samples from 35 subjects were compared. The 95% confidence interval for the limits of agreement between the LDX and the clinical laboratory was -8.46 to 27.09IU/L. Agreement for classification as low, normal or elevated was moderate between the two methods (Kappa=0.37). CONCLUSION: The point of care device provided moderate agreement with the laboratory transaminase measurement. However, use of the device would have resulted in misclassification of approximately 1/3 of samples. We do not recommend this point of care device for the measurement of serum transaminases in clinical trials.

Stopped-flow enzyme assays on a chip using a microfabricated mixer.

This paper describes a microfabricated enzyme assay system including a micromixer that can be used to perform stopped-flow reactions. Samples and reagents were transported into the system by electroosmotic flow (EOF). Streams of reagents were merged and passed through the 100-pL micromixer in < 1 s. The objective of the work was to perform kinetically based enzyme assays in the stopped-flow mode using a system of roughly 6 nL volume. Beta-galactosidase (beta-Gal) was chosen as a model enzyme for these studies and was used to convert the substrate fluorescein mono-beta-D-galactopyranoside (FMG) into fluorescein. Results obtained with microfabricated systems using the micromixer compared well to those obtained with an external T mixing device. In contrast, assays performed in a microfabricated device by merging two streams and allowing mixing to occur by lateral diffusion did not compare well. Using the microfabricated mixer, Km and kcat values of 75 +/- 13 microM and 44 +/- 3 s(-1) were determined. These values compare well to those obtained with the conventional stopped-flow apparatus for which Km was determined to be 60 +/- 6 microM and kcat was 47 +/- 4 s(-1). Enzyme inhibition assays with phenylethyl-beta-D-thiogalactoside (PETG) were also comparable. It was concluded that kinetically based, stopped-flow enzyme assays can be performed in 60 s or less with a miniaturized system of roughly 6 nL liquid volume when mixing is assisted with the described device.

Cholinesterase measurements with an automated kit.

BACKGROUND: The Test-mate kit determines acetylcholinesterase (AChE, EC 3.1.1.7) and hemoglobin content of a drop of blood, displaying enzyme activities normalized to 25 degrees C. Previous models produced inconsistent results at different temperatures. This report focuses on the current model, ChE 400, and two instruments of a previous OP model. METHODS: AChE activities were determined by the Ellman assay, using the three kits and a 96-well microplate reader. Temperatures ranged from 10 to 37 degrees C. Fetal bovine serum was the source of AChE. RESULTS: Normalized activities decreased below 20 degrees C in the ChE model and below 25 degrees C in the OP models. Activities of the same serum sample differed between the three Test-mate kits, ranging from 1.03 to 1.49 micromoles/min/ml. Percent errors were greater than with the microplate reader at all temperatures. CONCLUSIONS: Neither we nor the manufacturer recommend the current Test-mate model for fieldwork. Nevertheless, there have been field measurements with Test-Mate kits, and we recommend that an enzyme activity standard be run in parallel with their use.

Multicenter harmonization of common enzyme results by fresh patient-pool sera.

A region consisting of 19 clinical laboratories harmonized their calibration of seven common enzymes by using fresh patient-pool sera. One of the laboratories was chosen to act as Regional Reference Laboratory (RRL). This laboratory used internationally accepted (mostly IFCC) methods at 37 degrees C, with an intralaboratory CV < or = 2.5%. First, the reference ranges of the RRL were verified by analysis of a reference population and calculation of the results by a parametric method. Next, all laboratories, including the RRL, received six patient-pool sera and analyzed them at the same time on the same date. Enzyme calibration factors at each laboratory were converted on the basis of the slope, and occasionally the intercept, of regression analysis with the RRL and the individual laboratory. Before harmonization, the interlaboratory CVs varied from 16.9% to 61.6%. After harmonization, CVs decreased to between 5.0% and 9.5%. These results proved to be reproducible over a period of more than a year. Using internationally accepted inaccuracy and imprecision criteria, the achieved interlaboratory CVs permit the use of one set of reference ranges by all participating laboratories. Certified Reference Materials were analyzed, resulting in interlaboratory CVs as low as those achieved with patient-pool sera. These materials can act as commutable reference preparations, except for creatine kinase.

Differences in molar absorptivity of 4-NP with the reaction solution and apparatus affect ALP measurement.

We examined the differences in molar absorptivity of 4-NP obtained using different kits for ALP measurement and different instruments. The apparent molar absorptivity of 4-NP in the same reaction solution determined by six different instruments was 15.98, 16.72, 16.06, 17.00, 16.27, 17.62 and that using four different reaction solution kits for ALP with the same instrument was 16.90, 17.38, 17.72, 16.11. We measured ALP in three serum samples with six instruments using the same kit and in twelve serum samples with the same instrument using four kits. ALP activities measured using the same molar absorptivity value differed with the instrument(p < 0.01). However, those measured using the apparent molar absorptivity value for each instrument revealed no significant differences(p > 0.05). In conclusion, we suggest that standard material should be contained in each kit for enzyme measurement and the apparent epsilon for each kit and instrument should be obtained to minimize the systematic error caused by using the same epsilon in different laboratories.

Reagents for measuring intracellular enzyme activity with flow cytometry.

The line of enzyme substrates described, together with the flow cytometer, bring a simplified method of measuring intracellular enzyme activity to the research laboratory. They are optimized for use in flow cytometry but can also be adapted to other fluorescent detection methods (e.g., spectrofluorometry, fluorescent microscopy, and image analysis) (Figure 5). The large number of enzymes that can be measured with the reagents (currently 37), together with the automation and multiparametric capabilities of flow cytometry, offer many advantages over conventional methods of cell characterization. They also expand the potential of functional assays for studying many normal physiological and disease processes.

Optimización del análisis de ácidos biliares séricos por método enzimático fluorométrico / Improvement of an enzymatic fluorometric assay for serum bile acids

Con el objeto de optimizar la determinación fluorométrica de los ácidos biliares séricos (ABS) en cuanto a selectividad y sensibilidad, se desarrolló una metodología de preparación de muestra y preconcentración utilizando columnas de extracción en fase sólida (SPE-C18). Previa desproteinización del suero con acetonitrilo frío, la fase orgánica evaporada y reconstituida con acetonitrilo: agua (3:70), se aplicó a una columna SPE-C18 y los ABS fueron eluidos con metanol. En el extractivo metanólico, evaporado a sequedad y reconstituido con metanol se dosaron los ABS por método enzimático fluorométrico empleando 3Ó-hidroxiesteroide deshidrogenasa, ß-NAD, diaforasa y resazurina. En la validación de la preparación de muestra se utilizó [24-14C] ácido glicocólico. La recuperación fue del 89,0 ñ 1,3 por ciento (SD), con DSR de 1,4 para n=9 (3 días). Se determinaron los ABS en sujetos controles, resultando un valor medio de 2,61 ñ 0,39 µM (SEM) (n=27). La metodología propuesta combina las siguientes ventajas: aumento de la selectividad del método enzimático, eliminación de interferencias y preconcentración de los ABS liberados, previamente, de la unión a proteínas plasmáticas