Chromogenic substrates in haemostasis

Advances in knowledge of the structure-function relationships of the proteins involved in haemostatic pathways, have made it possible to synthesize small peptides which mimic the active site of many of the serine proteases concerned. Attachment to the cleavage site of such synthetic peptides, of a detector molecule such as para-nitroaniline which, when released, produces a coloured compound has enabled many of the enzyme reactions of haemostasis, and most of the co-factors and naturally-occurring inhibitors, to be individually and sensitively quantitated. Chromogenic substrate assays are very specific and overcome the criticism levelled at many conventional assays that, being based on the speed of formation or the rate of destruction of a fibrin clot, they frequently involve enzymatic reactions in addition to that being examined. Moreover, chromogenic substrate assays are generally simple and quick to perform and are readily automated. They are thus economical of manpower and, more importantly from the point of view of patient care, they permit the rapidly-changing status of those with acute derangements of haemostasis to be monitored more frequently and comprehensively than is possible using some conventional assays. Chromogenic substrate assays have some limitations, however. Since they mimic only a small portion of the natural substrate, they may not be sensitive to structural defects elsewhere in the molecule, and may thus not totally reflect biological activity. Though technically simple to perform, the defined incubation times and temperatures must be rigidly adhered to if reliable results are to be obtained.(ABSTRACT TRUNCATED AT 250 WORDS)     

Chromogenic factor VIII activity assay

Factor VIII (FVIII) may be measured by three different methodologies in the clinical laboratory: one‐stage clotting assay, two‐stage clotting assay, and chromogenic assay. These assays differ in ease of use, variety of reagents available, sensitivity to mild hemophilia A, and interference from lupus anticoagulants. This review will outline the methodology for each of the FVIII activity assays, with a discussion of assay interferences and variability. In some cases, chromogenic FVIII activity assays may be preferable to clot‐based assays, and these clinical situations will be reviewed as well. Am. J. Hematol. 89:781–784, 2014. © 2014 Wiley Periodicals, Inc.     

Chromogenic peptide substrate assays and their clinical applications

Chromogenic peptide substrates were first introduced into research laboratories in the early 1970s and were quickly utilised to develop assays for the determination of enzymes, proenzymes and inhibitors of the coagulation system. These assays were gradually introduced into coagulation and clinical chemistry laboratories as laboratory tools in the diagnosis and treatment of coagulation disorders. From the knowledge of the structures of the natural substrates attacked by enzymes other than those of the coagulation system or by synthesis and random screening, substrates for enzymes of the fibrinolytic, plasma and glandular kallikrein and complement systems were produced. These allowed various research groups to develop assays for components of these systems and subsequently led to the use of these assays in studies on various clinical conditions. Substrates for activated protein C ensured that assays for this enzyme and its inhibitors could be developed and introduced into the haematological routine. With the introduction of substrates for limulus lysate not only were assays for endotoxins in clinical samples produced but the control of all disposable products and injectables for endotoxin contamination can now be effected. Initially high costs and time-consuming manual assays were a hinderence to the general acceptance of the use of chromogenic peptide substrate assays and they were only used routinely in a few specialised laboratories. With the introduction of automated and microtitre plate methods however, these assays are are now available in most hospital laboratories. Since the first chromogenic peptide substrate was described thousands of articles have been published on the use of chromogenic substrate assays to measure proenzymes, enzyme activators, enzyme cofactors and inhibitors in blood and other body fluids in normal subjects and clinical material. We have endeavoured to cover as many of these as possible in this review.     

Postoperative Serratia marcescens endophthalmitis.

Endophthalmitis after ophthalmic surgery is a rare but serious complication. Postoperative endophthalmitis presents clinically with conjunctival erythema and lid edema with eye pain and decrease in visual acuity. Diagnosis requires invasive culture techniques because postoperative external eye cultures are not reflective of intraocular organisms. The most common pathogens causing postoperative endophthalmitis are staphylococci and streptococci. Less common organisms associated with exogenous endophthalmitis include gram-negative aerobic bacilli and fungi. We report a case of Serratia marcescens postoperative endophthalmitis in a normal host.     

Necrotic cellulitis by Serratia plymuthica

This case report describes an uncommon cellulitis caused by Serratia plymuthica in a patient treated with steroids. The evolution was favorable after surgical exploration with debridement and antibiotic treatment. This is the first case of necrotic cellulitis caused by S. plymuthica described in the literature.     

Community acquired sepsis by Serratia rubidaea

A 48-year-old male who had a past history of alcoholic pancreatitis and diabetes mellitus was admitted to our hospital due to chills and vomiting, on August 13, 1998. His body temperature was 38.0 degrees C, and he had the disturbance of consciousness, tachypnea, tachycardia and hepatomegaly with tenderness. Laboratory findings showed highly inflammatory reactions, DIC and hepatorenal dysfunction. Abdominal CT and US revealed multiple liver abscess with portal vein thrombus. Serratia rubidaea was detected in the blood culture. SBT/CPZ and TOB were administered and he recovered. This is a rare case of Serratia rubidaea sepsis. It is also necessary to pay attention to Serratia infections as well as S. marcescens.     

Serratia bacteremia: review of 118 cases

A review was conducted of 118 episodes of serratia bacteremia in cancer patients during a 16-year period. The infection occurred most commonly in patients with acute leukemia. Most patients acquired the infection in the hospital, and 61% had received antibiotic therapy during the preceding 10 days. Fever occurred in 90% of cases and shock in 18%. Thirty-eight percent of patients had concomitant pneumonia. Patients with shock, pneumonia, or hemorrhage had a substantially poorer prognosis. The response rate was 75% for patients who received appropriate antibiotics, 22% for those who received inappropriate antibiotics, and 29% for those who received no antibiotics. Patients who continued to have positive blood culture results while receiving appropriate antibiotic therapy had a poor diagnosis. Patients who received only an aminoglycoside had the poorest response rate among those who received appropriate therapy.     

Antikörpernachweis bei Serratia marcescens-Infektionen

Zusammenfassung Es wird über den Nachweis von Antikörpern gegen die homologen Stämme bei Serratia marcescens-Infektionen unter Heranziehung der Agglutination und Präzipitation berichtet. Die Untersuchungsergebnisse sprechen dafür, daß mit Antikörperbildung gerechnet werden muß, wenn invasive Verlaufsformen vorliegen. Die Agglutinationstiter lagen zwischen 1:40 und 1:640. Es ist anzunehmen, daß neben den gegen das O-Antigen gerichteten Antikörpern vom Patienten auch solche gebildet werden, die sich gegen bestimmte Antigene mit Ferment- und Toxincharakter richten.

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Antibody detection in infections with serratia marcescens

Summary A report is given on the detection by agglutination and precipitation of antibodies against homologous strains in infections with Serratia marcescens. The results of the investigation indicate that antibody formation is likely if invasive forms are present. The agglutination titers were between 1:40 and 1:640. It can be presumed that, in addition to the patient's antibodies against the O antigen, antibodies are also formed against certain antigens with the character of ferments or toxins.

     

Nonlinear Modeling of E-Type Ferrite Inductors Using Finite Element Analysis in 2D

We present here a modeling procedure for inductors with an E-shaped ferrite core valid for calculating the inductance of an equivalent circuit from the linear operating region to the saturation region. The procedure was developed using Finite Elements in 2D. We demonstrate that using a 2D section of the real core the results obtained are similar to the real ones, which solves the problem of convergence that appeared when E type cores were simulated in 3D, while also saving computational cost. We also discuss the effect of the gap-thickness on the magnetic properties. The data obtained by simulation are compared with experimental results.