The available TG lipase assays have limitations for the determination of plasma LPL activity in one or another of the aspects of sensitivity, substrate stability, and environmental friendliness. For example, the conventional radiometric assay, using 3 H-or 14 C-labeled trioleoyl glycerol as substrate, requires separation of the released labeled FAs, is time-consuming with low throughput, and, particularly owing to the use of radiolabel, is limited to research applications ( 11 ). Fluorescence-based assays using coumarin derivatives are attractive because they fl uoresce only after conversion to lipolytic products. However, the derivatives are unstable, requiring frequent substrate preparation, and are hydrolyzed nonspecifi cally by enzymes other than LPL ( 12 ). Another commonly used assay, the titrimetric method, is not very sensitive ( 12 ).Heparin-treated plasma contains two additional members of the TG lipase family, hepatic lipase (HL) and endothelial lipase (EL), with biological roles different from that of LPL ( 13 ). These also contribute to TG hydrolysis, complicating data interpretation. Strategies that have been employed to dissect out LPL-specifi c activity have limitations. Under high-salt conditions, LPL activity is inhibited, suggesting that the difference between low-and high-salt measurements will yield LPLspecifi c activity. However, high salt also affects HL activity ( 14 ). Determination of activity in the presence and absence of apoC-II, a specifi c activator of LPL, is another approach. The limitation of this approach is that the interaction between these two proteins is affected by sphingomyelin ( 15 ). A third approach, inhibition of human LPL by the 5D2 neutralizing antibody, has documented complications ( 16 ).Here, we report development of a novel, homogenous LPL TG lipase assay employing a commercially available Lipoprotein lipase (LPL), which hydrolyzes triglycerides (TGs) to release free fatty acids (FFAs), is the rate-limiting enzyme controlling plasma TG levels. Hydrolysis of TGs is essential for energy storage and utilization, whereas variations in TG/FFA levels have a variety of clinical implications that have been extensively reviewed, (see, for example, Refs. 1-3 ). In evaluating LPL function in heparin-treated plasma, measurement of enzyme activity is more valuable than quantifi cation of protein concentration by immunoassay. The latter does not differentiate between: active homodimer and inactive monomer ( 2, 3 ); active enzyme and inactive, proteolytically cleaved enzyme ( 4 ); the presence or absence of activity-modulating plasma lipid components ( 5 ) or proteins of clinical interest such as activators apolipoprotein C-II (apoC-II) ( 6 ) and apoA-V ( 7 ) and inhibitors apoC-I and apoC-III ( 8 ); angiopoietin-like protein-3 ( 9 ) and angiopoietin-like protein-4 (ANGPTL4) ( 10 ).
Chest pain is commonly reported in emergency departments, and a thorough clinical history is important in distinguishing the etiology. This case highlights Kounis syndrome, a histamine-mediated coronary vasospasm leading to myocardial injury, due to scombroid fish poisoning. ( Level of Difficulty: Beginner. )
Purpose: Appropriate use criteria (AUC) defines the appropriateness of imaging procedures for specific clinical scenarios to promote evidence-based utilization and improve cost-effective care. The goal of this study was to assess the diagnostic yield and downstream health care resource utilization according to the AUC categorization for coronary computed tomography angiography (CCTA) in emergency department (ED) patients presenting with chest pain. Materials and Methods: A total of 789 consecutive patients in the ED with chest pain and no known coronary artery disease (CAD) who underwent CCTA were classified as appropriate, uncertain, or inappropriate use according to the 2010 AUC. We abstracted index and 30-day data from the electronic medical record to determine diagnostic yield (rate of obstructive CAD and revascularization) and health care resource utilization (downstream stress test and 30-d hospital return rate). Results: Rates of appropriate, uncertain, and inappropriate utilization were 48.4%, 48.8%, and 2.8%. Among appropriate, uncertain, and inappropriate classifications, rates of obstructive CAD were 9%, 8%, and 32% (P=0.002); rates of revascularization were 3%, 1%, and 36% (P<0.001); downstream stress test utilization rates were 5% versus 5% versus 14% (P=0.17), and 30-day hospital return rates were 6% versus 6% versus 5% (P>0.99), respectively. Conclusions: Appropriate and uncertain uses were associated with low diagnostic yield compared with inappropriate use; however, our findings do not demonstrate differences between appropriate use categories with respect to downstream health care resource utilization. Further studies are needed to define the role of AUC for CCTA in the ED setting.
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