Plasma separation from blood specimen

Blood specimens of approximately 5 mL were collected on two separate days during the week preceding the study. Additional blood specimens of approximately 5 mL each were collected approximately 24 and 48 hr after the start of the study. These blood specimens were drawn and assayed for plasma cholinesterase activity by personnel from the Michigan Division Medical Department of The Dow Chemical Company. 

Blood is most commonly used for the analysis of APs as drug concentrations in blood represent a more accurate correlation with pharmacological effects than in any other specimen. Plasma or serum is usually obtained from clinical samples, as blood cells can easily be separated from liquid components to create a cleaner ... 

It is reasonable to question whether the distribution of the estimates of a drug concentration in a blood specimen might be approximated by the normal distribution. Table 1 presents the results of repeated analyses of a specimen of interference-free plasma spiked to contain a known amount of drug. These data are taken from a comparative bioavailability study in which single doses of an unmarketed generic product and the marketed brand product of a drug were administered on separate occasions to healthy males. The values presented are the first of duplicate determinations of a quality control (QC) specimen that was included with each batch of subject specimens. This was done to verify that the in-process accuracy and precision of the assay method were consistent with the values observed during the assay validation. 

Although delays of a specimen in transit from a patient in a hospital to the laboratory are usually short, the time elapsing from the separation of serum and cells until analysis may be considerable. The specimen must be properly treated both during its transport to the laboratory and from the time the serum has been separated until it is analyzed. For some tests, specimens must be kept at 4 C from the time the blood is drawn mitil the specimens are analyzed, or until the serum or plasma is separated from the cells. Examples are specimens for ammonia and blood gas determinations, such as PCO2, PO2, and blood pH (see Chapter 27). Transfer of these specimens to the laboratory must be done by placing the specimen container in ice water. Specimens for acid phosphatase, lactate and pyruvate, and certain hormone tests (e.g., gastrin and renin activity) should be treated the same way. A notable decrease in pyruvate and increase in lactate concentration occurs within a few minutes at ambient temperature (see Chapter 25). 

Compared to other drugs of abuse, analysis of cannabinoids presents some difficult challenges. THC and 11-OH-THC are highly lipophilic and present in low concentrations in body fluids. Complex specimen matrices, i.e., blood, sweat, and hair, may require multi-step extractions to separate cannabinoids from endogenous lipids and proteins. Care must be taken to avoid low recoveries of cannabinoids due to their high affinity to glass and plastic containers, and to collection devices for alternate matrices (Blanc et al. 1993 Bloom 1982 Christophersen 1986 Joern 1992). THC and THCCOOH are predominantly found in the plasma fraction of blood, where 95% to 99% are bound to lipoproteins. Only about 10% of either... 

Blood specimens collected in tubes containing either fluoride or heparin are satisfactory for the measurement of creatinine. Ammonium heparin, however, should not be used to collect blood specimens, if the assay is to be performed with a coupled-enzyme procedure that measures ammonia. To minimize in vitro ammonia formation, serum or plasma should be promptly separated from the cells for creatinine assay procedures that depend on ammonia generation. Creatinine is fairly stable in serum stored at 4°C for at least 1 week. 

There is no experimental evidence that steroid hormone concentrations in serum are different from those in plasma. However, rapid separation of red blood cells in the specimen is important because red blood cells at room temperature can alter plasma concentrations of active steroid hormones red blood cells degrade estradiol to estrone and cortisol to cortisone, and they can adsorb testosterone. 

NAA has become more common, particularly where multielement analysis is required [57-59]. Some sample preparation is usually necessary. For example, a blood sample preparation will require separation of the serum and plasma followed by freeze-drying of the specimen before irradiation. Afterward samples were wet-ashed and fractionated on various columns before the y spectra from each fraction could be obtained [60]. 

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