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January 2007 Q: Have studies been done on centrifuged serum separator tubes, or SSTs, that are sent through a pneumatic tube system to a main laboratory? Should the blood samples be recentrifuged? A: Pneumatic tube systems have been used to reduce turnaround time,1–3 close a satellite laboratory, and reduce the number of full-time employees in the lab.1 These carriers typically transport fresh whole blood specimens to the laboratory after the phlebotomist collects the specimens in non-anticoagulated or anticoagulated tubes.4,5 Because it takes up to an hour for most whole blood specimens to clot in non-anticoagulated collection tubes, the majority of such specimens sent through a pneumatic tube system will be unclotted or partially clotted when they arrive at the lab. To reduce the chance of damaging the cellular components in whole blood, a soft air cushion decelerates the pneumatic tube carriers as they approach the lab and gently drops them into the receiving area.3–5 However, the mechanical disruption to red cells may result in hemolysis,5 and the disruption to white cells from leukemic patients may result in pseudohyperkalemia.6 Phlebotomists can prevent air bubbles from developing in heparinized whole blood, which create perturbations in PO2 values,7 by placing the specimen in a pressure-sealed container before sending it through the pneumatic tube.8 The laboratory can determine whether delivery by courier or pneumatic tube led to disruption of red cell integrity by checking for an increase in potassium, lactate dehydrogenase, or hemolysis index in specimen pairs.2,5 In 1978, Poznanski et al4 reported that whole blood allowed to clot, but not centrifuged, prior to pneumatic tube transport had increased lactate dehydrogenase activity following arrival at the laboratory compared to freshly drawn whole blood. The tubes used in the study did not contain a gel separator. In 2004, Sodi et al5 reported that the degree of hemolysis was significantly increased during pneumatic tube transport in plain non-anticoagulated whole blood compared to similar collection tubes that contained a gel separator. These findings suggest that the gel protects against hemolysis by an undefined mechanism. No studies were found that compare the effect of pneumatic tube transport of centrifuged clotted whole blood on chemistry tests. Because recentrifugation of blood samples collected in gel separator tubes may cause a significant spurious increase in serum potassium, this practice is not recommended.9 References
Frederick L. Kiechle, MD, PhD Member, CAP Special Chemistry Q: Other than for the Roche Amplichip, has any use of microarrays been authorized? A: The promising clinical potential of microarrays is still evolving. Arrays allow simultaneous determination of the presence or absence of many nucleic acid targets and, in many cases, the relative amount of those targets when this level of complexity is clinically appropriate. DNA or RNA from the patient sample can be evaluated; the term “expression profiling” is frequently applied to RNA assessment. The Roche Amplichip detects the presence or absence of 29 2D6 and two 2C19 alleles that have differing effects on drug metabolism. There are standardized arrays that target thousands of single nucleotide polymorphisms, or SNPs, throughout the genome. Useful associations of polymorphisms with disease states could lead to broader use of SNP arrays if multiple polymorphisms within or among genes are needed. DNA deletions and duplication/amplification can be detected by comparative genomic hybridization, or CGH, arrays where the hybridization ratios of a patient versus a normal sample are assessed over multiple areas in the genome. This is an attractive approach to obtain a high-resolution karyotype for dosage alterations from selected chromosomal regions in genetic and oncology disorders. Expression profiling of RNA from cancers or other processes offers the most comprehensive and exciting application of arrays. This is because the RNA “signature” contains information derived from multiple independent tests and may offer insight into optimal therapeutic choices. Applications in development or under Food and Drug Administration review include tissue-of-origin identification for unknown primary tumors, classification of leukemia and lymphoma, as well as risk and therapeutic assessment for breast carcinoma. A concern with arrays has been difficulty reproducing results among laboratories. Recent studies demonstrate that independent laboratories can obtain relatively good reproducibility using commercially produced arrays. Where the number of targets is relatively small—for example, less than 100—alternative technologies may be useful. These include bead arrays, where individual hybridization reactions can be associated with beads of a defined color. It appears that array-based and other complex assays will require FDA clearance. Jeffrey A. Kant, MD, PhD Chair, CAP/ACMG Biochemical and Molecular Genetics |
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