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Check Sample Abstracts1 Fetal Lung Maturity Testing Clinical Chemistry No. CC 08-1 (CC-367)2 Alkaline Phosphatase Isoenzyme Analysis: Guiding the Differential Diagnosis of Elevated Serum Total Alkaline Phosphatase Clinical Chemistry No. CC 08-2 (CC-368)3 Indirect Phlebotomy: Is It Good Practice? Clinical Chemistry No. CC 08-3 (CC-369)

David Alter MD, David S. Bosler MD, James Nichols PhD, DABCC, FACB, David G. Grenache PhD, Raymond E. Karcher PhD, Aparna Rajadhyaksha MD, Sandra Camelo-Piragua MD, Carol Rauch MD, PhD, FACP
DOI: http://dx.doi.org/10.1309/AJCPCW0RNBEZVB2G 286 First published online: 1 February 2009

Abstract

The following abstracts are compiled from Check Sample exercises published in 2008. These peer-reviewed case studies assist laboratory professionals with continuing medical education and are developed in the areas of clinical chemistry, cytopathology, forensic pathology, hematology, microbiology, surgical pathology, and transfusion medicine. Abstracts for all exercises published in the program will appear annually in AJCP.

1 Fetal Lung Maturity Testing Clinical Chemistry No. CC 08-1 (CC-367)

Abstract

Neonatal respiratory distress syndrome (RDS) is a disorder of pulmonary immaturity with a high mortality characterized by low levels of pulmonary surfactant. Gestational age determines risk based on concentration of pulmonary surfactant, ie, as gestation progresses the concentration of pulmonary surfactant increases. As a result, newborns delivered at fewer than 28 weeks have a more than 60% risk of RDS, whereas those delivered at more than 34 weeks have a less than 5% risk of RDS. In situations where gestational age alone is not sufficient to determine RDS risk and preterm delivery is medically needed, amniotic fluid analysis can be performed to determine pulmonary surfactant concentration. Four common methods are the lecithin-sphingomyelin ratio, phosphatidylglycerol measurement, surfactant-albumin ratio, and lamellar body count. All of these tests have excellent negative predictive values but poor positive predictive values, ie, they are great at confirming maturity but poor at confirming immaturity.

2 Alkaline Phosphatase Isoenzyme Analysis: Guiding the Differential Diagnosis of Elevated Serum Total Alkaline Phosphatase Clinical Chemistry No. CC 08-2 (CC-368)

Abstract

The measurement of alkaline phosphatase (ALP) has long been used in clinical medicine, primarily to aid the diagnosis and monitoring of liver and bone diseases. Its diagnostic utility is limited by the enzyme’s wide tissue distribution and by a variety of potential nonpathologic causes. Isoenzyme analysis is one of several tools available to the clinician hoping to further characterize an elevated total ALP. It provides differentiation among liver, bone, intestinal, placental, and tumor-related forms as the cause of an elevation. The case presents a patient with persistent elevated ALP and atypical bands in the isoenzyme electrophoresis gel. An atypical ALP may be the result of a macroenzyme, which, if present, complicates interpretation of the test result and may cause additional, unnecessary testing or procedures. Recognizing and reporting a macroenzyme is an important service the clinical laboratorian can provide a clinician.

3 Indirect Phlebotomy: Is It Good Practice? Clinical Chemistry No. CC 08-3 (CC-369)

Abstract

Indirect phlebotomy, the collection of blood samples through vascular infusion devices, is a common practice adopted to minimize needle-stick pain and discomfort in hospitalized patients. However, this practice can lead to alteration of the specimen and medical errors associated with misrepresentation of the blood test values. Among the possible problems, dilution or concentration of a particular analyte may occur, depending on the contents of the line’s infusate. Although some studies may indicate that blood collection from lines can be acceptable for isolated laboratory tests, there are insufficient data to demonstrate the reliability of line draws as routine practice. Use of lines for specimen collection should be reserved only for those patients with truly poor vascular access or those patients who require multiple phlebotomies in a short time period. Samples should be collected from lines only under a direct physician order, with careful attention to technique and established protocols that take many variables into account, including the analytes, contents of the line, type of line, discard blood volume, time interval between interruption of infusion and sampling, and catheter size. Even with careful attention to these details, clinicians must remain wary of the potential for medical errors related to misinterpretation of laboratory test results based on such samples.

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