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CAP Home > CAP Reference Resources and Publications > CAP TODAY > CAP TODAY 2009 Archive > Q & A for October 2009
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  Q & A

 

 

 

 

October 2009

Editor:
Fredrick L. Kiechle, MD, PhD

Question Q. It has been estimated that 30 percent of the laboratory staff may be out at one time during the expected swine flu epidemic. Are there general protocols or recommendations (for example, modifications of general test ordering and processing) and personnel policies (other than vaccination) regarding staffing and operating the laboratory during this anticipated epidemic?

A. This is a difficult question to answer and have it apply to any one specific clinical laboratory. Generally speaking, it is wise for a laboratory to have a disaster preparedness policy so that when something does happen, there is a procedure/algorithm that is followed. To bring the perspective of our laboratory and health care system, we are in south Florida (sandwiched between Miami to the south and Fort Lauderdale to the north). Our lab has in place a hurricane preparedness policy that will be adapted to address and prepare for the staff shortages that are estimated to occur in this respiratory virus season.

It is hard to predict how the volumes of laboratory tests will be affected. Certainly, one would expect respiratory virus testing to increase. This increased workload would put a lot of stress on a lab with a 30 percent shortage of staff. Therefore, certain non-critical tests that are normally performed in-house would have to be sent out to a reference laboratory or testing frequency may need to be reduced. If the reference labs are affected, they may also change how often certain tests are performed, thereby increasing the turnaround time even more. Changes in laboratory testing must be determined and will vary depending on the laboratory and the associated health care institution(s). It would be essential to continually educate the clinicians and other hospital staff so they can be made aware of the changes.

Personnel policies would have to be dictated by the institution and thus, here too, it is difficult to discuss specifics. Issues such as how the lower staffing levels could potentially be scheduled would have to be addressed within the laboratory’s disaster preparedness policy. What might have to be considered is the requirement of having the 2009 pandemic influenza A (H1N1) vaccine, when it becomes available. The Institute of Medicine recently published recommendations regarding the use of personal protective equipment for health care workers, which includes laboratory staff.1

Unfortunately, these issues would be dealt with in real-time as the staffing shortages begin to increase.

Reference

1. Institute of Medicine. Respiratory protection for healthcare workers in the workplace against novel H1N1 influenza A: A letter report. Washington, DC: The National Academies Press; 2009 (www.nap.edu/catalog.php?record_id=12748).

Rodney C. Arcenas, PhD, D(ABMM)
Clinical Scientist – Microbiology/Molecular Pathology Consultants of
South Broward
Memorial Healthcare System
Hollywood, Fla.

Question Q. We currently use a venous draw for maternal glucose tolerance testing. If we switched to performing AccuChek testing for each mother, would we still get the results the physician is looking for to make a diagnosis?

A. According to the American Diabetes Association, or ADA, approximately seven percent of pregnancies are complicated by diabetes mellitus, or DM.1 A fasting plasma glucose value greater than 126 mg/dL or a casual plasma glucose greater than 200 mg/dL if confirmed on a subsequent day establishes the diagnosis of DM. Women of average or high risk should be evaluated even in the absence of a diagnostic level of hyperglycemia.

The ADA has recommended two possible approaches (protocols and diagnostic criteria are provided in reference No. 1). The first is the one-step approach. For this approach, perform a diagnostic oral glucose tolerance test, or OGTT, which uses a 100- or 75-g oral glucose load as described in reference No. 1. The second is the two-step approach. For this approach, perform a screening glucose challenge test consisting of a plasma or serum glucose one hour after administering a 50-g oral glucose load. In the case of women where the one-hour glucose exceeds a threshold value, a diagnostic OGTT using a 100- or 75-g oral glucose load should be performed.1

A variety of methods and sample types are available for measuring glucose levels in blood specimens. Sample types include venous plasma and serum, capillary specimens obtained by fingerstick methods, and other sample types such as arterial blood. The measured glucose value is known to differ in capillary versus venous blood. Typically, capillary blood yields higher values.2 The difference in values may be small in the fasting state but can be as high as +15 to 26 percent following a meal or glucose load.2–4 Almost all meters available in the United States, how-ever, have been calibrated to give a result similar to that of a venous plasma sample.

ADA criteria for the diagnosis of DM, including criteria for DM using the OGTT, have explicitly used venous plasma samples in published guidelines. The use of other sample types, such as capillary glucose values, may have appeal from the perspective of simplicity and patient comfort, but this practice should be discouraged given the potentially significant (and at times unpredictable) differences between capillary and venous glucose values. Given the calibration of most meters to venous plasma, the major objection is the relative inaccuracy of the meters, especially in the lower range of glucose values. These differences could have a significant effect on the sensitivity and specificity of the OGTT, resulting in patients being misclassified with regard to the presence or absence of DM. Some data suggest that, in the hands of well-trained personnel, handheld glucose meters can be used in gestational diabetes screening.4 Other studies, however, have reached an alternative conclusion. In the absence of a clear consensus from an organization such as the ADA, it is therefore probably best to avoid using handheld glucose meters when performing an OGTT.

References

1. American Diabetes Association. Gestational diabetes mellitus. Diabetes Care. 2003;-26:S103–S105.

2. Simmons DA. Comments on evaluation of five glucose meters by Thomas et al. Diabetes Technol Ther. 2008;10:415.

3. Stravrianos C, Anastasiou E. Oral glucose tolerance evaluation with forearm and fingertip glucose measurements in pregnant women. Diabetes Care. 2004;27:627–628.

4. Melnik J, Potter JL. Variance in capillary and venous glucose levels during a glucose tolerance test. Am J Med Technol. 1982;48:543–545.

Kent Lewandrowski, MD
Associate Chief of Pathology
(Director of Clinical Services, Anatomic and Clinical Pathology)
Massachusetts General Hospital
Associate Professor of Pathology
Harvard Medical School
Boston

Question Q. Our laboratory is in a small rural hospital with an active emergency department, and we would like advice on what to include in our cardiac profiles. Patients with chest pain of cardiac origin are often referred by Life Flight to a regional care center, which is time-consuming, expensive, and not risk free. The standard screening tests we use are CK-MB and troponin, and the results of these assays occasionally conflict. Sometimes the CK-MB is elevated with both a normal total CK and troponin level. We have attempted to address this by changing our assay platform for CK-MB from the Roche Cobas Integra to the Roche Elecsys because of the possibility of false-positive CK-MB results owing to hemolysis. The other issue has to do with patients who have both an elevated troponin and CK-MB level initially and are then held for observation. If these patients have recurrent symptoms in the next 48 hours, the troponin level may still be elevated and physicians would like the CK-MB, which falls faster, to be done to see if there is a secondary rise.

Our problem in the laboratory is that the troponin assay is far superior, and we are concerned about the cost and risk of sending to a tertiary center patients with minor symptoms, a normal EKG, and a minimal secondary CK-MB rise. We polled a group of small regional centers and found that four have dropped the CK-MB assay, two offer it but rarely use it, and four still offer it.

A. For diagnosis of acute myocardial infarction, or MI, assays for cardiac troponin are more clinically specific and sensitive than CK-MB. The National Academy of Clinical Biochemistry, or NACB, has said that “Cardiac troponin is the preferred marker for the diagnosis of MI. Creatine kinase MB (CK-MB) by mass assay is an acceptable alternative when cardiac troponin is not available (Level of Evidence: A).”1 Results of CK-MB mass assays provide redundant information to troponin when contemporary cutoff limits, that is, the 99th percentile, are used. The NACB has also opined that CK-MB activity assays “should not be used as biomarkers for the diagnosis of MI (Level of Evidence: C),” which supports your laboratory’s switch from the Cobas Integra (immunoinhibition assay) to the Elecsys (mass assay).

In these harsh economic times, many laboratories have discontinued CK-MB testing, as you mention. This observation is supported by declining subscriptions to the CAP’s “Cardiac Marker” proficiency test in recent years. However, the elimination of the CK-MB test has not been without criticism. Given that troponin remains increased for several days longer than CK-MB, some cardiologists have argued to retain CK-MB for detecting reinfarction, which occurs in about 10 to 20 percent of MI cases. However, in a series of reinfarction case reports, Apple, et al., showed that troponin was equally effective as CK-MB for detecting a secondary rise in biomarker value, despite the fact that the troponin result does not necessarily return to reference values.2 If this evidence is insufficient, the clinical laboratory can suggest serial testing for total creatine kinase to detect a secondary rise in enzyme results. While CK is not as specific as CK-MB, it is equally sensitive for detecting myocardial injury. As CK is important for detecting skeletal muscle injury, there is no recommendation or suggestion to remove total CK from a laboratory’s test offering.

References

1. Morrow DA, Cannon CP, Jesse RL, et al. National Academy of Clinical Biochemistry laboratory medicine practice guidelines: clinical characteristics and utilization of biochemical markers in acute coronary syndromes. Clin Chem. 2007;53:552–574.

2. Apple FS, Murakami MM. Cardiac troponin and creatine kinase MB monitoring during in-hospital myocardial reinfarction. Clin Chem. 2005;51:460–463.

Alan H.B. Wu, PhD
Chief, Clinical Chemistry Laboratory
San Francisco General Hospital
Professor of Laboratory Medicine
University of California
San Francisco

Consultant, CAP Toxicology
Resource Committee


Dr. Kiechle is medical director of clinical pathology, Memorial Healthcare, Hollywood, Fla.
 
 
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