Optimal Utilization of Laboratory Testing
Published: November 2011
Hot Topic Q&A is an opportunity for viewers to submit questions to the Hot Topic presenter. The opportunity to submit questions for this topic is now closed.
The following questions were submitted by viewers and answered by the presenter, James S. Hernandez, MD, MS, Medical Director of Laboratories and Chair of the Division of Laboratory Medicine at Mayo Clinic Arizona. He is also an Assistant Professor of Laboratory Medicine and Pathology at Mayo Clinic.
Questions are presented as submitted (unedited).
Do you think that procalcitonin is well supported in the literature to be a useful test for assessing/ monitoring septicemia? It is not appropriate for send-out since its usefulness is more immediate in nature. Should we add this to our test menu?
This is a timely question for us. We are examining procalcitonin for our practice now. In our approach we use literature-supported evidence first. For procalcitonin, the literature-supported evidence is increasing on the utility of procalcitonin. We next evaluate the clinical utility and impact on patient care. At first, our clinicians were mixed in their response on whether they would use procalcitonin if we offered this assay, but over the last year, consensus has developed that procalcitonin may add value in assessing bacterial sepsis. One difficulty is that there aren’t many platforms for this assay. We have spoken to major vendors and they do not plan to immediately offer procalcitonin on their instruments, so we would need to purchase a separate platform. Finally, as you point out, this test must be done onsite and its usefulness is negated if it is sent out as a reference test. Given all of these factors, we have placed procalcitonin on our list of tests to be developed for our practice in the near future. You may consider a similar approach with your medical staff to assess whether or not to offer procalcitonin in your practice.
What does the evidence-based literature say about Widal Test, given that it is widely used in resource constrained countries?
According to the Manual of Molecular and Clinical Laboratory Immunology, 7th edition, edited by Detrick, Hamilton and Folds, page 455, the Widal tests measure agglutinating antibodies to serovar Typhi H and LPS antigens and are said to be “classic assays for the serodiagnosis of acute typhoid fever.” Though they are widely used worldwide, the validity of these tests has been questioned, even in areas where typhoid fever is endemic. I would refer you to this textbook, which offers guidance on the usefulness and limitations of the Widal tests.
In addition, the Manual of Clinical Microbiology, 10th Edition (2011), states that the Widal test, which measures agglutinating antibodies to the O and H antigens of Salmonella serotype Typhi, produces false-negative and false-positive reactions and does not provide a definitive diagnosis of individual cases of infection. Two other rapid serodiagnostic tests have proved more useful than the Widal test for the serodiagnosis of typhoid fever (Tubex [IDL Biotech, Sollentuna, Sweden] and TyphiDot [Malaysian Bio-Diagnostics Research Sdn. Bhd., Kuala Lumpur, Malaysia]). These tests are most useful in areas where typhoid fever is endemic and are less useful in the United States, where typhoid fever is rare. Neither of these tests is FDA approved, and TyphiDot is not available in the United States.
(My thanks to Tom Grys, Ph.D., Director of Microbiology at Mayo Clinic in Arizona, who provided answers for this question.)