Flow cytometric procedures have replaced several well established clinical laboratory tests.  In the last issue of the eNewsletter Marc Golightly described the DHR test for chronic granulomatous disease and mentioned how this flow cytometric test has replaced the Nitroblue tetrazolium dye reduction test (NBT).  This issue of the eNewsletter provides a few other examples. 

For the Case Study Interpretation (CSI) section of the eNewsletter Andrea Illingworth from Dahl-Chase Diagnostic Services, Bangor, Maine, provides an example of testing for paroxysmal nocturnal hemoglobinuria (PNH).  Flow cytometric testing for PNH replaced the acidified-serum lysis test (Ham test) many years ago, and is widely accepted as the gold standard for the diagnosis and monitoring of PNH.  However, many flow cytometry laboratories still offer a less than optimal PNH assay.  Andrea has been actively involved in optimizing flow cytometric testing for PNH and helped to develop the guidelines that were published last year in Cytometry Part B (Clinical Cytometry).

In this issue, Ros Ward from the Sheffield Teaching Hospitals Foundation Trust describes the anti-D flow cytometric test used at their institution as a replacement for the Kleihauer-Betke test for fetomaternal bleed, and Dan Marmer and Paul Kingma from Cincinnati Children’s Hospital Medical Center share their experience with the neutrophil CD64 index as a replacement for manual “band counts” in the evaluation for sepsis.  Given the superior performance of these flow cytometric tests, it’s surprising they have not been adopted more widely.  Indeed, Ros mentions in her article that “in June 2010, the UK National external quality assessment scheme for fetomaternal bleed testing had 45 participants registered for Flow cytometry as compared to 200 participants registered for the ‘Kleihauer-Betke’ acid elution method”.  Dan and Paul allude to a possible explanation in their article when they mention that the “full potential of the neutrophil CD64 assay is limited by the current time constraints of flow cytometry laboratory services and ultimately this assay will need to be transitioned to the main clinical laboratory before it can be implemented as part of every infection evaluation in the hospital”.  Such a transition might be achieved by incorporating a flow cytometer in the general lab. or possibly by expanding the flow-type capability of hematology analyzers. 

If a flow cytometer is available in your hematology laboratory you could consider using it for several other tests.  In this issue of the eNewsletter, Sindhu Cherian from the University of Washington, Seattle describes using a single 8-color antibody combination to perform a white blood cell differential with identification of monocytes, basophils, plasmacytoid dendritic cells, B-cells, NK-cells, T-cells, mature neutrophils, eosinophils, immature granulocytes, blasts, and nucleated red blood cells.  Before you read the article, try to guess which antibodies they used.  Although this 11-part flow differential is probably too expensive to be used for routine CBC testing, it could assist in specimens where morphologic classification is difficult, and also provides a useful reference procedure for white blood cell differential counting.  Flow cytometric methods are also considered to be the goal standard reference test for platelet counting as previously discussed in Cytometry Part B (Clinical Cytometry) 67B:1-5; 2005.  Another application for flow cytometric testing in the hematology laboratory is the identification of red blood cell membranopathies.  In an article recently accepted for publication in Cytometry Part B (Clinical Cytometry), currently available in “early view”, Prashant Warang and colleagues from the Indian Council of Medical Research, Mumbai, India, report their experience with a simple, inexpensive, flow cytometric osmotic fragility test and compare it with the eosin-5-maleimide dye flow cytometric test for red blood cell membranopathies.

So maybe it’s time to re-evaluate your flow cytometry test menu and the relationship of your flow cytometry and hematology laboratories.  But beware; doing this may result in the need for new test validation!  How should you go about implementing a new flow cytometry procedure, new instrumentation, or other procedural changes?  This is a theme common to several of the eNewsletter articles and will be the focus of the August issue.

 



Fiona Craig (Editor)
University of Pittsburgh School of Medicine,
Pittsburgh, PA, USA.