Q&A column

Editor: Frederick L. Kiechle, MD, PhD

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Q. What is the minimum cutoff value for total nucleated cells and red blood cells in body fluids after which we need to perform cytospin?

A. October 2020—Automated complete blood cell counters are an accurate, precise, and efficient way to enumerate cells, including nucleated white cells and red cells, in body fluids. However, these automated cell counters have limitations in differentiating cells in body fluids. For this reason, cytocentrifugation, or cytospin, should be performed on every body fluid soon after the fluid is received to optimally preserve morphology. A cytospin slide is then held in reserve for possible optical microscopy. A separate cytospin should be performed if cytological examination is ordered.

Automated blood cell counters differ in their performance characteristics, so there is no one-size-fits-all set of rules regarding when optical microscopy should be performed. The majority of instruments are validated by the manufacturer for precision, accuracy, sensitivity, specificity, reference range, linearity, limits of detection, carryover, and analytical measurement range. Each laboratory should validate these performance characteristics according to its guidelines of acceptability.^1,2

Optical microscopy examination of cytospin preparations may be performed in specific situations. Each laboratory sets the rules for these examinations in conjunction with the laboratory medical director. The rules set by the laboratory should apply to red blood cell, white blood cell, and complete blood counts below the limits of detection, abnormal white blood cell scattergram, immature white blood cells, blast flags, cell agglutination/clusters flags, and increased high fluorescent cells in analyzers with a body fluid mode.³ White blood cell counts below the detection limit generally do not need a differential count. Descriptive comments may be used with any optical microscopy examination.

1. Clinical and Laboratory Standards Institute. H56-A: Body Fluid Analysis for Cellular Composition; Approved Guideline. CLSI; 2006.
2. Bourner G, De la Salle B, George T, et al. ICSH guidelines for the verification and performance of automated cell counters for body fluids. Int J Lab Hematol. 2014;36(6):598–612.
3. Buoro S, Appassiti Esposito S, Vavassori M, et al. Reflex testing rules for cell count and differentiation of nucleated elements in pleural and ascitic fluids on Sysmex XE-5000. J Lab Autom. 2016;21(2):297–304.

 

Roberta Zimmerman, MD
Clinical Laboratory Director
Northern Pathology Services, Grand Rapids, Minn.
Member, CAP Hematology/Clinical Microscopy Committee

Q. We treat all elevated troponins as critical values that necessitate a phone call to the ordering physician and documentation on the patient’s chart. Is this necessary? How does it affect patient treatment?

A. CLIA regulations require that a laboratory not only maintains a list of panic/alert/critical values in its written procedures but also that the ordering individual be alerted immediately to a finding of a critical value. However, CLIA does not indicate which tests and associated values should be considered to have imminently life-threatening or panic values. Developing and maintaining a critical value notification list should be a collaborative partnership between the laboratory’s medical leadership and clinical subject matter experts associated with the particular test—for example, cardiology with respect to troponin and critical care with respect to blood gas parameters.

Review of lists of critical tests and values and personal communications shows that troponin, as a critical value, does not appear often or consistently. Why that occurs is subject to interpretation, but it may be due to lack of harmonization between troponin assays or inter-institutional variability in the definition of critical value.

We cannot comment on whether or not your policy affects patient treatment at your institution. We suggest continuing the conversation with your cardiologists to clarify what they want that the laboratory can provide in a practicable and consistent manner.