Editor: Frederick L. Kiechle, MD, PhD
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Q. Learning material from the past CAP continuing education course “Analysis of Synovial Fluid: A Joint Effort” included commentary about collecting and evaluating synovial fluid: “Certain anticoagulants, such as oxalate, powdered EDTA and lithium heparin, should not be used since they have ingredients that mimic crystals and can cause false positives or complicate the evaluation.”
There seems to be conflicting information in the literature concerning specimen preservative for crystal analysis. For example, the CLSI document titled “H56-A: Body Fluid Analysis for Cellular Composition; Approved Guideline” states: “Some texts indicate that lithium heparin and EDTA should not be used as anticoagulants, because they produce crystalline material that can be confused with pathologic crystals. However, others have used lithium heparin and EDTA without difficulty.” The text is followed by a table, “Specimen Requirements for Synovial Fluid,” that lists heparin and EDTA as the anticoagulants of choice for cell count, differential, crystals, and inclusions. It seems, according to the CLSI, both anticoagulants are equally acceptable or unacceptable.
The CAP Hematology and Clinical Microscopy Resource Committee’s Color Atlas of Body Fluids states, “Inflammatory fluids may clot spontaneously and, if an anticoagulant is used, sodium heparin is the agent of choice as other commonly used anticoagulants may introduce artifacts complicating crystal categorization.”
The third edition of Body Fluids: Laboratory Examination of Amniotic, Cerebrospinal, Seminal, Serous and Synovial Fluids states something similar to the Color Atlas of Body Fluids : “For routine examination, the syringe used for removing the fluid should be moistened with an anticoagulant (approximately 25 units of sodium heparin per milliliter of synovial fluid). Oxalate, powdered ethylenediaminetetraacetic acid (EDTA), and lithium heparin should not be used because they can produce artifacts in the microscopic examination for crystals.”
One thing is certain: Oxalate is not acceptable. It is unclear, however, which preservative is recommended or if the recommendation is to not use a preservative. We follow the CSLI guideline and use lithium heparin for our crystal analysis. Should we use sodium heparin instead or no preservative at all? Is there a specific CAP recommendation that addresses crystal analysis preservative? If not, what does the CAP recommend?
A. Your quandary is certainly understandable, particularly in light of the sources you cite. While this issue can get confusing, keeping a few things in mind may help to clarify the appropriate approach for your laboratory.
First, a few specifics on the collection tubes. The references you cite recommend caution for oxalate, lithium heparin, and the powdered form of EDTA due to the risk that crystalline-like materials intrinsic to those types of collection tubes will be mistaken for clinically significant crystals during evaluation for crystals in synovial fluid. To my knowledge, the risk of false-positive crystal evaluation has not been reported for sodium heparin or liquid EDTA, and the references you cite seem consistent with that assertion, although the wording varies.
The CAP does not have a position regarding which anticoagulants are acceptable for synovial fluid crystal analysis. In this instance, applying the principles of best laboratory practice to the circumstances of your laboratory will yield the best results for patients. Given the risk of false-positives, if all other things are equal your lab may want to consider exploring sodium heparin or liquid EDTA as options for synovial fluid collection. However, other testing is often performed on synovial fluid, and those procedures may influence anticoagulant selection. Therefore, it may be acceptable to use an anticoagulant other than sodium heparin or liquid EDTA in certain circumstances. No matter which anticoagulant is used, the validation designed for the testing should incorporate the body fluid being tested and the specific collection tube(s) that will be used for clinical testing, and the validation data must demonstrate acceptable performance prior to implementing the test. If, for example, lithium heparin is preferred or required for some reason and the validation demonstrates acceptable concordance—that is, its use does not pose a risk of false-positive crystals and/or any anticoagulant-derived crystalline material can be readily distinguished from clinically significant crystals without error—its use may be acceptable.
It is important to note that CAP continuing education pieces are intended solely for educational purposes and should not be interpreted as CAP policy. Continuing education pieces on a range of topics are available at no charge to laboratories that use CAP proficiency testing kits. To see a list of available topics, visit CAP Learning (https://learn.cap.org). To access a specific continuing education piece, you will need your laboratory’s access code for the corresponding proficiency testing kit.
- Clinical and Laboratory Standards Institute. H56-A: Body Fluid Analysis for Cellular Composition; Approved Guideline; 2006.
- Galagan KA, Blomberg D, Cornbleet PJ, Glassy EF, eds. Color Atlas of Body Fluids: An Illustrated Field Guide Based on Proficiency Testing. Northfield, Ill.: CAP Press; 1993.
- Kjeldsberg CR, Knight JA. Body Fluids: Laboratory Examination of Amniotic, Cerebrospinal, Seminal, Serous and Synovial Fluids. Chicago: American Society of Clinical Pathologists Press; 1993.
- Ringsrud KM, Linné JJ. Urinalysis and Body Fluids: A Colortext and Atlas. St. Louis, Mo.: Mosby; 1995.
David S. Bosler, MD
Staff, Molecular Pathology, Hematopathology
Department of Laboratory Medicine
Robert J. Tomsich Pathology and
Laboratory Medicine Institute
Cleveland Clinic
Chair, CAP Point of Care
Testing Committee
In upcoming issues, we will reprint a few coagulation-related questions and answers in a “Best of Q&A” series. They date back to 2014 but all have been reviewed for their timeliness and relevance today. The following question and answer were published in May 2017.
Q. What is the next step in resolving platelet clumping when it occurs in a citrate tube also?
A. Pseudothrombocytopenia can occur in a variety of conditions and has been associated with EDTA-dependent agglutinins, other cold agglutinins, multiple myeloma, infections, anticardiolipin antibodies, high immunoglobulin levels, and abciximab therapy. EDTA-associated pseudothrombocytopenia is the most common cause. Evaluation of pseudothrombocytopenia includes evaluation of a peripheral blood smear for evidence of platelet clumping or platelet binding to neutrophils (platelet satellitism). Alternative anticoagulants can be tried, including citrate and heparin. If platelet clumping still occurs, blood can be collected directly from a fingerstick into a diluent for manual counting and for direct preparation of smears.
Nakashima MO, Kottke-Marchant K. Platelet testing. In: Kottke-Marchant K, ed. An Algorithmic Approach to Hemostasis Testing, 2nd ed. Northfield, Ill.: CAP Press; 2016:101.
Wayne L. Chandler, MD
Division Chief, Laboratory Medicine
Department of Laboratories
Seattle Children’s Hospital
Member of the CAP Coagulation Resource Committee at time of original publication