Page 139 - Canine Lameness

111

9

Joint Fluid Analysis and Collection Considerations

Adam Harris and Kelly Santangelo

Department of Microbiology, Immunology, and Pathology, College of Veterinary Medicine and Biomedical Sciences,
Colorado State University, Fort Collins, CO, USA

9.1 Introduction

Synovial fluid is a viscous substance produced and contained within diarthrodial (i.e. freely mov-
able) joints. Synovial fluid analysis is a valuable tool used to diagnose and monitor primary and
secondary articular joint disorders. Information gained from cytological evaluation of synovial
fluid is most helpful when combined with patient history, physical exam, imaging findings, and
other laboratory data, such as bacterial culture and serology. For procedural details of arthrocente-
sis, please refer to Chapter 7.

9.2 Sample Submission and Prioritization of Diagnostic Tests

Pre‐analytical errors involving sample collection and specimen handling can vastly alter results. In
general, synovial fluid should be shipped at 4 °C and delivered within 24 hours. Fresh smears made
at the time of collection are best for maintaining cellular morphology. If cytology is a primary out-
come but adequate smears cannot be made by the referring clinician at the time of sample aspira-
tion, smears should be made at the clinical pathology laboratory from samples stored in
ethylenediaminetetraacetic acid (EDTA) tubes. Heparinized samples will not adequately preserve
mammalian cell architecture.
Between 0.01 and 1 ml of synovial fluid may be aspirated from non‐pathologic joints of dogs,
with larger joints normally containing more fluid for sampling. As little as a single drop of joint
fluid can be considered within normal limits, particularly in small‐breed dogs. Joint pathology
often increases joint fluid volume and clinicians should be suspicious of pathology in cases where
the aspirated volume is >1 ml (Clements 2006). Given that aspiration of synovial fluid can yield
variable amounts, allocation of the available sample for priority of diagnostic tests is important
(Figure 9.1) and should be made considering the most likely differential diagnoses. If adequate
joint fluid is retrieved, submission of the sample as direct smears, in EDTA tubes (purple or laven-
der tubes), sterile no‐additive tubes (red top glass tubes), and blood culture flasks (if culture is
indicated) are recommended.

Canine Lameness, First Edition. Edited by Felix Michael Duerr.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/duerr/lameness