The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 92, Issue 5

Letters to the Editor | May 01, 2010

Cell Count and Differential of Aspirated Fluid in the Diagnosis of Infection at the Site of Total Knee Arthroplasty

Peter G. Elsissy, MD; W. Tait Stevens, MD; Brandon Ellsworth, MD; Nakul Karkare, MD

Disclosure: The authors did not receive any outside funding or grants in support of their research for or preparation of this work. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity.

Corresponding author: Peter G. Elsissy, MD, Loma Linda University Medical Center, 11406 Loma Linda Drive, Suite 218, Loma Linda, CA 92354, e-mail: peter.elsissy@gmail.com

J Bone Joint Surg Am, 2010 May 01;92(5):1312-1312

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Editor's Note:

Figures in this Article

Introduction

Introduction | References

Editor's Note:

As the following Letters to the Editor indicate, a concern was raised that an incorrect unit was utilized to express the white blood cell count in a joint aspirate that should be used for the diagnosis of an infection in two articles previously published in the Journal of Arthroplasty. The editorial staff of The Journal of Arthroplasty has investigated this issue and has published an erratum in the December 2009 issue of that journal (J Arthroplasty. 2009;24:1293) stating that the units were incorrect.

To The Editor:

In their recent study, "Cell Count and Differential of Aspirated Fluid in the Diagnosis of Infection at the Site of Total Knee Arthroplasty" (2008;90:1637-43), Ghanem et al. reported cell counts in terms of cells/10^-3cm³ (equivalent to cells/µL). However, when citing two articles, one by Kersey et al.¹ and one by Mason et al.², Ghanem et al. stated that the authors of those articles reported cell count values as cells/10^-3cm³ when, in fact, each used cells/mL to report their values. Elsewhere in the literature, some authors have reported values in terms of cells/mL while others have used cells/µL. This 1000-fold error in units has introduced confusion into the interpretation of this important body of literature.

The frequently quoted guidelines from the American College of Rheumatology (ACR) for cutoff values suggestive of infection in natural joints (joints without implants) use cells/µL (50,000 leukocytes/µL and 75% neutrophils)^3-7. Therefore, one would assume that researchers investigating cutoff values in the setting of an infection at the site of a prosthetic joint should use these same units.

On the basis of our review of the literature (Table I), we feel that authors who reported cell counts in terms of cells/mL may have intended to use cells/µL (as established by the ACR guidelines). If the data are reviewed exactly as each author has reported it, the recommended cutoff values range from as little as 2, to as high as 1760, cells/µL^1,2,8-12. However, if our assumption that all authors who used cells/mL to report values actually intended to use cells/µL is true, then the data become much more uniform, with recommended cutoff values falling between 500 and 2500 cells/µL, a much more clinically useful range.

Despite the disparities in cell count analysis, there is fairly uniform agreement that differentials showing greater than 60% to 75% neutrophils are highly suggestive of infection^1,2,8-12.

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TABLE I Review of Recommended Cutoff Values and Units for Diagnosis of Infection

Study	Study Design/Number of Patients	Units Used	Units Referenced	Recommended Cutoff Values*	Discussion Points
Ghanem et al., J Bone Joint Surg Am 2008	Multicenter retrospective review/429 pts	Cells/10^-3cm³ (µL)	Incorrectly expressed Kersey et al. and Mason et al. data in cells/µL when both sets of authors used cells/mL	1100 cells/µL and 64% PMN	Correctly cited ACR guidelines for native knees with cutoff at 50,000 cells/µL
Parvizi et al.⁸, J Bone Joint Surg Am 2006	Single-center retrospective review/168 pts (145 total knee arthroplasties, 23 total hip arthroplasties)	Cells/µL	Accurately expressed Spangehl et al. and Trampuz et al. data in cells/µL	1760 cells/µL and 73% PMN
Bauer et al.⁹, J Bone Joint Surg Am 2006	Current Concepts Review	Cells/µL	Expressed Spangehl et al., Kersey et al., Mason et al., and Trampuz et al. data in proper units used by original authors	500 cells/µL	Commented on inconsistency in units used by various authors and suggested that units may be erroneous
Trampuz et al.¹⁰, Am J Med 2004	Prospective study/133 pts	Cells/µL	Incorrectly expressed Kersey et al. and Mason et al. data in cells/µL when both sets of authors used cells/mL	1700 cells/µL and 65% PMN
Mason et al.², J Arthroplasty 2003	Retrospective review/86 pts	Cells/mL in body text; cells/mm³ (µL) in abstract	Incorrectly expressed multiple authors’ data in cells/mL when original data were in cells/µL	2500 cells/mL (2.5 cells/µL) and 60% PMN	1000-fold error in units
Kersey et al.¹, J Arthroplasty 2000	Prospective study/79 knees aspirated prior to revision for aseptic failure	Cells/mL	One case had infection leading to discussion of cutoff values	<2000 cells/mL (2 cells/µL) and <50% PMN had 98% NPV for absence of infection	Frequently misquoted, along with Mason et al. data, as cells/µL
Spangehl et al.¹¹, J Bone Joint Surg Am 1999	Prospective study/183 pts	Cells/µL	Analyzed aspirates using correct ACR recommended cutoff for knees without implants	Used ACR criteria of 50,000 cells/µL and 75% PMN for septic arthritis	ACR criteria for predicting infection in knees without implants had poor sensitivity (36%) for predicting infection at site of total knee arthroplasty

*PMN = polymorphonuclear leukocytes, and NPV = negative predictive value.

TABLE I Review of Recommended Cutoff Values and Units for Diagnosis of Infection

Study	Study Design/Number of Patients	Units Used	Units Referenced	Recommended Cutoff Values*	Discussion Points
Ghanem et al., J Bone Joint Surg Am 2008	Multicenter retrospective review/429 pts	Cells/10^-3cm³ (µL)	Incorrectly expressed Kersey et al. and Mason et al. data in cells/µL when both sets of authors used cells/mL	1100 cells/µL and 64% PMN	Correctly cited ACR guidelines for native knees with cutoff at 50,000 cells/µL
Parvizi et al.⁸, J Bone Joint Surg Am 2006	Single-center retrospective review/168 pts (145 total knee arthroplasties, 23 total hip arthroplasties)	Cells/µL	Accurately expressed Spangehl et al. and Trampuz et al. data in cells/µL	1760 cells/µL and 73% PMN
Bauer et al.⁹, J Bone Joint Surg Am 2006	Current Concepts Review	Cells/µL	Expressed Spangehl et al., Kersey et al., Mason et al., and Trampuz et al. data in proper units used by original authors	500 cells/µL	Commented on inconsistency in units used by various authors and suggested that units may be erroneous
Trampuz et al.¹⁰, Am J Med 2004	Prospective study/133 pts	Cells/µL	Incorrectly expressed Kersey et al. and Mason et al. data in cells/µL when both sets of authors used cells/mL	1700 cells/µL and 65% PMN
Mason et al.², J Arthroplasty 2003	Retrospective review/86 pts	Cells/mL in body text; cells/mm³ (µL) in abstract	Incorrectly expressed multiple authors’ data in cells/mL when original data were in cells/µL	2500 cells/mL (2.5 cells/µL) and 60% PMN	1000-fold error in units
Kersey et al.¹, J Arthroplasty 2000	Prospective study/79 knees aspirated prior to revision for aseptic failure	Cells/mL	One case had infection leading to discussion of cutoff values	<2000 cells/mL (2 cells/µL) and <50% PMN had 98% NPV for absence of infection	Frequently misquoted, along with Mason et al. data, as cells/µL
Spangehl et al.¹¹, J Bone Joint Surg Am 1999	Prospective study/183 pts	Cells/µL	Analyzed aspirates using correct ACR recommended cutoff for knees without implants	Used ACR criteria of 50,000 cells/µL and 75% PMN for septic arthritis	ACR criteria for predicting infection in knees without implants had poor sensitivity (36%) for predicting infection at site of total knee arthroplasty

*PMN = polymorphonuclear leukocytes, and NPV = negative predictive value.

References

Introduction | References

Kersey R; Benjamin J; Marson B. White blood cell counts and differential in synovial fluid of aseptically failed total knee arthroplasty. J Arthroplasty. 2000;15:301-4.[PubMed][CrossRef]

Mason JB; Fehring TK; Odum SM; Griffin WL; Nussman DS. The value of white blood cell counts before revision total knee arthroplasty. J Arthroplasty. 2003;18:1038-43.[PubMed][CrossRef]

Hasselbacher P. Arthrocentesis synovial fluid and synovial biopsy. In: Klippel JH; Weyand CM; Wortmann R, editors. Primer on the rheumatic diseases. 11th ed. Atlanta: Arthritis Foundation; 1997. p98-104.

Kortekangas P; Aro HT; Tuominen J; Toivanen A. Synovial fluid leukocytosis in bacterial arthritis vs. reactive arthritis and rheumatoid arthritis in the adult knee. Scand J Rheumatol. 1992;21:283-88.[PubMed][CrossRef]

Krey PR; Bailen DA. Synovial fluid leukocytosis. A study of extremes. Am J Med. 1979;67:436-42.[PubMed][CrossRef]

Kunnamo I; Pelkonen P. Routine analysis of synovial fluid cells is of value in the differential diagnosis of arthritis in children. J Rheumatol. 1986;13:1076-80.[PubMed]

McCarty DJ. Synovial fluid. In: Koopman WJ, editor. Arthritis and allied conditions: a textbook of rheumatology. 13th ed. Baltimore: Williams and Wilkins; 1997. p81-102.

Parvizi J; Ghanem E; Menashe S; Barrack RL; Bauer TW. Periprosthetic infection: what are the diagnostic challenges?J Bone Joint Surg Am. 2006;88 Suppl 4:138-47.[PubMed][CrossRef]

Bauer TW; Parvizi J; Kobayashi N; Krebs V. Diagnosis of periprosthetic infection. J Bone Joint Surg Am. 2006;88:869-82.[PubMed][CrossRef]

Trampuz A; Hanssen AD; Osmon DR; Mandrekar J; Steckelberg JM; Patel R. Synovial fluid leukocyte count and differential for the diagnosis of prosthetic knee infection. Am J Med. 2004;117:556-62.[PubMed] [CrossRef]

Spangehl MJ; Masri BA; O'Connell JX; Duncan CP. Prospective analysis of preoperative and intraoperative investigations for the diagnosis of infection at the sites of two hundred and two revision total hip arthroplasties. J Bone Joint Surg Am. 1999;81:672-83.[PubMed]

Leone JM; Hanssen AD. Management of infection at the site of a total knee arthroplasty. Instr Course Lect. 2006;55:449-61.[PubMed]

Topics

cell count ; pulmonary aspiration ; knee replacement arthroplasty ; infectious disease diagnosis

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Peter G. Elsissy, W. Tait Stevens, Brandon Ellsworth, Nakul Karkare; Cell Count and Differential of Aspirated Fluid in the Diagnosis of Infection at the Site of Total Knee Arthroplasty. The Journal of Bone & Joint Surgery. 2010 May;92(5):1312-1312.

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