Good accuracy of the alpha-defensin lateral flow test for hip periprosthetic joint infection: A pilot study in a retrospective cohort of 52 patients

Table 1 Modified Musculoskeletal Infection Society criteria for periprosthetic joint infection definition[3]

Two or more positive periprosthetic cultures with phenotypically identical organisms, or

A sinus tract communicating with the joint, or

Having at least three of the following minor criteria:

Elevated serum C-reactive protein > 10 mg/L AND erythrocyte sedimentation rate > 30 mm/h;

Elevated synovial fluid white blood cell count 3.000 cells/μL OR ++ result on leukocyte esterase test strip;

Elevated synovial fluid polymorphonuclear neutrophil percentage (PMN%) > 80%;

Positive histological analysis of periprosthetic tissue;

A single positive culture.

Table 2 European Bone and Joint Infection Society criteria for periprosthetic joint infection definition. One or more criteria fulfilled means positive periprosthetic joint infection diagnosis[4]

Sinus tract OR purulence around the prosthesis;

Acute inflammation on histopathology of periprosthetic tissue;

Elevated synovial fluid white blood cell count of more than 2.000 cells/μL OR elevated synovial fluid polymorphonuclear neutrophil percentage (PMN%) > 70%;

Microbial growth in synovial fluid OR > 2 tissue samples (for highly virulent microorganisms already one positive sample confirms infection) OR sonication fluid (≥ 50 CFU/mL).

Table 3 New 2018 International Consensus Meeting scoring criteria for periprosthetic joint infectiondefinition[5]: Major criteria (at least one of the following)

Two positive cultures of the same organism	Infected
Sinus tract with evidence of communication to the joint or visualization of the prosthesis

Table 4 New 2018 International Consensus Meeting scoring criteria for periprosthetic joint infection definition[5]: Preoperative diagnosis

Preoperative score: Minor criteria	Score	Decision
Serum: Elevated CRP or D-Dimer	2	≥ 6: Infected
Serum: Elevated ESR	1
Synovial: Elevated synovial WBC count or LE	3	2-5: Possibly infected1
Synovial: Positive alpha-defensin	3
Synovial: Elevated synovial PMN (%)	2	0-1: Not infected
Synovial: Elevated synovial CRP	1

¹See table 5. CRP: C-reactive protein; ESR: Erythrocyte sedimentation rate; WBC: White blood cell; PMN: Polymorphonuclear neutrophil.

Table 5 New 2018 International Consensus Meeting scoring criteria for periprosthetic joint infection definition[5]: Intraoperatieve diagnosis

Inconclusive preoperative score1or dry tap	Score	Decision
Preoperative score	-	≥ 6: Infected; 4-5: Inconclusive; 0-3: Not infected
Positive histology	3
Positive purulence	3
Single positive culture	2

¹see Table 4.

Table 6 Demographics of the described cohort and the group of excluded patients (no alpha-defensin lateral flow test performed)

	Cohort	Excluded
Total (n)	52	31
Age [mean (SD), yr]	72 (9.2)	67.5 (9.5)
Gender (n)
Male	24	12
Female	28	19
Operated side (n)
Right	28	12
Left	24	19
Prosthesis (n)
Total hip arthroplasty	46	26
Hemi-arthroplasty	6	5
Articulation (n)
MoP	31	18
CoP	8	4
CoC	4	3
MoM	3	1
HA	6	5
Time to aspiration [Median (range), mo]	35 (3-266)	32.4 (3-191)

MoP: Metal on polyethylene; CoP: Ceramic on polyethylene; MoM: Metal on metal; HA: Hemiarthroplasty

Table 7 Characteristics of all patients with positive alpha-defensin lateral flow test and/or positive or inconclusive criteria

Case	Criteria	A	B	C	D	E	F	G	H	I	PJI?
	Art	Sinus tract	Visible purulence	CRP (mg/ L)	ESR (mm/h)	WBC count (cells/μL)	PMN%	Culture synovial fluid (nr of cultures)	Culture tissue (nr of cultures)	AD	MSIS (+/-; criteria)		EBJIS (+/-; criteria)		2018 ICM (+/-/i; criteria)		Revision surgery	1- or 2-stage
1	CoC	-	-	6.5	21.0	19100	91	neg (1)	neg (6)	+	-	E,F	+	E,F	+	E,F,I	Yes	2-stage
2	MoP	Yes	-	9.0	23.0	-	-	pos (2)	pos (8/9)	+	+	A,G,H	+	A,G,H	+	A,G,H,I	Yes	2-stage
3	MoP	-	-	8.5	29.0	3000	4	neg (2)	-	-	-		+	E	-		No	-
4	MoP	-	-	9.8	16.0	6200	77	neg (2)	pos (5/8)	+	+	E,H	+	E,F,H	+	E,H,I	Yes	2-stage
5	CoC	-	-	6.9	10.0	2300	-	neg (1)	-	-	-		+	E	-		No	-
6	MoP	-	-	12.0	26.0	10	-	neg (2)	pos (1/2)	-	-	C,H	-		i	C,H	Yes	1-stage
7	MoP	-	-	-	-	9350	-	neg (1)	-	-	-	E	+	E	-	E	No	-
8	HA	-	-	-	-	-	-	neg (1)	pos (1/6)	+	-	H	-		i	H,I	Yes	1-stage
9	MoP	-	-	144.0	64.0	37300	92	pos (1/2)	pos (2/6)	+	+	C,D,E,F,G,H	+	E,F,G,H	+	C,D,E,F,H,I	Yes	DAIR
10	MoP	-	-	61.0	72.0	7900	95	pos (1/1)	pos (9/9)	+	+	C,D,E,F,G,H	+	E,F,G,H	+	C,D,E,F,H,I	Yes	2-stage
11	MoP	-	-	71.0	55.0	35300	97	pos (2/2)	pos (7/7)	+	+	C,D,E,F,G,H	+	E,F,G,H	+	C,D,E,F,H,I	Yes	2-stage
12	HA	-	-	9.6	-	4900	81	-	-	+	-	E,F	+	E,F	+	E,F,I	No	-
13	MoM	-	Yes	195.0	-	264000	96	neg (2)	-	+	+	B,C,E,F	+	B,E,F	+	B,C,E,F,I	No	-
14	MoP	-	-	15.0	13.0	8000	-	neg (1)	neg (6)	+	-	C,E	+	E	+	C,E,I	Yes	2-stage
15	HA	-	-	1.0	9.0	4000	15	neg (2)	-	-	-	E	+	E	-	E	No	-
16	MoM	-	-	5.7	8.0	5170	52	neg (3)	-	+	-	E	+	E	+	E,I	No	-

Art: Articulation; CoC: Ceramic on ceramic; MoP: Metal on polyethylene; MoM: Metal on metal; HA: Hemiarthroplasty; CoP: Ceramic on polyethylene; CRP: C-reactive protein; ESR: Erythrocyte sedimentation rate; WBC: White blood cell; PMN%: Polymorphonuclear neutrophil percentage; PJI: Prosthetic joint infection; AD: Alpha-defensin test; MSIS: Musculoskeletal Infection Society; EBJIS: The European Bone and Joint Infection Society; i: Inconclusive; +: Positive; -: Negative.

Table 8 All cases of positive cultures in the described cohort

Case	Culture after aspiration (positive cultures/nr of total cultures)	Culture after revision (positive cultures/nr of total cultures)
2	Propionibacterium acnes (2/2)	Cutibacterium acnes (8/9)
	Staphylococcus aureus (1/2)
4	Negative (2/2)	Staphylococcus capitis (5/8)
		Staphyloccus hominis (1/8)
		Staphylococcus epidermidis (1/8)
		Propionibacterium acnes (1/8)
7	Negative (2/2)	Propionibacterium acnes (1/2)
8	Negative (1/1)	Staphylococcus capitis (1/6)
9	Staphylococcus aureus (1/2)	Staphylococcus aureus (2/6)
10	Pseudomonas aeruginosa (1/1)	Pseudomonas aeruginosa (9/9)
		Staphylococcus epidermidis (1/9)
13	Staphylococcus lugdunensis (2/2)	Staphylococcus lugdunensis (7/7)