System for detecting infection in synovial fluid

1. A method of evaluating joint pain in a human subject, comprising:

obtaining synovial fluid from a painful prosthetic joint in the subject;

contacting the synovial fluid with a reagent configured to specifically detect the expression level of a protein selected from the group consisting of neutrophil elastase 2 (ELA-2), bactericidal/permeability-increasing protein (BPI), neutrophil gelatinase-associated lipocalin/lipocalin 2 (NGAL), resistin, thrombospondin, lactoferrin, alpha-2 macroglobulin (α2M), or interferon gamma-induced protein 10 (IP-10);

evaluating the expression level of the protein in the synovial fluid, including comparing the expression level to a predetermined human expression level of the protein; and

treating the subject for septic inflammation of the prosthetic joint with an antibiotic when the expression level equals or exceeds the predetermined human expression level or treating the subject for aseptic inflammation with an antibiotic when the expression level is less than the predetermined human expression level.

2. The method according to claim 1 , further comprising contacting the synovial fluid with a reagent configured to specifically detect the expression of c-reactive protein (CRP), tumor necrosis factor-α, (TNFα), vascular endothelial growth factor (VEGF), fibroblast growth factor 2 (FGF2), skin-derived antileukoproteinase (SKALP), granulocyte-colony stimulating factor (G-CSF), interleukin-1α (IL-1α), interleukin-1β (IL-1β), interleukin-6 (IL-6), interleukin-8 (IL-8), interleukin-10 (IL-10), or interleukin-17 (IL-17).

3. The method according to claim 1 , wherein the predetermined human expression level is 400 ng/ml ELA-2.

4. The method according to claim 1 , wherein the predetermined human expression level is 800 ng/ml NGAL.

5. The method according to claim 1 , wherein the predetermined human expression level is 30 ng/ml resistin.

6. The method according to claim 1 , wherein the predetermined human expression level is 100 ng/ml thrombospondin.

7. The method according to claim 1 , wherein the predetermined human expression level is 900 ng/ml lactoferrin.

8. The method according to claim 1 , wherein the predetermined human expression level is 65 pg/ml α-2M.

9. The method according to claim 1 , wherein the predetermined human expression level is 3,000 pg/ml IP-10.

10. The method according to claim 1 , wherein the predetermined human expression level is derived from a receiver operating characteristic curve analysis.

11. The method according to claim 1 , further comprising treating the subject with an anti-bacterial agent when the synovial fluid comprises:

at least 8,000 ng/ml c-reactive protein (CRP);

at least 46 pg/ml tumor necrosis factor-α (TNFα);

at least 1,900 pg/ml vascular endothelial growth factor (VEGF);

at least fibroblast growth factor 2 (FGF2);

at least 1,500 pg/ml skin-derived antileukoproteinase (SKALP);

at least 60 pg/ml granulocyte-colony stimulating factor (G-CSF);

at least 15 pg/ml interleukin-1β (IL-1β);

at least 1,600 pg/ml interleukin-6 (IL-6);

at least 6,500 pg/ml interleukin-8 (IL-8);

at least 10 pg/ml interleukin-10 (IL-10); or

at least 7.2 pg/ml interleukin-17 (IL-17).

12. A method of evaluating a synovial fluid sample from a human subject, comprising:

determining a level of a first biomarker in a synovial fluid sample obtained from the subject, wherein the biomarker is selected from neutrophil elastase 2 (ELA-2), bactericidal/permeability-increasing protein (BPI), neutrophil gelatinase-associated lipocalin/lipocalin 2 (NGAL), resistin, thrombospondin, lactoferrin, alpha-2 macroglobulin (α2M), and interferon gamma-induced protein 10 (IP-10); and

comparing the first biomarker level to a first biomarker cut-off value derived from a receiver operating characteristic (ROC) curve analysis;

wherein the subject is treated for joint infection with an antibiotic when the first biomarker level is equal to or greater than the first biomarker cut-off value and the subject is treated for aseptic inflammation with an antibiotic when the first biomarker level is less than the first biomarker cut-off value.

13. The method according to claim 12 , wherein the ROC analysis includes samples obtained from prosthetic joints.

14. The method according to claim 12 , further comprising determining that the synovial fluid sample comprises a second biomarker that is specific to synovial fluid.

15. The method according to claim 14 , wherein the second biomarker comprises hyaluronic acid, mucopolysaccharide, glucosamine, chondroitin sulfate, cartilage oligomeric matrix protein, lumican, lubricin, or a combination thereof.

16. A method of evaluating a synovial fluid sample from a human subject, comprising:

obtaining a first plurality of synovial fluid samples from individuals confirmed to have septic joint inflammation and a obtaining a second plurality of synovial fluid samples from individuals confirmed to have aseptic joint inflammation;

determining the protein expression level of a biomarker selected from neutrophil elastase 2 (ELA-2), bactericidal/permeability-increasing protein (BPI), neutrophil gelatinase-associated lipocalin/lipocalin 2 (NGAL), resistin, thrombospondin, lactoferrin, alpha-2 macroglobulin (α2M), and interferon gamma-induced protein 10 (IP-10) in each one of the first plurality and the second plurality of synovial fluid samples;

performing a receiver operating characteristic (ROC) curve analysis of the area under the curve (AUC) for the biomarker expression levels;

selecting a biomarker cut-off value based on the ROC analysis;

determining a biomarker protein level in a synovial fluid sample obtained from the subject;

comparing the sample biomarker protein level to the biomarker cut-off value; and

indicating that the subject has a joint infection when the sample biomarker protein level is equal to or greater than the biomarker cut-off value and indicating that the subject has aseptic inflammation when the sample biomarker protein level is less than the cut-off value;

wherein the subject is treated for septic inflammation with an antibiotic when the biomarker level is equal to or greater than the biomarker cut-off value and the subject is treated for aseptic inflammation with an antibiotic when the biomarker level is less than the biomarker cut-off value.

17. The method according to claim 16 , wherein the first plurality of synovial fluid samples includes samples obtained from prosthetic joints.

18. The method according to claim 16 , wherein the second plurality of synovial fluid samples includes samples obtained from individuals confirmed to have gout, pseudo-gout, osteoarthritis, or metal-on-metal inflammation.

19. The method according to claim 16 , wherein the biomarker AUC is at least 0.9, the biomarker cut-off value has a sensitivity of least 90%, or the biomarker cut-off value has a specificity of at least 90%.