Laboratory Rounds Is this a Septic Joint?
Download
Report
Transcript Laboratory Rounds Is this a Septic Joint?
Laboratory Rounds
Is this a Septic Joint?
Mark Boyko, R3 EM
Case
53 yo female comes in with 2 day history
of increasing R knee pain, now giving her
a limp. Does not recall injuring it
That knee is always ‘a little sore’ from
running injuries years ago
Case
PMHx:
HTN
GERD
Smoker
Gout (toes, L ankle) – hasn’t had a flare in years
Meds
Allopurinol
Ramipril
Ranitidine
Case
Phx
No fever, normal vitals
Knee looks swollen, no
cellultis
Joint warm, ROM is
painful but patient can
do it
Labs
Serum WBC 14
ESR 32
CRP 17
Uric Acid 400
Synovial Fluid
WBC 36 x109/L, PMN’s 65%
Low glucose
Negative for crystals
Labs
Gram Stain
Negative
What do you want to do??
Overview
Value of serum labs
Value of synovial fluid analysis
Gram’s Stain & Cultures
Prosethetic Joints
Course of Action for Dry Taps
Review – The Swollen Joint
Non-inflammatory
Trauma
OA
Inflammatory
RA
Crystal arthropathies
Seronegative arthropathies
Septic joint
Why is this Important?
Joint destruction can occur within 2-3 days
if untreated infection
Patients can become systemically septic
from a joint infection rather easily
We need to make decisions before
cultures come back
We Love Prediction Tools
Can
anything help us rule this
out??
Serum Labs
Serum WBC
>10 x 109/L sensitivity of 50% for infection
LR 1.4
Many sterile but inflammatory joints give
elevated serum WBC
Bottom Line: Not sensitive
Serum Labs
Serum ESR
‘Elevation’ in most studies >30 mm/h
Sensitive but not specific
LR 1.3
Bottom Line: Only useful to track
resolution of the infection over time
Serum Labs
Serum CRP
‘Elevated’ in most studies >100 mg/L
Sensitivity 75%, poor specificity
LR 1.6
Bottom Line: Although CRP shows promise,
there is insufficient evidence for its sensitivity to
be high enough to rule out septic arthritis.
-Best Bets 2008
Synovial Fluid
What’s Normal?
Normal knee has avg 4cc synovial fluid
Normal synovial WBC <0.2x109/L
Glucose same as plasma
Uric Acid same as plasma
Protein <25% of plasma
Synovial Fluid
Normal – amber, transparent
Synovial Fluid
Inflammatory Cells - opaque
Synovial Fluid
Hemarthrosis
Hemarthrosis
Trauma #1 cause
Anticoagulation therapy
Hemophilia
Synovioma
Rarely, infection and hemarthrosis coexist. If concerned, send for culture.
Synovial Fluid
Findings
Normal
Non-Inflamm Inflammatory Septic
Colour
Clear
Yellow
Yellow
Yellow
Clarity
Transparent
Transparent
Opaque
Opaque
WBC (x109/L) <0.2
0.2 - 2
2 - 150
20 - 200
PMN’s
<25%
>50%
>75%
<25%
Synovial Fluid
Glucose and Protein
Synovial / Serum Glucose <0.5-0.75, low
sensitivity
Synovial Glucose <1.5 mmol/L sensitivity 38-64%
Synovial Protein >25% of plasma, low sensitivity
Bottom Line: Glucose and Protein levels have
no role in the work up of a septic joint
Synovial Fluid
LDH
Lactic Acid
>250 U/L was 100% sensitive in retrospective study
on 8 confirmed cases, prospectively was not as
strong
90-97% NPV, but low powered studies
Bottom Line: Insufficient data to date
Synovial Fluid
Tumour Necrosis Factor – α
Jeng et al, Am J Emerg Med 1997
Prospective, n=75
Synovial TNF-α >36.2 pg/mL sens 95%, spec
50% for bacterial infection
Bottom Line: Needs more study before
routine order
Synovial Fluid
WBC
<25
LR 0.32
>25
LR 2.9
>50
LR 7.7
>100
LR 28.0
Margeretten et al, JAMA 2007
Synovial Fluid
30% of immunocompetent people with
culture confirmed septic joint have
synovial WBC <50
- McGillicuddy et al, Am J Emerg Med. 2007
50% of immunocompromised people
with culture confirmed joint infection had
WBC <28
-McCutchan et al, Clin Orthop Relat Res 1990
Synovial Fluid
PMN’s
<90%
LR 0.34
>90%
LR 3.4
Margeretten et al, JAMA 2007
Synovial Fluid
WBC Bottom Line
Cut-off of 50 x109 /L too insensitive rule-out
infection
Use in clinical context
The diagnostic cut-off that maximized the
sensitivity / specificity was a synovial WBC
count of 17.5 x109/L (Sens 83%, Spec 67%)
- Li et al, Emerg Med J 2007
Synovial Fluid
Eosinophilia
Parasitic infection
Allergy
Fungal
Neoplasm
Lyme disease
Combined Value?
Li et al, Emerg Med J 2007
Retrospective chart review 156 patients
Combined Sensitivity 100% if:
Serum WBC <11
Serum ESR <20
Synovial WBC <50
Bottom Line: Not powered enough, not
prospectively validated, cannot use to rule out
septic joint
Synovial Fluid
Crystals
Gout - Monosodium Urate, 90% sensitive, LR 14
Pseudogout – PPDC, 80% sensitive, LR 2.6
Cholesterol crystals – seen in chronic
inflammatory conditions
Crystals & Infection
Crystals do not rule out infection!
Retrospective study n=265 patients with
crystals, 1.5% had septic joint
-Shah et al, J of Emerg Med 2007
Literature ranges from 1-20% of infectious
joints co-exist with crystals
Microbio Review
ALL AGES: #1 cause still Staph Aureus
<30, sexually active: Neisseria Gonorrhea
Elderly: Gram Negatives
Prosthetics: Careful of Pseudomonas
Gram’s Stain
Guides your antibiotic therapy while awaiting
cultures
Need roughly 3-5cc for stain & culture
Only 65% sensitive for non-gonococcal
infections
Only 25% sensitive for gonococcal infections
Bottom Line: A negative Gram stain means
nothing. A positive Gram stain means you
should start treatment.
Cultures
‘Gold standard’ ?
Gonococcus difficult to culture
Negative 50% of the time
Requires chocolate agar
Non-gonococcus will culture 90% of time
If you only have enough fluid for one test, this is
what you do
Blood cultures reveal pathogen 25-50% of the
time
Gonococcal Arthritis
Synovial WBC often <50
Gram stain Positive only 25% of the time
Culture Positive only 50% of the time
If you suspect it, culture at 3 mucosal sites (pharynx,
genitals, anus) will increase your chance of positive
culture to 80%
Generally less destructive to the joint versus other
pathogens
Gram Stain Positive, Culture
Negative
In reality, this is retrospective
Go with your Gram Stain treat these
patients while awaiting cultures
How does this happen?
Antibiotics already on board
Organism difficult to culture
Was infected, now clearing
Prosthetic Joints
<3mos since surgery
likely Staph Epiderm
>3mos since surgery
Staph, Strep, Gram Neg
Should always call Ortho
before tapping these in ER
Prosthetic Joints
Trampuz et al, Amer J of Med 2004
Prospective, n=133, 34 had septic joint
Synovial WBC >1.7 x109/L , sens 94% spec 88%
Synovial PMN’s >65%, sens 97% spec 98%
Mason et al, J of Arthroplasty 2003
Retrospective n=86 knees
Ideal sensitivity 98% for synovial WBC 2.5 x109/L and
PMN’s 60%
What About Those Dry Taps?
Dry Tap?
Makes a septic joint unlikely usually a large
enough effusion for tap, but never been
validated
Options
U/S guided in the department
Consult Ortho
Fluoroscopy guided
BOTTOM LINE: You need a sample of that fluid
if you are worried about infection
Hot Joint, No Organism
Fastidious organism
Antibiotics begun before cultures sent
Wrong Diagnosis
Help increase your yield?
Use blood culture bottles for synovial fluid
(aerobic and anaerobic)
- Joint, Bone, Spine 2006
Relevance to Pediatrics?
No good studies specifically on synovial
fluid analysis in the pediatric population
Most use numbers from adult data
How Many Use Kocher’s Criteria?
Kocher et al, J of Bone Joint Surg 2004
TAKE HOME MESSAGE
Cannot rely on serum values to rule out
septic joint
If you believe there’s an effusion, get that
fluid somehow
Unfortunately, nothing has a strong NPV
TAKE HOME MESSAGE
Synovial fluid: WBC & PMN is helpful
WBC <18 is low risk but not zero
WBC >50 is high likelihood
PMN’S >90% is high likelihood
Glucose, Protein useless
TAKE HOME MESSAGE
‘Gold Standard’ is clinical suspicion of an
experienced physician, not laboratory tests
(Current Opinion Rheumatology 2008)
Prosthetic Joints
Lower WBC & PMN threshold
Don’t feel bad - 30% of the time reason for
effusion remains ‘unknown’
Thanks
Feel free to ask for any references