11/13/24, 7\:32 PM Guide | Joint fluid interpretation

Joint

Table of contents

Introduction

This guide provides a structured approach to joint
disease processes. Reference ranges vary between labs, so always consult your local medical school or hospital guidelines.

Normal joint

Colour\: colourless
Clarity\: transparent
Viscosity\: normal
WBC\: \< 200 cells/mm
3
Neutrophils (% of total WCC)\: \<25 %
Gram stain\: negative
Crystals\: negative

Overview

This table summarises the typical
Joint

Non-in

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Aetiology

Causes of non-in
Osteoarthritis
Trauma

Clinical features

Typical clinical features of non-in
Localised joint pain
Gradual onset of symptoms
Pain on movement, worse at the end of the day
Crepitus

Joint

Typical joint
Colour\: straw-like
Clarity\: translucent
Viscosity\: increased
WBC\: 200 - 2000 cells/mm
3
Neutrophils\: \<25 %
Gram stain\: negative
Crystals\: negative

Further investigations

Further investigations for suspected non-in
Blood tests (FBC, CRP)\: typically normal in non-in
X-ray of the a
MRI of the a

In

Aetiology

Causes of in
Rheumatoid arthritis
Reactive arthritis
Psoriatic arthritis
Acute gout or pseudogout

Clinical features

Rheumatoid arthritis
Typical clinical features of in
Symmetrical swollen, warm, erythematous and painful joints
Usually, the small joints of the hands and feet are a
Morning sti
May be associated with systemic features (e.g. fever, weight loss)
Psoriatic arthritis
Typical clinical features of in
A
Small joints of the hand and wrist are commonly a
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Typically asymmetrical in presentation
Associated changes to the nails, such as onycholysis and hyperkeratosis
Acute gout
Typical clinical features of in
A single hot, swollen and tender joint (most commonly the metatarsophalangeal joint at the base of the big toe).
Pseudogout
Typical clinical features of in
A single hot, swollen and tender joint (most commonly the knee joint)

Joint

Typical joint
Colour\: yellow
Clarity\: cloudy
Viscosity\: decreased
WBC\: 2000–50,000 cells/mm
3
Neutrophils\: >50 %
Gram stain\: negative
Crystals\: positive
Gout - needle negative birefringent crystals
Pseudogout - rhomboid positively birefringent crystals

Further investigations

Further investigations for suspected in
Full blood count
CRP
ESR
Urate (raised in gout)
Antibodies (e.g. anti-CCP, rheumatoid factor - both typically positive in rheumatoid arthritis)
X-ray of the joint\: may reveal joint erosions/destruction

Septic joint e

Aetiology

Causes of septic joint e
Staphylococcus aureus
Streptococci
Neisseria gonorrhoeae (young sexually active adults)
Escherichia coli (elderly, intravenous drug users)

Clinical features

Typical clinical features of septic joint e
A single painful, swollen and warm joint
Associated fever and other systemic features (e.g. tachycardia, hypotension)

Joint

Typical joint
Colour\: yellow/green
Clarity\: cloudy/opaque
Viscosity\: decreased
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WBC\: >50 000 cells/mm
3
Neutrophils\: >75 %
Gram stain\: often positive
Crystals\: negative

Further investigations

Further investigations for suspected septic joint e
Full blood count\: WCC is typically raised
CRP\: typically raised
Blood cultures\: may identify the causative organism
Joint
X-ray of the joint\: may reveal joint destruction

Haemorrhagic joint e

Aetiology

Causes of haemorrhagic joint e
Trauma
Tumours
Bleeding disorders

Clinical features

Typical clinical features of a haemorrhagic joint e
A painful, swollen and warm single joint
Restricted range of movement in the a
Excessive bruising surrounding the a

Joint

Typical joint
Colour\: red/xanthochromic
Clarity\: bloody
Viscosity\: variable
WBC\: 200-2000 mm³
Neutrophils\: 50-75%
Gram stain\: negative
Crystals\: negative

Further investigations

Further investigations for suspected haemorrhagic joint e
Full blood count\: haemoglobin may be reduced if the bleeding was signi
Coagulation studies\: may reveal impaired coagulation
X-ray of the a

Worked examples

Case 1

A 23-year-old female presents with a swollen and warm knee joint that is very painful on
mentions she has been su
partners and uses condoms inconsistently. Her knee joint is aspirated, with the results shown below.
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Results
Joint
Colour\: yellow
Clarity\: opaque
Viscosity\: decreased
WBC\: 60,000 mm³
Neutrophils\: 90 %
Gram stain\: negative
Answer
Septic arthritis (the most likely causative organism is Neisseria gonorrhoeae)

Case 2

A 25-year-old male presents with pain in the metacarpophalangeal (MCP) joints of both hands. He has morning joint sti
that lasts for more than an hour. On examination, you note multiple warm, swollen MTP joints, with associated erythema. The
largest joint e
Results
Joint
Colour\: yellow
Clarity\: cloudy
Viscosity\: decreased
WBC\: 40,000 mm³
Neutrophils\: 60 %
Gram stain\: negative
Answer
In

Case 3

A 67-year-old female presents with left knee sti
worsened over the last 8 years and she is now struggling to mobilise outside. On examination, there is left knee swelling, with
signi
sweep test on assessment and the e
Results
Joint
Colour\: colourless
Clarity\: translucent
Viscosity\: increased
WBC\: 1500 mm³
Neutrophils\: 15 %
Gram stain\: negative
Answer
Non-in

References

1. Abdullah S, Young‐Min SA, Hudson SJ, Kelly CA, Heycock CR, Hamilton JD. Gross synovial
diagnosis of joint e
2. Goldenberg DL. Bacterial arthritis. In\: Ruddy S, Harris ED, Sledge CB, Kelley WN, eds. Kelley's Textbook of Rheumatology. 6th
ed. Philadelphia, Pa.\: Saunders; 2001\:1469–1483.
3. Schumacher HR Jr. Synovial
Textbook of Rheumatology. 6th ed. Philadelphia, Pa.\: Saunders; 2001\:605–619.
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