Synovial Fluid Analysis – Made Easy

What investigations to order for synovial fluid sample?

Mnemonic: 5 Cs

  1. Chemistry (pH, LDH, glucose, protein)
  2. Cell counts
  3. Cytology
  4. Culture
  5. Crystals
polarized microscopy
Cholesterol crystals in polarized microscopy
Ed Uthman, MD, pathologist, Houston, Texas, USA / CC BY

Interpretation of synovial fluid analysis

GrossNormalNon-inflammatoryInflammatorySepticCrystalHemorrhagic
Volume (ml)<3.5>3.5>3.5>3.5>3.5>3.5
ViscosityHighHighLowVariableVariableVariable
ColorColorless to strawStraw to yellowYellow
Cloudy
Yellow-white
Cloudy
Yellow
Cloudy
Red
Xanthochromic
Routine lab
WBC<200200-20002000-75000Often >1000002000-7500050-10000
PMN (%)<25<25>50>75>50<50
CrystalsNegativeNegativeNegativeNegativePositiveNegative
Mucin clotFirmFirmFriableFriableFriable
Glucose (AM fasting)Nearly equal to bloodNearly equal to blood<50 mg% lower than blood>50 mg% lower than blood>50 mg% lower than bloodNearly equal to blood
ExamplesOA, Trauma, AVN, SLERA, Reiter’s, SLE, Viral, Fungal, TBBacterialGout, PseudogoutTrauma, fracture, ligament tear, hemophilia, charcot arthritis, PVN
OA – Osteoarthritis; AVN – Avascular necrosis; SLE – Systemic Lupus Erythematosus; RA – Rheumatoid Arthritis; TB – Tuberculosis; PVNS – Pigmented Villonodular Synovitis

Crystals in Gout and Pseudogout

Mnemonic: “P” for Pseudogout

Pseudogout:

  • Polarized microscopy
  • Positive birefrengence
  • Pyrophosphate crystals
  • Polygon (Rhomboid) shaped
  • Purple (blue) color

Gout:

  • Negative birefrengence
  • Needle shaped
  • Urate crystals
  • Yellow color

Mnemonic: Look for ABC (Alignment, Blue, Calcium) in crystal analysis. If the crystal aligned with the red-plate compensator is blue, it is calcium pyrophosphate dihydrate. Urate crystals are the opposite, being yellow when parallel to the compensator.

References:

1. Clinical Laboratory Medicine edited by Kenneth D. McClatchey

2. Rheumatology Secrets By Sterling G. West


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