Which knee arthrocentesis results are characteristic of septic joint effusion?

Updated: Nov 03, 2020
  • Author: Gil Z Shlamovitz, MD, FACEP; Chief Editor: Erik D Schraga, MD  more...
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Answer

Synovial fluid characteristics associated with septic joint effusion are as follows:

  • Total white blood cell (WBC) count higher than 25,000/µL (sensitivity, 77%; specificity, 73%; positive likelihood ratio [LR +], 29; negative likelihood ratio [LR ], 0.71)
  • Total WBC count higher than 50,000/µL (sensitivity, 62%; specificity, 92%; LR +, 7.7; LR , 0.42) [9]
  • Total WBC count higher than 100,000/µL (sensitivity, 22%; specificity, 99%; LR +, 2.9; LR , 0.32)
  • PMN cell proportion 0.9 or higher (sensitivity, 73%; specificity, 79%; LR +, 3.4; LR , 0.34)
  • Synovial glucose or serum glucose concentration lower than 0.5 (sensitivity, 51%; specificity, 85%; LR +, 3.4; LR , 0.58)
  • Protein concentration higher than 3 g/dL (sensitivity, 48%; specificity, 46%; LR +, 0.9; LR -, 1.1)
  • Lactic dehydrogenase (LDH) concentration higher than 250 U/L (sensitivity, 100%; specificity, 51%; LR +, 1.9; LR , 0.1)

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