What if no synovial fluid is obtained

What if no synovial fluid is obtained (a “dry tap”)?

Even if no fluid is aspirated into the syringe, frequently one or two drops of fluid and/or blood can be found within the needle and its hub. This amount is sufficient for culture, in which case the syringe with a capped needle should be submitted to the microbiology laboratory. If one extra drop can be spared, it can be placed on a microscope slide with a coverslip for estimated cell count (1 white blood cell [WBC]/40 × objective = 500 WBCs) and polarized microscopy. When microscopy is completed, the coverslip can be removed and the specimen may then serve as a smear for Gram stain. The specimen remaining on the coverslip may be an adequate smear on which to perform a Wright stain, allowing determination of leukocyte differential. Thus, two drops of fluid can yield the same important diagnostic information as that obtained from a larger specimen, with the exception of a leukocyte count. The lesson to be learned from this is that when a “dry tap” is encountered, the needle and syringe should not be reflexively discarded.

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