Required section · Section 2 of 6
How the aliquots move through the lab
Synovial fluid normally contains little or no fibrinogen, but an inflammatory effusion can contain enough fibrinogen to clot even when collection is handled correctly, so a clot in a non-anticoagulated tube is a specimen finding to document rather than a sign that collection was done wrong. A clot can trap cells and make the total nucleated cell count unreliable. The laboratory's own rejection or conditional-release policy decides whether a clotted tube still supports a differential or a crystal search.
Liquid ethylenediaminetetraacetic acid (EDTA) is a published option for count, differential, viscosity, and crystal work, but that acceptance is not automatic. Anticoagulant choice is a local validation decision: oxalate, lithium heparin, and powdered EDTA can each generate crystal-like material under the microscope, so an unvalidated tube cannot be used to support a crystal identification even if it looks acceptable for a cell count.
Synovial fluid in an additive-free container can also be examined directly for crystals. Anticoagulants do not preserve monosodium urate (MSU) or calcium pyrophosphate (CPP) crystals any better than an additive-free specimen does, so choose the crystal container for a clean preparation, not because an additive protects the crystal.
Time is part of the specimen, not an afterthought. Published guidance calls for room-temperature transport promptly after collection, commonly within about one hour, because delay can reduce leukocyte counts and shift optical characteristics before the fluid is ever examined. A crystal search is best done on fresh aspirate within 24 hours to preserve the intracellular-crystal context, though MSU and CPP crystals may still be found after a short delay.
Record collection time and examination time on every synovial fluid report, because a delayed or mishandled specimen can look inflammatory or crystal-negative for reasons that have nothing to do with the joint.
Aliquot triage for a synovial fluid aspirate arriving with count, differential, and crystal orders
Inspect on arrival
Check each tube for a clot, note fill volume, record collection and receipt times, and confirm which aliquot is sterile and additive-free.
Protect the sterile aliquot
Reserve the native, additive-free tube for microbiology first when volume is limited, and notify the collector if that aliquot is missing or compromised.
Prepare the count and differential aliquot
Use the liquid-EDTA fluid, or another locally validated anticoagulant, for the manual or automated cell count and for a stained cytocentrifuge differential.
Prepare the crystal aliquot
Use native, additive-free fluid for the wet preparation crystal search, since anticoagulant does not improve crystal preservation and some additives generate look-alike material.
Document specimen limitations
Carry any short fill, clot, or delay forward onto the report with the affected result, rather than silently dropping the limitation.
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