Required section · Section 2 of 6
How one collection becomes four results
A serous-fluid collection is not one specimen for one test. It is split into aliquots that each protect a different downstream result. An EDTA aliquot, well mixed and free of clot, goes to the cell count and differential. A sterile container with no anticoagulant goes to microbiology and, when ordered, cytology. A plain aliquot goes to chemistry for protein, LDH, glucose, triglyceride, or amylase. A heparinized blood-gas syringe, filled anaerobically with no air bubble, goes to pH.
Gross appearance is recorded before aliquoting, not inferred afterward. Opaque, bloody, turbid, or milky appearance is an observation, not a diagnosis; it gets correlated with the cell count, the differential, and the collection circumstances rather than reported on its own as a conclusion. A clotted cellular-analysis specimen is a problem for the cell count and differential specifically, and the laboratory's rejection or qualification policy decides whether that aliquot can still be counted.
The process map below lays out that routing decision the way it happens at the bench: confirm the site, inspect the specimen, then send each aliquot to the container and test it was drawn for. Skipping a step, for example running chemistry on a clotted aliquot without checking the policy, can invalidate the result before any calculation happens.
Decide the aliquot destinations and inspect the specimen before anything is centrifuged, diluted, or plated, because that order protects every result that follows.
Routing one serous-fluid collection from receipt to four test destinations.
Confirm collection site
Match the tube label to the order: pleural or peritoneal. This determines which classification framework will apply later, so it is checked before any aliquot is made.
Inspect gross appearance and clot
Record color and clarity, and check for clot before mixing or splitting the specimen. A clotted cellular aliquot is handled under the rejection or qualification policy.
Aliquot by destination
Send a well-mixed EDTA aliquot to cell count and differential, a sterile aliquot to microbiology and cytology, a plain aliquot to chemistry, and an anaerobic heparinized syringe to pH.
Pair with serum
For chemistry ratios such as Light's criteria, confirm a same-encounter serum sample is drawn or already available so the paired calculation reflects the same clinical interval.
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