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Finding the right tests…
Haematology
DLC (Fluid) applies the same idea as a blood differential count to a body fluid instead - most often cerebrospinal fluid from a lumbar puncture, or fluid drawn from the chest or abdomen. Normal cerebrospinal fluid holds barely any white cells, so even a small number showing up, and which type they are, carries more weight here than the same finding would in blood. A neutrophil-heavy fluid sample points toward a bacterial cause; a lymphocyte-heavy one points more toward a viral or tuberculous cause. Because normal fluid starts with so few cells, this count is read alongside the fluid's protein, glucose and appearance, not as a number on its own.
The result reports what percentage of the white cells present in the fluid are neutrophils versus lymphocytes, plus any other cell types seen, alongside the total cell count. In cerebrospinal fluid, a normal result is close to zero to five cells per cubic millimetre, essentially all lymphocytes or monocytes. A count running into the hundreds with mostly neutrophils looks very different clinically from a similar total made up mostly of lymphocytes, even though both are abnormal totals.
In blood, a shift toward more neutrophils or more lymphocytes is one clue among many. In a fluid that is normally almost cell-free, like cerebrospinal fluid, any clear shift is a much stronger signal, because there is so little background noise to begin with.
Research on meningitis has shown bacterial cases typically produce cell counts in the high hundreds to low thousands, overwhelmingly neutrophils, while viral meningitis produces lower counts, usually under a thousand, dominated by lymphocytes. Tuberculous meningitis tends to sit in between, also lymphocyte-heavy. None of these patterns is exclusive on its own - a doctor weighs it with protein, glucose and culture results together.
- Working out whether suspected meningitis looks bacterial, viral or tuberculous - Checking fluid drawn from the chest or abdomen when infection or cancer is suspected - Following how an infection is responding to treatment over repeat fluid samples
This test almost always needs the fluid to be collected by a doctor first, through a procedure like a lumbar puncture. Ask your doctor how the fluid in your case will be collected and what to expect afterward.
A regular DLC is run on blood. DLC (Fluid) is run on a body fluid such as cerebrospinal fluid, chest fluid or abdominal fluid, which normally contains far fewer cells than blood, so even small changes matter more.
It leans toward a viral or tuberculous cause rather than a typical bacterial one, though it does not rule bacterial infection out completely. Your doctor reads it alongside other fluid findings and your symptoms.
It leans toward a bacterial cause, especially when the total cell count is also high. This pattern often prompts urgent treatment while further test results, like culture, are awaited.
This page is general information about the test, not medical advice. Your own report's reference ranges apply — please discuss your results with your doctor.
Cerebrospinal fluid is collected by a doctor through a lumbar puncture, or spinal tap. Chest or abdominal fluid is collected through a needle drainage procedure. Both are done by a trained clinician, not at a routine blood draw.
No. Normal cerebrospinal fluid has close to zero to five white cells per cubic millimetre, which is dramatically lower than the normal range in blood. Ranges vary by lab and by which fluid is tested.
No. It is one part of a fluid analysis that also includes protein, glucose and often culture testing. Your doctor combines all of these with your symptoms before reaching a diagnosis.