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Body fluid counts and CSF appearance

15 min

Skills you'll build3 skills
  • Choose manual confirmation when a body-fluid count falls outside the verified range
  • Recognize cytocentrifuge distortion that mimics abnormal cells on a body-fluid slide
  • Name the abnormal findings that a clear, colorless CSF can still contain

At the bench: Coordinate cell examination and chemistry for a body fluid specimen

Try first

Try first

An adult's clear CSF runs in the analyzer's body-fluid mode and gives a nucleated cell count of 3/µL. The laboratory verified this mode from 10/µL upward. What do you report?

Keep going to see the reasoning.

Keep going to see the reasoning.

Right. Keep going to follow the reasoning.

Keep going to see the reasoning.

Keep going to see the reasoning.

Get the idea

Use the explanation to check your first decision.

Count in the verified range

An automated body-fluid mode is fast and precise inside the range the laboratory verified for that fluid. Near its lower limit it loses accuracy. Debris, crystals, microorganisms and atypical cells can also be counted as the wrong kind of cell.1,2 The laboratory documents which fluids each mode may count, its reportable range, and the flags that send a specimen to a manual count or a morphology review.1,3

Normal adult lumbar CSF contains no more than a few nucleated cells per microliter.1 A normal CSF therefore falls at the bottom of the analyzer's range, where the method is least accurate. A count below the verified range, a flag, or a fluid the mode was never verified for goes to a hemacytometer. A Fuchs-Rosenthal chamber is 0.2 mm deep with a 16 mm² ruled area, so it counts a larger volume and is used for CSF with few cells.1

Cytocentrifuge preparations

A cytocentrifuge spins a low-cell fluid onto one small area of a slide. The spin can tear cytoplasm, distort nuclei and push cells into clusters. These changes can look like malignant or reactive cells.1,2

  1. Scan the whole deposit at low power for clumps, organisms and abnormal cells.
  2. Classify cells at high power, usually 100 of them.
  3. When fewer cells are present, report how many cells were classified.
  4. Send unexpected atypical cells for review by qualified staff.

A negative preparation from a low-cell specimen cannot exclude malignancy.1

A clear CSF can still be abnormal

Normal CSF is clear and colorless. A clear specimen can still have an abnormal cell count, organisms, malignant cells or abnormal chemistry. Appearance is an early finding, and the counts and ordered tests are still performed.1

Xanthochromia is color in the cell-free supernatant. Bilirubin and oxyhemoglobin form over hours after bleeding, so a very recent hemorrhage can leave the supernatant clear. The time from symptom onset to collection is reported with every xanthochromia result.1,4 Fewer red cells in each later tube supports a traumatic collection, and it cannot rule out a hemorrhage.1

Follow the bench demonstration

Sources for this step
References
  1. Keohane EM, Preston MM, Mirza KM, Walenga JM, eds. Rodak's Hematology: Clinical Principles and Applications. 7th ed. Elsevier; 2025. Accessed September 27, 2026. https://www.us.elsevierhealth.com/rodaks-hematology-9780323936507.html
  2. Alcaide Martín MJ, Altimira Queral L, Sahuquillo Frías L, et al. Automated cell count in body fluids: a review. Adv Lab Med. 2021;2(2):149-177. doi:10.1515/almed-2021-0011
  3. Bourner G, De la Salle B, George T, et al. ICSH guidelines for the verification and performance of automated cell counters for body fluids. Int J Lab Hematol. 2014;36(6):598-612. doi:10.1111/ijlh.12196
  4. National Institute for Health and Care Excellence. Subarachnoid haemorrhage caused by a ruptured aneurysm: diagnosis and management. NICE guideline NG228. Published November 23, 2022. Updated December 4, 2025. Accessed September 27, 2026. https://www.nice.org.uk/guidance/ng228/chapter/Recommendations

Watch one

Read each decision and its explanation.

Tube 3 of an adult's lumbar CSF reaches the laboratory 20 minutes after collection. It contains 1.5 mL.

The laboratory verified the body-fluid mode for CSF from 10/µL upward. What nucleated cell count is reported?

TestResultReference intervalFlag
Nucleated cells, analyzer body-fluid mode4 /µL0–5 /µL0–5
Analyzer messageDebris flag

Specimen: Not measured on body fluids. CSF, tube 3, lumbar; clear and colorless, no clot

  1. Inspect the specimen: clear, colorless and free of clots.

    A clot or visible particles would change every count, so the tube is inspected before it is mixed.

  2. Compare the count with the verified range: 4/µL is below 10/µL, so it is not reportable.

    A number below the verified range has no demonstrated accuracy.

  3. Read the flag: debris is a second reason for a manual count.

    The debris flag indicates the analyzer may have counted particles as cells.

  4. Load a 1:2 dilution in a lysing diluent into both sides of a Fuchs-Rosenthal chamber and count all 16 mm² on each side: 12 and 14 cells.

    A low-cell fluid needs a large counted volume to give a stable count.

  5. Check agreement: 12 and 14 meet the laboratory's limit for sides this low.

    The two sides are independent measurements, so their agreement is checked before they are pooled.

  6. Calculate: 26 cells × 2 ÷ 6.4 µL = 8.1 cells/µL.

    Each side counts 16 mm² × 0.2 mm = 3.2 µL, so both sides together count 6.4 µL.

The reported count is 8 nucleated cells/µL from the manual chamber count, above the 0 to 5/µL interval. The analyzer's 4/µL is not reported.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

A cytocentrifuge slide from a CSF with 6 nucleated cells/µL shows mostly lymphocytes and monocytes. Near the edge of the deposit sit two clusters of large cells with folded nuclei and frayed cytoplasm. What do you do with the clusters?

Spinning can distort nuclei, tear cytoplasm and clump cells, and the result can look malignant. Reporting them as malignant would report a preparation artifact as disease.

Treated cytocentrifuge distortion as disease

Cytocentrifugation can disrupt cytoplasm, distort nuclei, and clump cells, and these changes can resemble malignant or reactive cells. Reporting them as disease mislabels a preparation artifact. Refer unexpected atypical cells for qualified review.

The clusters could be true atypical cells. Omitting them leaves out a finding that qualified staff need to see.

Distortion from the spin can mimic abnormal cells, and real abnormal cells also occur in CSF. Review by qualified staff determines which these are.

A cytocentrifuge slide from a low-cell specimen cannot exclude malignancy, and these clusters have not been identified.

Hint
  1. Consider what the spin does to cells.
  2. Consider who is qualified to identify an unexpected cell population.

Review Preparing a stained differential

Problem 2 of 3 · Hints available

CSF is collected 3 hours after the sudden onset of a severe headache. Tube 4 is clear, and after centrifugation the supernatant is colorless. How is the colorless supernatant interpreted?

The pigments that color the supernatant form over hours. At 3 hours a real hemorrhage can still leave it colorless.

Used a clear appearance to exclude infection or hemorrhage

Clear CSF can still contain an abnormal cell count, organisms, malignant cells, or a very recent hemorrhage without xanthochromia. Reporting a clear specimen as normal on appearance skips the counts and tests that detect them.

A colorless supernatant fits a traumatic collection, and it also fits a very recent hemorrhage. It cannot tell the two apart this early.

Pigments form over hours after bleeding. A result from 3 hours after onset is interpreted with that timing, and the counts on each tube are still performed.

Hint
  1. Bilirubin and oxyhemoglobin come from red cells that have been in the CSF for some hours.
  2. Compare 3 hours with the time these pigments need to form.

Review Appearance and blood contamination

Problem 3 of 3 · On your own

The laboratory verified its analyzer's body-fluid mode for pleural and peritoneal fluids. It has not verified the mode for CSF, although the analyzer offers a CSF setting. A CSF arrives for a cell count. How is it counted?

The laboratory's own verification for CSF determines which methods may be used to count it. Low CSF counts from an unverified mode could report a normal count a chamber would not confirm.

Released a low automated count outside its verified range

Automated body-fluid modes lose accuracy near their lower limit and can misclassify debris, crystals, or atypical cells. Releasing a low CSF count from the analyzer outside its verified range can report a normal count that a manual chamber count would not confirm.

A comment leaves an unverified number in the chart. The count needs a method the laboratory has shown to work for CSF.

The CSF mode is outside what the laboratory verified, so a hemacytometer count gives the reportable result.

Review Selecting and controlling a cell-count method

Use it

Read the case evidence, then make each decision. The step is complete without it.

  • Ruth Boyle, 58, MRN 4407123, has four CSF tubes collected at 10:40.
  • Her headache began suddenly at 08:00.
  • Tube 1 is pink. Tube 4 is clear, and its supernatant is colorless.
  • Tube 4's nucleated count by analyzer is 2/µL. The mode is verified for CSF from 10/µL upward.
  • The cytocentrifuge slide holds 38 cells, with one tight cluster of cells with smudged cytoplasm.
Decision 1 of 3

What does tube 4's appearance allow you to report?

A clear specimen can still contain abnormal cells, organisms or blood from a recent hemorrhage. The ordered tests detect those findings.

Used a clear appearance to exclude infection or hemorrhage

Clear CSF can still contain an abnormal cell count, organisms, malignant cells, or a very recent hemorrhage without xanthochromia. Reporting a clear specimen as normal on appearance skips the counts and tests that detect them.

The appearance is reported as seen. At 2 hours 40 minutes after onset, a colorless supernatant cannot exclude a hemorrhage, and the pink tube 1 still needs an explanation.

Clearing across the tubes supports a traumatic collection. It cannot rule out a hemorrhage, and both can occur together.

Review Appearance and blood contamination

Decision 2 of 3

What do you do with the analyzer's 2/µL?

The count is below the verified range, so its accuracy is unknown.

Released a low automated count outside its verified range

Automated body-fluid modes lose accuracy near their lower limit and can misclassify debris, crystals, or atypical cells. Releasing a low CSF count from the analyzer outside its verified range can report a normal count that a manual chamber count would not confirm.

A chamber count gives an accurate result below the analyzer's verified range. The chamber count is the one released.

The comment states that the number is unverified and still puts it in the chart. A chamber count gives a reportable result within minutes.

Review Selecting and controlling a cell-count method

Decision 3 of 3

How is the differential reported?

Only 38 cells were classified, and smudged clustered cells can be a spin effect. Neither the denominator nor the identification would be correct.

Treated cytocentrifuge distortion as disease

Cytocentrifugation can disrupt cytoplasm, distort nuclei, and clump cells, and these changes can resemble malignant or reactive cells. Reporting them as disease mislabels a preparation artifact. Refer unexpected atypical cells for qualified review.

The report states how many cells were classified. The cluster goes to qualified staff, who identify it.

The count of 38 is correct. Omitting the cluster leaves out a finding that needs review.

Review Preparing a stained differential

The interpretation depends on the time from onset to collection. At 2 hours 40 minutes the pigments may not have formed, so the clear, colorless tube 4 excludes nothing. Every count and test is performed, the low count comes from a chamber, and the unidentified cluster goes for review.

For reference

Sources checked