Notes on Body Fluids, CSF, Serous/Synovial Fluids, and BAL

: Specimen Collection and Processing

• MUST be tested within 1 hour of collection to avoid cellular degradation and lysis, which yields falsely low WBC/RBC counts. Do not discard sample until testing is completed.

• Collected in sterile non-anti-coagulated tubes; typical procedure uses 3 or 4 tubes, each containing about 2–4 mL of CSF, collected in a specific order.

• Tube allocation:

  • Tube #1: Chemistry (protein, glucose, lactate).

  • Tube #2: Microbiology (Gram stain, cultures, other tests).

  • Tube #3: Hematology (cell counts, differential, colour/appearance).

  • Tube #4: Reserved for additional chemistry, hematology, cytology, serology, flow cytometry, molecular tests, etc.

• After analysis, refrigerate samples if additional tests may be required; do not refrigerate samples destined for microbiology, as some organisms (e.g., Neisseria meningitidis) can be destroyed by refrigeration. Prefer incubation at ~37°C when testing.

• CBC and chemistry testing should be performed with CSF blood draw to obtain a complete picture.

• Indications for CSF collection include suspicion of meningitis, subarachnoid hemorrhage, CNS malignancy, and demyelinating diseases.

• CSF collected between L3 and L4 using sterile technique.

• CSF production and total volume:

  • CSF production rate: $\dot{V}_{CSF} \approx 20\ \frac{\text{mL}}{\text{hr}}$

  • Adults total CSF volume: $V_{CSF,\text{adult}} \approx 90\text{ mL to }150\text{ mL}$

  • Children: $V_{CSF,\text{child}} \approx 60\text{ mL to }100\text{ mL}$

  • Neonates: $V_{CSF,\text{neonate}} \approx 10\text{ mL to }60\text{ mL}$

CSF: Macroscopic examination

• Normal CSF: non-viscous (watery), clear and colorless.

• Cloudy CSF indicates possible infection with increased WBC/RBC and protein elevation.

• Blood in CSF can indicate: traumatic tap vs pathology (subarachnoid hemorrhage).

  • Traumatic tap: blood present in first tube, clearing in subsequent tubes.

  • Pathologic hemorrhage: blood present in all tubes.

• Color assessment:

  • Yellow/pinkish yellow may indicate subarachnoid hemorrhage; yellow (xanthochromia) may be pathologic but not always.

  • CLSI guidance: report color as observed; color alone is not definitive for diagnosis.

• Procedure for bloody samples: centrifuge an aliquot to examine supernatant for color change; clear supernatant supports traumatic tap; yellow supernatant supports possible subarachnoid hemorrhage.

CSF: Cell counts and differential

• Normal reference ranges (CSF cells per microliter):

  • Adults: $0 \le \text{WBC} \le 5\;\frac{\text{cells}}{\mu L},\quad \text{RBC} \approx 0\;\frac{\text{cells}}{\mu L}$

  • Neonates: $0 \le \text{WBC} \le 30\;\frac{\text{cells}}{\mu L},\quad \text{RBC} \approx 0\;\frac{\text{cells}}{\mu L}$

  • WBC/RBC counts are reported in units of $\frac{\text{cells}}{\mu L}$ or $\times 10^6/\text{L}$ as per the lab SOP.

• When counts are high or sample turbid, dilutions may be required to obtain accurate WBC/RBC counts. Typical diluent for RBCs is isotonic saline; for WBCs, glacial acetic acid (Türk solution) or a prepared Türk solution (glacial acetic acid with methylene blue).

• Dilution guidance:

  • If sample slightly bloody: undiluted RBCs may be counted, but WBCs may require a dilution (e.g., 1:2 or 1:10 with Türk solution).

  • If heavily bloody: use dilutions such as 1:200 for RBCs and 1:2 or 1:10 for WBCs.

• Hemocytometer usage:

  • Typically count all nine squares on both sides of the hemocytometer for fluids; adjust the calculation if fewer squares are counted due to high counts.

• Important considerations:

  • Make sure pipets are calibrated properly before use.

  • Synovial fluids require special handling (see Synovial Fluid section) and acetic acid cannot be used due to hyaluronic acid coagulation.

CSF: Differential cell types and abnormal findings

• Common qualitative findings:

  • Normally, CSF contains lymphocytes and monocytes in small numbers; neutrophils are not typical.

  • Neutrophils may appear early in bacterial meningitis; elevated WBC with neutrophils prompts bacterial workup.

  • Viral meningitis: predominantly lymphocytes; reactive/viral lymphocytes may appear.

  • Nucleated RBCs indicate bone marrow contamination (puncture involving vertebral body).

• Less common cellular findings:

  • Ependymal cells and choroid plexus cells (large with abundant cytoplasm; lavender-staining; appear in clumps; not diagnostic; can mimic malignant cells).

  • Cartilage cells (from vertebral body contamination).

  • Siderophages (macrophages containing hemosiderin) appear ~48 h after hemorrhage and persist up to 2–8 weeks; may contain bilirubin (hematoidin crystals).

  • Erythrophages (monocyte ingest RBCs).

  • Signet ring cells (lipid-laden cells with large vacuole displacing nucleus).

  • Lupus erythematosus cells may be seen in certain patients; report when identified.

  • Neoplastic cells may be present in tumor/meningeal metastasis; cytology is required for confirmation.

CSF: Cytospin preparation and cytology

• Once CSF WBC/RBC counts are established, prepare cytocentrifuge (cytospin) slides for differential and cytology.

• Cytospin slides enable identification of rare or abnormal cells (e.g., ependymal/choroid cells, tumor cells, erythrophages, siderophages).

• Instrument and slide quality, and cytology interpretation are typically covered in the SOP and lab protocol.

Serous body fluids: overview and classification

• Serous effusions are accumulations of fluid in serous cavities and are subdivided into transudates and exudates.

• Pathophysiology:

  • Transudates: result from increased hydrostatic pressure or decreased oncotic pressure; generally less protein and fewer inflammatory cells; associated with conditions such as congestive heart failure, kidney failure, liver failure.

  • Exudates: result from inflammation or infection causing increased vascular permeability; higher protein and LDH; associated with infections, inflammatory diseases, malignancies, and others.

• Appearance varies by type and etiology: straw-colored/translucent (transudates); cloudy/yellow (exudates); bloody (trauma or malignancy); milky (chyle).

Serous fluids: transudates vs exudates – key criteria (Table 15.4 concepts)

• Specific gravity (SG):

  • Transudates: SG < 1.016

  • Exudates: SG > 1.016

• Protein concentration (in g/dL):

  • Transudates: Protein < 3 g/dL

  • Exudates: Protein > 3 g/dL

• Lactate dehydrogenase (LDH):

  • Transudates: LDH < 200 IU

  • Exudates: LDH > 200 IU

• White blood cell count (per microliter):

  • Transudates: < 1000/µL (predominant mononuclear cells)

  • Exudates: > 1000/µL

• Protein:fluid-to-serum ratio and LDH:fluid-to-serum ratio thresholds

  • Transudates: Protein:fluid-to-serum ratio < 0.5; LDH:fluid-to-serum ratio < 0.6

  • Exudates: Protein:fluid-to-serum ratio > 0.5; LDH:fluid-to-serum ratio > 0.6

• Color and appearance: Transudates typically clear; Exudates may be cloudy or yellow.

• Volume: Transudates generally involve smaller volumes; Exudates may be extremely large depending on the pathology.

Serous fluids: appearance and differential cellular content

• Normal cellular constituents include:

  • Lymphocytes, histiocytes (macrophages), and mesothelial cells.

• Neutrophils: presence indicates an abnormal/infectious process; high numbers may accompany acute inflammation.

• Mesothelial cells: lining cells with a characteristic “fried egg” appearance; basophilic cytoplasm, oval nucleus; can be multinucleated; cell borders smooth; seen in many effusions; elevated in sterile inflammation and decreased in infections.

• Macrophages/histiocytes: monocytes/macrophages; may contain erythrophages or siderophages.

• Erythrophages and siderophages: indicators of bleeding within the cavity; siderophages contain hemosiderin; bilirubin crystals (hematoidin) may be seen.

• Signet ring cells: lipid uptake producing large vacuole; not diagnostic for a specific disease.

• Neutrophils: not normally abundant; elevated numbers prompt bacterial consideration.

• Lupus erythematosus (LE) cells: may be seen in patients with lupus; should be reported when identified.

• Tumor cells: may be present in primary or metastatic malignancies; cytology required for confirmation.

Serous fluids: flow and processing (cytology workflow)

• Cytocentrifuge slide preparation (cytospin) used to concentrate cells for differential and cytology.

• If infection suspected: perform Gram stain on cytocentrifuge slide and corroborate with culture results.

• When cytology detects tumor cells or unusual cells, escalate to cytology laboratory for definitive diagnosis.

Synovial fluid: overview and handling

• Baseline appearance: normally straw-colored, clear, viscous fluid.

• Cellular constituents: normally include lymphocytes, monocytes, histiocytes, and synovial lining cells; LE cells may be present in disease.

• Neutrophils: present in higher numbers with inflammatory processes; search for bacteria.

• Crystals can be detected in synovial fluid and are critical for diagnosis of crystal arthropathies.

Synovial fluid: crystals and polarized light interpretation

• Monosodium urate (MSU) crystals: needle-like crystals; intercellular and extracellular in appearance; strongly birefringent; appear yellow when crystal axis is parallel to the polarized light axis; seen in gout.

• Calcium pyrophosphate dihydrate (CPPD) crystals: rhomboid-shaped crystals; intracellular (often) or extracellular; weakly birefringent; appear blue when oriented in a certain way (or yellow, depending on orientation) under polarized light; associated with pseudo-gout.

• Cholesterol crystals: large, flat, extracellular crystals with notched corners; seen in chronic effusions (e.g., rheumatoid arthritis).

Synovial fluid: processing and counts

• WBC staining and dilutions: Türk solution (1:2 or 1:20) or other dilutions may be used; RBC dilutions commonly 1:200.

• Hyaluronidase: added to synovial fluid to liquefy viscous samples before cell counting.

• Cytospin slides: prepared for differential and micro analysis; look for bacteria on Gram stain.

• Cytology reports should include presence of LE cells if identified; report crystal polarizations to confirm crystal type.

• Reported elements:

  • Crystals: MSU, CPPD, and cholesterol crystals (polarize to confirm).

  • Cells: segmented neutrophils, lymphocytes, histiocytes/monocytes; synovial lining cells; synovial cells; bacteria; LE cells.

Bronchoalveolar lavage (BAL) specimen

• BAL procedure entails washing the lungs with warm saline and then retrieving the lavage fluid to sample areas not easily accessible.

• Indications: performed in patients with severe lung dysfunction; requires extensive microbiologic work-up.

• Handling and safety: samples should be mixed and opened in a biosafety cabinet to avoid aerosol release; high risk for cell counts and cytospin preparations.

• Common cell findings:

  • Neutrophils, macrophages, and lymphocytes are the most common cell types.

  • Ciliated epithelial cells: presence indicates sampling from the upper respiratory tract, not deep lung; should be reported.

  • Histocytes laden with carbonaceous material (e.g., tobacco exposure).

  • Pneumocystis jirovecii (carinii) infection can be detected in BAL samples, particularly in HIV-infected patients.

• Polarization and cytospin evaluation may assist in identifying specific organisms and cell types.

Cytocentrifuge: slide preparation for cellular evaluation

• Cytospin slides are prepared after counts are obtained to enable cellular differential and cytology assessment.

• Review and SOPs generally reference cytospin preparation steps and relevant educational videos.

Practical references and context

• Core reference for these notes: Rodak’s Hematology: Clinical Principles and Applications, 6th edition (Chapter 15) and related Essentials of Human Anatomy and Physiology resources.

• Important considerations:

  • Always follow lab SOPs for dilution, counting, and reporting units.

  • Ensure proper sample handling to avoid degradation and contamination (e.g., upper airway contamination in BAL).

  • Distinguish transudates from exudates using SG, protein, LDH, WBC, and fluid-to-serum ratios, along with clinical context.

Quick example question (illustrative) from serous fluid interpretation

• Pericardial fluid with results: SG = 1.010, WBC = 850/µL with 85% lymphocytes, color clear and straw-yellow.

  • Classification: Transudate (SG < 1.016; WBC < 1000/µL; predominant lymphocytes) rather than exudate; however, clinical correlation is required as exudates can occasionally present with similar values.

Summary of key numeric thresholds for quick review

• CSF normal (adult): WBC ∈ [0, 5] /µL; RBC ≈ 0 /µL

• CSF normal (neonate): WBC ∈ [0, 30] /µL; RBC ≈ 0 /µL

• CSF production: $\dot{V}_{CSF} \approx 20\ \frac{\text{mL}}{\text{hr}}$

• Total CSF volumes: adults 90–150 mL; children 60–100 mL; neonates 10–60 mL

• Transudates vs Exudates (key criteria):

  • SG: < 1.016 vs > 1.016

  • Protein: < 3 g/dL vs > 3 g/dL

  • LDH: < 200 IU vs > 200 IU

  • WBC: < 1000/µL vs > 1000/µL

  • Protein:fluid-to-serum ratio: < 0.5 vs > 0.5

  • LDH:fluid-to-serum ratio: < 0.6 vs > 0.6

• Common BAL cell types: neutrophils, macrophages, lymphocytes; ciliated epithelial cells indicate upper airway contamination

• Typical synovial crystal findings: MSU (needle-like, strongly birefringent), CPPD (rhomboid, weakly birefringent), cholesterol crystals (extracellular, notched).

CSF

References

• Rodak’s Hematology: Clinical Principles and Application; Chapter 15, Sixth Edition (and related pages 237–244, 248).

• Essentials of Human Anatomy and Physiology, 13th edition (meninges, CSF production, Blood–brain barrier context).