AK

unit 6 Body Fluids – Quick Reference Notes (Last-Minute)

Cerebrospinal Fluid (CSF)

  • Definition and role: clear, colorless, sterile fluid circulating in brain ventricles, subarachnoid spaces, and central canal; cushions CNS and provides nutrient medium; not an ultrafiltrate of plasma due to blood–brain barrier
  • Volume and composition: adults have 90\text{--}150\,\text{mL}; contains ~99% water; no RBCs; low protein and lipids compared with serum; CSF protein ~35\,\text{mg/dL}; glucose ~60\,\text{mg/dL}; pH ~7.33; osmolarity ~295\,\text{mOsm/L}
  • Four main functions: mechanical buffering, intracranial volume regulation, CNS nutrition, excretion of CNS metabolites
  • Indications for collection: meningitis diagnosis, cerebral hemorrhage, neurological disease, suspected malignancy, administration of drugs/contrast
  • Sample handling (CSF):
    • Collect via lumbar puncture under sterile conditions; deliver STAT to lab immediately
    • Typical collection: 3–4 sterile tubes (~1 mL each), labeled 1–4
    • Tube roles:
    • Tube 1: chemistry (e.g., glucose, protein, xanthochromia)
    • Tube 2: microbiology (Gram stain, culture)
    • Tube 3: hematology (total cell counts, differential)
    • Tube 4: cytology
  • Storage and retention:
    • Some tests refrigerated or frozen; microbiology tubes at room temp
    • Follow SOPs for CSF storage; retention varies by department
  • Analysis goals:
    • Diagnose CNS disorders: meningitis, encephalitis, hemorrhage, tumors, MS, syphilis
    • Biomarkers: e.g., amyloid beta, tau (Alzheimer risk) as applicable
  • Visual and microscopic assessment:
    • Record colour, clarity, volume for each tube
    • Traumatic tap vs hemorrhage: RBC distribution across tubes differs; traumatic tap shows decreasing RBCs from Tube 1 to Tube 4; if uniform RBCs across all tubes, suggests genuine hemorrhage
  • Common CSF analyses:
    • Routine chemistry: protein, glucose, lactate
    • Microbiology: Gram stain, culture; viral testing as indicated
    • Cytology and morphology: cytocentrifugation preferred for cell analysis
    • Hematology: total WBC count and differential; CSF usually 0–8×109/L in adults; higher counts with infection or inflammatory conditions
  • Cytocentrifugation (CSF):
    • Use specialized cytocentrifuge; slow spin improves cell yield and morphology
    • Procedure: mix ~0.5\,\text{mL} CSF with a few drops of bovine serum albumin; centrifuge slowly; transfer cells to slide; stain (e.g., Wright)
  • Smear preparation when cytocentrifuge unavailable: regular centrifuge; sediment onto slides; cells may be distorted
  • Routine CSF chemistry and microbiology highlights:
    • Protein increased with meningitis, hemorrhage, MS; glucose reduced in bacterial infection; levels should be measured promptly for glucose
    • Lactate used in meningitis evaluation
    • Biomarkers for CNS diseases and microbiology tests (Gram stain, culture, TB tests, VDRL for syphilis)

Serous Fluids

  • What they are: pleural (lungs), pericardial (heart), and peritoneal/ascitic (abdomen); normal appearance pale yellow; small volumes (pleural 1–10 mL typically)
  • Effusions: accumulation of serous fluid; differentiate transudates vs exudates
  • Transudates vs Exudates (key definitions):
    • Transudates: systemic factors altering pressure/filtration; e.g., CHF, liver dysfunction, nephrotic syndrome
    • Exudates: local inflammation or infection affecting membranes; e.g., infections, malignancy, inflammatory diseases
  • Differentiation criteria (fluid vs serum):
    • Fluid:serum protein ratio < 0.5 (transudate) or > 0.5 (exudate)
    • Fluid:serum LDH ratio < 0.6 (transudate) or > 0.6 (exudate)
    • WBC counts: < 1000/µL (transudate) vs > 1000/µL (exudate)
    • Spontaneous clotting: unlikely in transudates; may occur in exudates
    • Pleural fluid cholesterol ratio and bilirubin ratio help differentiation
    • Serum-ascites albumin gradient (SAAG): > 1.1 indicates transudate; < 1.1 indicates exudate
  • Pleural fluid testing significance:
    • Glucose: decreased in rheumatoid/inflammatory or purulent infection
    • Lactate: elevated with bacterial infection
    • Triglyceride: elevated in chylous effusions
    • ADA, Amylase: used for TB and other conditions or pancreatitis, respectively
  • Pericardial fluid: normal volume ~25 ext{--}50\,\text{mL}; testing includes Gram stain/culture, ADA for TB, cytology for malignant cells
  • Peritoneal fluid: normally < 100\,\text{mL} in cavity; turbid fluids indicate infection; TB may show lymphocyte predominance
  • Collection guidelines for serous fluids:
    • Typically 3 tubes: EDTA for cells and morphology; heparin for chemistry; sterile for Gram stain/culture
    • Optional additional tubes for cytology

Synovial Fluid

  • What it is: fluid within joints; viscous ultrafiltrate of plasma enriched with hyaluronate; hyaluronic acid gives normal viscosity
  • Normal characteristics: straw-colored, viscous; WBC < 200\,/\text{mL}; mostly mononuclear cells; sterile; crystals absent
  • Indications for arthrocentesis: diagnose joint disease (crystal-induced, degenerative, inflammatory, infectious)
  • Classification of joint fluid:
    • Noninflammatory (e.g., osteoarthritis, traumatic arthritis)
    • Inflammatory (e.g., RA, lupus arthritis)
    • Infectious (bacterial infection)
    • Crystal-induced (e.g., gout)
    • Hemorrhagic (bleeding in joint, tumor, trauma)
  • Collection and processing:
    • Three tubes: microbiology (sterile), liquid EDTA or heparin (microscopy), plain tube for clotting and chemistry/cytology
  • Routine examination:
    • Gross appearance, viscosity, WBC count, differential, and morphologic examination (cytocentrifuged slides preferred)
    • Microscopy for crystals
  • Microbiological testing: Gram stain and culture (bacteria, mycobacteria, fungi)
  • Chemistry tests: glucose (lower in infected joints), protein (increased in RA, gout, infections)
  • Other tests: LDH, uric acid, lactate; immunologic tests (RF, ANA)

Seminal Fluid

  • Context: semen analysis for fertility, forensic purposes, vasectomy assessment, ART suitability
  • Specimen handling:
    • Fresh specimen; ideally delivered within 30\,\text{minutes}; kept at 37^{\circ}\text{C}; examined within 2\ hours
    • Abstinence period: 3–5 days; avoid condom use prior to collection
    • Transport: keep warm if collected at home; prompt delivery to lab
  • Sperm count reference: 20\text{--}160\ times 10^6/\text{mL}
  • Macroscopic analysis: time to complete liquefaction, appearance, volume, viscosity, pH
  • Wet-mounted analysis: approximate sperm count and motility
  • Other assessments: viability, agglutination, counting-chamber counts, morphology on stained slides
  • Indications: fertility assessment, forensic purposes, vasectomy evaluation, ART suitability

Amniotic Fluid

  • Definition: nourishing, protective fetal liquid; clear, yellow, primarily water with proteins, carbohydrates, lipids, urea, electrolytes
  • Source: largely fetal urine in late gestation
  • Analysis: amniocentesis
  • Uses:
    • Fetal genetic cell analysis for defects
    • Chemical markers (e.g., fibronectin) to assess fetal lung maturity

Saliva

  • Characteristics: clear, alkaline, viscous; produced by salivary glands
  • Uses: microbial studies (viruses/bacteria), chemical tests (hormones, drugs, abused substances); blood group antigen secretor testing
  • Collection: typically chewed wax or dental cotton for several minutes

Human Chorionic Gonadotropin (hCG) – Beta Subunit (Pregnancy Testing)

  • What it is: pregnancy test targeting the beta subunit of hCG; also used as tumor marker in some cancers
  • Specimen type: urine (first-void preferred) or serum
  • Test types: qualitative (positive/negative) or quantitative (actual hCG concentration)
  • Rapid strips/cassette tests: high specificity (~98\%) for hCG
  • Principle: two lines indicate result; presence of test line with antibody–hCG reaction = positive
  • Procedure (urine/serum):
    • Remove strip from pouch; immerse in specimen without exceeding the max line
    • Place on a non-absorbent surface; start timer; read at ~3\, ext{min} (urine) or 5\, ext{min} (serum)
    • Interpret with trained personnel
  • Quality control for urine pregnancy tests:
    • External QC: test with positive and negative controls when opening a new box; document lot # and expiry; mark box as passed/ref passed
    • Internal QC: presence of T line (test) and C line (control) on each strip; if C line present and T line present => valid result; if only C line present or T line absent => invalid
  • Blood vs urine testing:
    • Advantages of blood: earlier detection (≈3–10 days post-conception); can measure concentration for monitoring
    • Disadvantages: more expensive, slower results, requires clinical lab

hCG – Beta Subunit: Procedure Details

  • Pregnancy tests by strips/cassette: qualitative urine/serum detection; 98% specificity
  • Reading results: based on appearance of lines after specified minutes
  • QC and interpretation emphasize external and internal controls

Body Fluid Retention, Storage, and Disposal

  • Retention and storage:
    • Refrigerate most body fluids unless SOP specifies otherwise
    • Retention times vary by specimen type (roughly 48 hours to 7 days depending on fluid and tests)
  • Disposal:
    • Use leak-proof, tear-resistant biohazard bags/containers; clearly labeled with biohazard symbol
    • Ensure containers are sealed to prevent leakage

Quick reference values and concepts (summary)

  • CSF normal adult volume: 90\text{--}150\,\text{mL}; protein ~35\,\text{mg/dL}; glucose ~60\,\text{mg/dL}; WBC count ~0--8\times 10^9/\text{L} in adults
  • Fluid/serum tests differentiate transudates vs exudates using protein LDH ratios, WBC counts, and SAAG
  • Synovial fluid normal WBCs: < 200\,/\text{mL}; crystals absent; high viscosity due to hyaluronate
  • Sperm count reference: 20--160\times 10^6/\text{mL}
  • Amniotic fluid used for fetal genetic and maturational markers
  • hCG testing: qualitative or quantitative; strip tests provide rapid results; QC essential