Cerebrospinal, Synovial, and Serous Body Fluids

Indication

• Appropriate laboratory examination of these fluids is critical for the diagnosis of numerous diseases– (i.e., bacterial, viral and fungal infections;

distinction between various arthritides; primary [i.e., mesothelioma ] and metastatic malignancies; among others).

• Accurate test interpretation depends on appropriate specimen collection, turnaround time, physician/laboratory communication, and reliable reference values.

Cerebrospinal Fluid

• In adults, approximately 500 mL of cerebrospinal fluid (CSF)is produced each day (0.3-0.4 mL/min).

• The total adult volume varies from 90-150 mL,– about 25 mL of which is in the ventricles and the

remainder in the subarachnoid space.• In neonates, the volume varies from 10-60 mL. • The total CSF volume is replaced every 5-7

hours

CSF functions

• Several major functions:• (a) it provides physical support since the 1500

g brain weighs about 50 g when suspended in CSF;

• (b) it confers a protective effect against sudden changes in acute venous (respiratory and postural) and arterial blood pressure or impact pressure;

CSF functions

• (c) it provides an excretory waste function since the brain has no Iymphalic system;

• (d) it is the pathway whereby hypothalamus releasing factors are transported to the cells of the median eminence;

• (e) it maintains central nervous system ionic homeostasis .

BBB

• The blood-brain barrier – It consists of two morphologically distinct

components:– a unique capillary endothelium held together by intercellular

tight junctions,&

– the choroid plexus, where a single layer of specialized choroidal ependyma cells connected by tight junctions overlies fenestrated capillaries.

• The CSF ionic components– (e.g., H+, K+, Ca2+, Mg2+,bicarbonate, etc.) are tightly

regulated by specific transport systems,• Glucose, urea, and creatinine diffuse freely but

require 2 or more hours to equilibrate.

• Proteins cross by passive diffusion at a rate dependent on the plasma-to-CSF concentration gradient and inversely proportional to their molecular weight and hydrodynamic volume

• the BBB maintains the relative homeostasis of the central nervous system environment during acute perturbations of plasma components.

Specimen Collection

• Cerebrospinal fluid may be obtained by lumbar puncture

• Up to 20 mL of CSF may normally be removed• the clinician should be aware of the clinical

history • The sample site (i.e., lumbar, cisternal, etc.)

should be noted since cytologic and chemical parameters vary at different sites

• The necessity for a simultaneous serum glucose should also be considered. This is best obtained 2-4 hours before lumbar puncture because of the delay in serum-CSF equilibrium.

• The CSF specimen is usually divided into three serially collected sterile tubes:– tube 1 for chemistry and immunology studies;– tube 2 for microbiologic examination; – tube 3 for cell count and differential.

• if tube 1 is hemorrhagic due to a traumatic puncture, it should not be used when protein studies are the most important aspect of the analysis (i.e., suspected multiple sclerosis).

• Glass tubes should be avoided • Specimens should be delivered to the

laboratory and processed quickly to minimize cellular degradation (<1 h)

• Refrigeration is contraindicated for culture Specimens– because fastidious organisms (e.g., Haemophilus

influenzae and Neisseria meningitidis) will not survive.

Indications and Recommended Tests

• four major disease categories:– Meningeal infection, subarachnoid hemorrhage,

primary or metastatic malignancy, and demyelinating diseases

• Identification of infectious meningitis, particularly bacterial, is the most important indication for CSF examination

Diseases Detected by Laboratory Examination of CSF

• CSF examination for other diseases– often provides supportive evidence of a clinical

diagnosis or helps to rule out other diseases.

Recommended CSF Laboratory Tests

Gross Examination

• Normal CSF is crystal clear and colorless and has a viscosity similar to that of water.

• Turbidity or cloudiness– leukocyte (WBC) counts over 200 cells/μL – red cell (RBC) counts of 400/ μL. However, grossly bloody

fluids have RBC counts greater than 6000/ μL. – Microorganisms (bacteria, fungi, amebas),– Radiographic contrast material,– Aspirated epidural fat– Protein level greater than 150 mg/dL (1.5 g/L)

Xanthochromia and Associated Diseases/Disorders

• Xanthochromia– To detect xanthochromia, the CSF should be

centrifuged and the supernatant fluid compared with a tube of distilled water.

– Xanthochromic CSF is pink, orange, or yellow owing to RBC lysis and hemoglobin breakdown.

• Differential Diagnosis of Bloody CSF– Distinction of a traumatic puncture from

pathologic hemorrhage – In a traumatic tap, the hemorrhagic fluid usually

clears between the first and third collected tubes, but remains relatively uniform in subarachnoid hemorrhage.

– Xanthochromia, microscopic evidence of erythrophagocytosis, or hemosiderin-laden macrophages indicate a subarachnoid bleed

Microscopic Examination

• Total Cell Count

• The normal leukocyte cell count– adults , 0-5 cells/μL.– It is higher in neonates, ranging from 0-30 cells/μL.

with the upper limit of normal decreasing to adult values by adolescence.

• No RBCs should be present in normal CSF.• If numerous (except a traumatic tap), a

pathologic process is probable (e.g., trauma, malignancy, infarct, hemorrhage).

• Red cell counts have limited diagnostic value, they may give a useful approximation of the true CSF white blood count (WBC) or total protein in the presence of a traumatic puncture by correcting for leukocytes or protein introduced by the traumatic puncture.

• In the presence of a normal peripheral blood RBC count and serum protein, these corrections amount to about 1 WBC for every 700 RBCs and 8 mg/dL protein for every 10 000 RBC/μL.

• Differential Cell Count– Wright's staining of air-dried cytospins. Indeed, it

is the recommended method for differential cell counts in all body fluids

Causes of Increased CSF Neutrophils

Causes of CSF Lymphocytosis

Chemical AnalysisAdult Lumbar CSF Reference Values

Proteins

• Over 80% of the CSF protein content is derived from blood plasma, in concentrations of less than 1% of the plasma level

• it is the most common abnormality found in CSF.

• an increased CSF protein serves as a useful, albeit nonspecific, indicator of meningeal or CNS disease.

Mean Concentrations of Plasma and CSF Proteins

• infants have significantly higher CSF protein levels than older children and adults.

Conditions Associated with Increased CSF Total Protein

CSF Proteins and Central Nervous System Diseases

Glucose

• fasting CSF glucose levels are normally 50-80 mg/dL(2.8-4.4 mmol/L), about 60% of plasma values

• The normal CSF/plasma glucose ratio varies from 0.3-0.9

• CSF values below 40 mg/dL (2.2 mmol/L) or ratios below 0.3 are considered to be abnormal.

• Hypoglycorrhachia is a characteristic finding of bacterial, tuberculous, and fungal meningitis. However, sensitivity can be as low as 55% for bacterial meningitis

• Decreased CSF glucose results from increased anaerobic glycolysis in brain tissue and leukocytes and impaired transport into the CSF.

• CSF glucose levels normalize before protein levels and cell counts during recovery from meningitis, making it a useful parameter in assessing response to treatment.

• Increased CSF glucose is of no clinical ignificance, reflecting increased blood glucose levels within 2 hours of lumbar puncture. A traumatic tap may also cause a spurious increase in CSF glucose.

Typical Lumbar CSF Findings in Meningitis

Microbiological Examination

• A thorough and prompt examination of cerebrospinal fluid is essential for the diagnosis of CNS infection because an inaccurate or delayed report may result in significant mortality or morbidity. Although changes in opening pressure, total cell and differential counts, total protein, and glucose suggest an infectious etiology, Gram stain and culture are critical for a definitive diagnosis.

• The most common agents of bacterial meningitis• are group B streptococcus (neonates), Neisseria

meningitidis (3 months and older) ,Streptococcus pneumoniae (3 months and older), Escherichia coli and other Gram.negative bacilli (newborn to 1 month),Haemophilm influenzae (3 months to 18 years) and Listeria monocyLDgenes

• (neonates, elderly, alcoholics, & immunosuppressed)

Synovial Fluid

• (SF)– an imperfect ultrafiltrate of blood plasma combined with

hyaluronic acid produced by the synovial cells.• Small ions and molecules (e.g., Na+, K+, glucose, urea,

etc.) readily pass into the joint space and are, therefore, similar in concentration to plasma,

• Large molecules– absent or present in trace amounts. Resorption of synovial

molecules is by the lymphatics and is not size dependent. • SF acts as a lubricant and adhesive, and provides

nutrients for the avascular articular cartilage.

Examination of the synovial fluid

• is essential to– Distinguish infectious from noninfectious arthritis.

• Gross and microscopic examination• Gram stain, culture, and crystal examination• Synovial fluid parameters can be nonspecific

and must be integrated into the clinical context.

Synovial Fluid Findings by Disease Category

Specimen Collection

• Synovial fluid must be collected with sterile, disposable needles and plastic syringes to avoid contamination by birefringent particulates. The syringe may be heparinized with 25 U of sodium heparin/mL of SF in routine arthrocentesis.

• Oxalate, lithium heparin, and powdered ethylenediaminetetraacetic acid (EDTA) anticoagulants should be avoided because they form crystal artifacts that may be misleading during the microscopic examination.

• Prior to aspiration, turn or manipulate the joint to ensure mixing of its contents.

Specimen Collection

• The specimen should ideally be separated into three parts:– 3-10 mL into a sterile heparinized tube or syringe

for microbiological studies;– 2-5 mL in an anticoagulant tube (sodium heparin

or liquid EDTA) for microscopic examination;– about 5 mL into a plain (no anticoagulant) tube for

chemical analysis (normal synovial fluid does not clot since fibrinogen is absent).

Recommended Tests

Crystals

• Monosodium urate• Calcium pyrophosphllte dihydrate• Calcium Hydroxyapatites• Calcium oxalate dihydrare • Lipid crystals • Crystalline corticosteroids • Cholesterol crystals

Reference Intervals for Synovial Fluid Constituents