Pleural fluid

Zar shad
 Pleural fluid
• Pleural fluid is the fluid that is found between the
layers of the pleura, the membranes that line the
thoracic cavity and surround the lungs.

• The space containing the pleural fluid is referred to

as the pleural cavity.

• Normal pleural fluid consists of a small amount of a

thin (serous) fluid that functions as a lubricant
during breathing.
 Pleural effusion
• An excess amount of pleural fluid is known as
a pleural effusion.

• Pleural effusion develops when more fluid

enters the pleural space than is removed.
 Mechanisms
Potential mechanisms of fluid increased interstitial fluid in the
lungs secondary to

• increased pulmonary capillary pressure (i.e., heart failure) or

permeability (i.e., pneumonia)
• decreased intrapleural pressure (i.e., atelectasis)
• decreased plasma oncotic pressure (i.e.,hypoalbuminemia)
• increased pleural membrane permeability and obstructed
lymphatic flow (e.g., pleural malignancy or infection)
• diaphragmatic defects (i.e., hepatic hydrothorax)
• thoracic duct rupture (i.e., chylothorax).
 Initial Evaluation
• The history and physical examination are
critical in guiding the evaluation of pleural
effusion.
• Signs and symptoms of an effusion vary
depending on the underlying disease, but
dyspnea, cough, and pleuritic chest pain are
common.
• History:
Abdominal surgical procedures, Alcohol abuse or
pancreatic disease, Asbestos exposure, Cancer, Cardiac
surgery or myocardial injury, Childbirth, HIV, RA, SLE
etc.
• Sign:
Ascites, Dyspnea on exertion, orthopnea, Unilateral
lower extremity swelling, Yellowish nails etc.
• Symptoms:
Fever, Hemoptysis, Weight loss
 Chest radiographs
• Posteroanterior and lateral chest radiographs usually
confirm the presence of a pleural effusion.
• Ultrasound or computed tomography (CT) scans are
definitive for detecting small effusions and for
differentiating pleural fluid from pleural thickening.

Posteroanterior radiograph demonstrating blunting of the left costophrenic

angle
 Thoracentesis
• A procedure called thoracentesis is used to get a
sample of pleural fluid.

• Except for patients with obvious heart failure,

thoracentesis should be performed in all patients with
more than a minimal pleural effusion (i.e., larger than
1 cm height on lateral decubitus radiograph,
ultrasound, or CT) of unknown origin.
 Pleural fluid analysis
Observing the gross appearance of the pleural fluid may
suggest a particular cause.
Pleural fluid Test indicated Interpretation
Bloody Haematocrit Comparison to serum
Haematocrit
<1% – non-significant
1-20% – Cancer,
trauma, pneumonia
>50% – Haemothorax

Cloudy or turbid Triglycerides >110mg/dL-

chylothorax
 Pleural fluid analysis

• Pleural effusions are either transudates or exudates

based on the biochemical characteristics of the fluid,
which usually reflect the physiologic mechanism of
its formation.
 Transudate
• Transudate is extravascular fluid with low protein
content and a low specific gravity (< 1.012).

• It has low nucleated cell counts (less than 500 to

1000 /microlit) and the primary cell types are
mononuclear cells: macrophages, lymphocytes and
mesothelial cells.

• Transudates result from imbalances in hydrostatic and

oncotic forces.
 Transudate
• caused by a limited number of recognized clinical
conditions such as heart failure and cirrhosis.

• Less common causes include nephrotic syndrome,

atelectasis, peritoneal dialysis, constrictive
pericarditis, superior vena caval obstruction, and
urinothorax.

• Transudative effusions usually respond to treatment

of the underlying condition (e.g., diuretic therapy).
 Exudate
• A fluid with a high content of protein and cellar debris t
hat has escaped from blood vessels and has been deposi
ted in tissues or on tissue
surfaces, usually as a result of inflammation.

• It can be a pus-like or clear fluid.

• The fluid is composed of serum, fibrin, and white blood

cells.
 Exudate
• Exudates occur when the local factors
influencing the accumulation of pleural fluid
are altered.

• Pneumonia, malignancy, and

thromboembolism account for most exudative
effusions.
 Light’s criteria
• In clinical practice, exudative effusions can be
separated effectively from transudative effusions
using Light’s criteria.

• Fluid is exudate if it meets 1 of 3 criteria:

1. Pleural fluid LDH/serum LDH > 0.6
2. Pleural fluid protein/serum protein > 0.5
3. Pleural fluid LDH > 2/3 of upper limit of normal
serum LDH.
• If all 3 negative, fluid is Transudate
 Additional criteria
Confirm transudative exudate if results
equivocal
• Serum protein – pleural fluid protein >3.1 g/dL
• Serum albumin – pleural fluid albumin <1.2g/dL

However, neither protein nor albumin gradients alone

should be the primary test used to distinguish
transudative effusions from exudative effusions.
 Estimation of Globulins
• Test performed on serous fluids is Rivalta test.

• Required reagent is prepared by adding one

drop of glacial acetic acid to 100 ml of distilled
water in a conical flask.

• To this added 1-2 drops of centrifuged

supernatant fluid.
 Interpretation of test
• No cloud Normal fluid

• Faint cloud Transudate

• Distinct cloud Exudate

 Differences in exudate and transudate
Measurement Transudate Exudate†

Protein (g/dL) <3.0 >3.0

Fluid/serum ratio <0.5 ≥0.5

LDH (IU) <200 ≥200

Fluid/serum ratio <0.6 ≥0.6

WBCs‡ <10,000/µL >10,000/µL

RBCs <5000 >5000

Glucose >40 <40

pH >7.2 <7.2
 FURTHER TESTING FOR EXUDATES

Following pleural fluid tests should be performed on

fluid obtained during the initial thoracentesis:
• cell counts and differential
• glucose
• adenosine deaminase (ADA)
• cytologic analysis
• Bacterial cultures and pH should be tested if
infection is a concern.
 cell counts and differential

• Pleural fluid for total white blood cell (WBC) count

and differential cell count should be sent in an
anticoagulated tube.

• The predominant WBC population is determined by

the mechanism of pleural injury and the timing of the
thoracentesis in relation to the onset of the injury.
 Routine Pleural Fluid Tests for Pleural Effusion

SUGGESTED
TEST TEST VALUE DIAGNOSIS
Adenosine deaminase > 40 U per L Tuberculosis (> 90
(ADA) percent), empyema
(60 percent),
complicated
parapneumonic
effusion (30 percent),
malignancy (5
percent), rheumatoid
arthritis
Cytology Present Malignancy
Glucose < 60 mg per dL (3.3 Complicated
mmol per L) parapneumonic
effusion or empyema,
tuberculosis (20
percent), malignancy
(< 10 percent),
 Routine Pleural Fluid Tests for Pleural Effusion

SUGGESTED
TEST TEST VALUE DIAGNOSIS
Lactate > Two thirds of upper Any condition causing
dehydrogenase (LDH) limits of normal for an exudate
serum LDH
LDH fluid to serum > 0.6 Any condition causing
ratio an exudate
Protein fluid to serum > 0.5 Any condition causing
ratio an exudate
Red blood cell count > 100,000 per Malignancy, trauma,
mm3(100 × 106 per L) parapneumonic
effusion, pulmonary
embolism
White blood cell count > 10,000 per mm3(10 Empyema, other
and differential ×3 109 per L) exudates
(uncommon)
 Routine Pleural Fluid Tests for Pleural Effusion

SUGGESTED
TEST TEST VALUE DIAGNOSIS
Eosinophils > 10 percent Pneumothorax,
haemothorax,
asbestosis,
Lymphocytes > 50 percent Malignancy,
tuberculosis,
pulmonary embolism,
coronary artery
bypass surgery
Neutrophils > 50 percent Parapneumonic
effusion, pulmonary
embolism, abdominal
diseases
 PH testing
• Pleural fluid for pH testing should be collected anaerobically in a
heparinized syringe and measured in a blood-gas machine.

• The pH of normal pleural fluid is 7.64.

• A low pleural fluid pH value has prognostic and therapeutic implications

for patients with parapneumonic and malignant pleural effusions.

• A pH of <6.0 is highly suggestive of oesophageal rupture.

• <7.20 with pneumonia…Drain the fluid

• <7.30 with malignancy …Life expectancy 30 days
 Glucose
• When a pleural fluid pH value is not available,
a pleural fluid glucose concentration less than
60 mg per dL can be used to identify
complicated parapneumonic effusions.
Optional Pleural Fluid Tests for Pleural Effusion

SUGGESTED
TEST TEST VALUE DIAGNOSIS
Amylase > Upper limit of Malignancy (<20
normal percent), pancreatic
disease, esophageal
rupture
Cholesterol > 45 to 60 mg per dL Any condition causing
an exudate
Culture Positive Infection
Hematocrit fluid to ≥0.5 Hemothorax
blood ratio
Interferon* Different cutoff points Tuberculosis
Polymerase chain Positive Infection
reaction †
Optional Pleural Fluid Tests for Pleural Effusion

SUGGESTED
TEST TEST VALUE DIAGNOSIS
Triglycerides > 110 mg per dL Chylothorax
(1.24 mmol per L)
Tumor markers‡ Different cutoff points Malignancy
 Test for Viscosity
• Aspirate fluid in a pipette and then release.

• If falling drop draws into a band of 5 cm or

long the viscosity is normal.

• If length of band is less than 5 cm viscosity is

decreased.
 Microscopic examination
• Gram Smear:
Look for pus cells and bacteria
• Ziehl-Neelsen
Look for AFB
• Cytology smear
When malignancy is suspected
• Wet prepration:
for Crystals and Inclusions
 Wet prepration
• A drop of fluid is placed on a clean slide and covered
lightly with cover slip.

• Examined under microscope.

• Needle-like crystals of urates gouty arthritis

• small, multiple, dark inclusions in polymorphs
RA