Pleural Fluid Analysis

Pleural Fluid Analysis

Synonym/acronym: Thoracentesis fluid analysis.

Common use

To assess and categorize fluid obtained from within the pleural space for infection, cancer, and blood as well as identify the cause of its accumulation.


Pleural fluid (5 mL) collected in a green-top (heparin) tube for amylase, cholesterol, glucose, lactate dehydrogenase (LDH), pH, protein, and triglycerides; lavender-top (EDTA) tube for cell count; sterile containers for microbiology specimens; 200 to 500 mL of fluid in a clear container with anticoagulant for cytology. Ensure that there is an equal amount of fixative and fluid in the container for cytology.

Normal findings

(Method: Spectrophotometry for amylase, cholesterol, glucose, LDH, protein, and triglycerides; ion-selective electrode for pH; automated or manual cell count; macroscopic and microscopic examination of cultured microorganisms; microscopic examination of specimen for microbiology and cytology)
ColorPale yellow
AmylaseParallels serum values
CholesterolParallels serum values
CEAParallels serum values
GlucoseParallels serum values
LDHLess than 200 units/L
Fluid LDH-to-serum LDH ratio0.6 or less
Protein3 g/dL
Fluid protein-to-serum protein ratio0.5 or less
TriglyceridesParallel serum values
RBC countNone seen
WBC countLess than 1,000/microL
CultureNo growth
Gram stainNo organisms seen
CytologyNo abnormal cells seen
CEA = carcinoembryonic antigen; LDH = lactate dehydrogenase; RBC = red blood cell; WBC = white blood cell.


The pleural cavity and organs within it are lined with a protective membrane. The fluid between the membranes is called serous fluid. Normally, only a small amount of fluid is present because the rates of fluid production and absorption are about the same. Many abnormal conditions can result in the buildup of fluid within the pleural cavity. Specific tests are usually ordered in addition to a common battery of tests used to distinguish a transudate from an exudate. Transudates are effusions that form as a result of a systemic disorder that disrupts the regulation of fluid balance, such as a suspected perforation. Exudates are caused by conditions involving the tissue of the membrane itself, such as an infection or malignancy. Fluid is withdrawn from the pleural cavity by needle aspiration and tested as listed in the previous and following tables.
AppearanceClearCloudy or turbid
Specific gravityLess than 1.015Greater than 1.015
Total proteinLess than 2.5 g/dLGreater than 3 g/dL
Fluid protein-to-serum protein ratioLess than 0.5Greater than 0.5
LDHParallels serum valueLess than 200 units/L
Fluid LDH-to-serum LDH ratioLess than 0.6Greater than 0.6
Fluid cholesterolLess than 55 mg/dLGreater than 55 mg/dL
WBC countLess than 100/microLGreater than 1,000/microL
LDH = lactate dehydrogenase; WBC = white blood cell.

This procedure is contraindicated for



  • Differentiate transudates from exudates
  • Evaluate effusion of unknown cause
  • Investigate suspected rupture, immune disease, malignancy, or infection

Potential diagnosis

Bacterial or tuberculous empyema: Elevated white blood cell (WBC) count with a predominance of neutrophils, increased fluid protein-to-serum protein ratio, increased fluid LDH-to-serum LDH ratio, decreased glucose, pH less than 7.3 Chylous pleural effusion: Marked increase in both triglycerides (two to three times serum level) and chylomicrons Effusion caused by pneumonia: Elevated WBC count with a predominance of neutrophils and some eosinophils, increased fluid protein-to-serum protein ratio, increased fluid LDH-to-serum LDH ratio, pH less than 7.4 (and decreased glucose if bacterial pneumonia) Esophageal rupture: Significantly decreased pH (6.0) and elevated amylase Hemothorax: Bloody appearance, increased RBC count, elevated hematocrit Malignancy: Elevated WBC count with a predominance of lymphocytes, possible elevated RBC count, abnormal cytology, increased fluid protein-to-serum protein ratio, increased fluid LDH-to-serum LDH ratio, decreased glucose, pH less than 7.3 Pancreatitis: Elevated WBC count with a predominance of neutrophils, elevated RBC count, pH greater than 7.3, increased fluid protein-to-serum protein ratio, increased fluid LDH-to-serum LDH ratio, increased amylase Pulmonary infarction: Elevated RBC count, elevated WBC count with a predominance of neutrophils, pH greater than 7.3, normal glucose, increased fluid protein-to-serum protein ratio, and increased fluid LDH-to-serum LDH ratio. Pulmonary tuberculosis: Elevated WBC count with a predominance of lymphocytes, positive acid-fast bacillus stain and culture, increased protein, decreased glucose, pH less than 7.3 Rheumatoid disease: Elevated WBC count with a predominance of either lymphocytes or neutrophils, pH less than 7.3, decreased glucose, increased fluid protein-to-serum protein ratio, increased fluid LDH-to-serum LDH ratio, increased immunoglobulins Systemic lupus erythematosus: Similar findings as with rheumatoid disease, except that glucose is usually not decreased

Critical findings

  • Positive culture findings in any sterile body fluid.

  • Note and immediately report to the health-care provider (HCP) positive culture results, if ordered, and related symptoms. pH 7.1 to 7.2 indicates need for immediate drainage.

  • It is essential that a critical finding be communicated immediately to the requesting health-care provider (HCP). A listing of these findings varies among facilities.

  • Timely notification of a critical finding for lab or diagnostic studies is a role expectation of the professional nurse. Notification processes will vary among facilities. Upon receipt of the critical value the information should be read back to the caller to verify accuracy. Most policies require immediate notification of the primary HCP, Hospitalist, or on-call HCP. Reported information includes the patient’s name, unique identifiers, critical value, name of the person giving the report, and name of the person receiving the report. Documentation of notification should be made in the medical record with the name of the HCP notified, time and date of notification, and any orders received. Any delay in a timely report of a critical finding may require completion of a notification form with review by Risk Management.

Interfering factors

  • Bloody fluids may be the result of a traumatic tap.
  • Unknown hyperglycemia or hypoglycemia may be misleading in the comparison of fluid and serum glucose levels. Therefore, it is advisable to collect comparative serum samples a few hours before performing thoracentesis.

Nursing Implications and Procedure


  • Positively identify the patient using at least two unique identifiers before providing care, treatment, or services.
  • Patient Teaching: Inform the patient this test can assist in identifying the type of fluid being produced within the body cavity.
  • Obtain a history of the patient’s complaints, including a list of known allergens, especially allergies or sensitivities to latex.
  • Obtain a history of the patient’s immune and respiratory systems, especially any bleeding disorders and other symptoms, as well as results of previously performed laboratory tests and diagnostic and surgical procedures.
  • Note any recent procedures that can interfere with test results.
  • Record the date of the last menstrual period and determine the possibility of pregnancy in perimenopausal women.
  • Obtain a list of the patient’s current medications, including anticoagulants, aspirin and other salicylates, herbs, nutritional supplements, and nutraceuticals (see Effects of Natural Products on Laboratory Values online at DavisPlus). Such products should be discontinued by medical direction for the appropriate number of days prior to a surgical procedure.
  • Review the procedure with the patient. Inform the patient that it may be necessary to remove hair from the site before the procedure. Discuss with the patient that the requesting HCP may request that a cough suppressant be given before the thoracentesis. Address concerns about pain and explain that a sedative and/or analgesia will be administered to promote relaxation and reduce discomfort prior to needle insertion through the chest wall into the pleural space. Explain that any discomfort with the needle insertion will be minimized with local anesthetics and systemic analgesics. Explain that the local anesthetic injection may cause an initial stinging sensation. Meperidine (Demerol) or morphine may be given as a sedative. Inform the patient that the needle insertion is performed under sterile conditions by an HCP specializing in this procedure. The procedure usually takes about 20 min to complete.
  • Explain that an IV line will be inserted to allow infusion of IV fluids, antibiotics, anesthetics, and analgesics.
  • Sensitivity to social and cultural issues, as well as concern for modesty, is important in providing psychological support before, during, and after the procedure.
  • Note that there are no food or fluid restrictions unless by medical direction. The requesting HCP may request that anticoagulants and aspirin be withheld. The number of days to withhold medication is dependent on the type of anticoagulant.
  • Make sure a written and informed consent has been signed prior to the procedure and before administering any medications.


  • Potential complications:
  • Pneumothorax, bleeding, hemoptysis, and pulmonary edema.

  • Ensure that anticoagulant therapy has been withheld for the appropriate number of days prior to the procedure. Notify the HCP if patient anticoagulant therapy has not been withheld.
  • Have emergency equipment readily available. Keep resuscitation equipment on hand in the case of respiratory impairment or laryngospasm after the procedure.
  • Avoid using morphine sulfate in those with asthma or other pulmonary disease. This drug can further exacerbate bronchospasms and respiratory impairment.
  • Have the patient remove clothing and change into a gown for the procedure.
  • Instruct the patient to cooperate fully and to follow directions. Direct the patient to breathe normally and to avoid unnecessary movement during the local anesthetic and the procedure.
  • Observe standard precautions, and follow the general guidelines in Patient Preparation and Specimen Collection. Positively identify the patient, and label the appropriate specimen container with the corresponding patient demographics, initials of the person collecting the specimen, date and time of collection, and site location.
  • Record baseline vital signs and continue to monitor throughout the procedure. Protocols may vary among facilities.
  • Establish an IV line to allow infusion of IV fluids, anesthetics, analgesics, or IV sedation.
  • Assist the patient into a comfortable sitting or side-lying position.
  • Prior to the administration of local anesthesia, clip hair from the site as needed, cleanse the site with an antiseptic solution, and drape the area with sterile towels. The skin at the injection site is then anesthetized.
  • The thoracentesis needle is inserted, and fluid is removed.
  • The needle is withdrawn, and pressure is applied to the site with a petroleum jelly gauze. A pressure dressing is applied over the petroleum jelly gauze.
  • Monitor the patient for complications related to the procedure (e.g., allergic reaction, anaphylaxis).
  • Place samples in properly labeled specimen container, and promptly transport the specimen to the laboratory for processing and analysis.


  • Inform the patient that a report of the results will be made available to the requesting HCP, who will discuss the results with the patient.
  • Instruct the patient to resume usual medications, as directed by the HCP.
  • Monitor vital signs every 15 min for the first hr, every 30 min for the next 2 hr, every hour for the next 4 hr, and every 4 hr for the next 24 hr. Take the patient’s temperature every 4 hr for 24 hr. Monitor intake and output for 24 hr. Notify the HCP if temperature is elevated. Protocols may vary among facilities.
  • Observe/assess the patient for signs of respiratory distress or skin color changes.
  • Observe/assess the thoracentesis site for bleeding, inflammation, or hematoma formation each time vital signs are taken and daily thereafter for several days.
  • Observe/assess the patient for hemoptysis, difficulty breathing, cough, air hunger, pain, or absent breathing sounds over the affected area. Report to HCP.
  • Inform the patient that 1 hr or more of bed rest (lying on the unaffected side) is required after the procedure. Elevate the patient’s head for comfort.
  • Evaluate the patient for symptoms indicating the development of pneumothorax, such as dyspnea, tachypnea, anxiety, decreased breathing sounds, or restlessness. Prepare the patient for a chest x-ray, if ordered, to ensure that a pneumothorax has not occurred as a result of the procedure.
  • Observe/assess for nausea and pain. Administer antiemetic and analgesic medications as needed and as directed by the HCP.
  • Administer antibiotics, as ordered, and instruct the patient in the importance of completing the entire course of antibiotic therapy even if no symptoms are present.
  • Recognize anxiety related to test results, and offer support. Discuss the implications of abnormal test results on the patient’s lifestyle. Provide teaching and information regarding the clinical implications of the test results, as appropriate. Educate the patient regarding access to counseling services, if appropriate.
  • Reinforce information given by the patient’s HCP regarding further testing, treatment, or referral to another HCP. Answer any questions or address any concerns voiced by the patient or family.
  • Depending on the results of this procedure, additional testing may be performed to evaluate or monitor progression of the disease process and determine the need for a change in therapy. Evaluate test results in relation to the patient’s symptoms and other tests performed.

Related Monographs

  • Related tests include antibodies anti-cyclic citrullinated peptide, ANA, biopsy lung, blood gases, cancer antigens, chest x-ray, CBC WBC count and differential, CT thoracic, CRP, culture and smear mycobacteria, culture blood, culture fungal, culture viral, ECG, ESR, MRI chest, and RF.
  • Refer to the Immune and Respiratory systems tables at the end of the book for related tests by body system.
Handbook of Laboratory and Diagnostic Tests, © 2013 Farlex and Partners
References in periodicals archive ?
Pleural fluid analysis was consistent with an acidic, transudative effusion with a pleural fluid/serum creatinine ratio of 1.3.
We retrospectively identified and included all known cases of MPE, defined as malignant cells present on pleural fluid analysis or pleural biopsy, that were managed at our institution from January 2014 to December 2016.
Diagnosing tuberculous pleural effusion using clinical data and pleural fluid analysis: a study of patients less than 40 years-old in an area with a high incidence of tuberculosis.
Pleural fluid analysis was as follows: hematocrit (Hct) 22%, red blood cells (RBC) 126,000/mm3, white blood cells (WBC) 1,400/mm3; bacterial gram-stain, culture, and acid-fast bacilli smear were negative for bacteria and tuberculosis, respectively, and cytology negative for malignant cells.
Hence, we carried out this study with an objective of highlighting the importance of pleural fluid ADA plus basic pleural fluid analysis in form of routine and microscopy examination in evaluating a case of tuberculous pleural effusion.
Thoracentesis was performed and pleural fluid analysis revealed a transudative fluid consistent with hepatic hydrothorax.
Pleural fluid analysis showed a predominance of lymphocytes (90%) and a lactate dehydrogenase level of 120 U/L, glucose of 157 mg/dL, protein of 4.8 g/dL, amylase of 39 U/L, and triglycerides of 405 mg/dL.
In cases with an unclear etiology, diagnostic thoracentesis with pleural fluid analysis is the gold standard test.
Getting the mostfrom pleural fluid analysis. Review.
Even if radiography is an effective way to identify a pleural effusion, advance imaging, pleural fluid analysis and when applicable pleural biopsy are key elements to uncover the aetiology of the underlying disease.