Fluid Analysis Guidelines

Only the fluid types below and specific analyses tabled are now allowable in Telepath and ICE. Where a fluid type or analysis is not allowable in Telepath please book as miscellaneous and then contact the Duty Biochemist before analysis is performed.

All fluids must be centrifuged and then analysed only if free from particles.


Fluid type

Clinical Indication

Analyses available



Pleural Fluid

Four types of fluids can accumulate in the pleural space:

  • Serous fluid (hydrothorax)
  • Blood (haemothorax)
  • Chyle (chylothorax)
  • Pus (pyothorax or empyema)


 ? transudate or exudates


A transudate fluid is produced through pressure filtration without capillary injury while exudate is "inflammatory fluid" leaking between cells.

Most common causes of pleural exudates are bacterial pneumonia and malignancy.

Most common causes of pleural transudates are left ventricular failure and cirrhosis.

Protein, LDH

(measure serum protein and LDH simultaneously)

TP <25g/L indicates transudate

TP>35g/L indicates exudate

Light’s criteria applies to pleural fluid TP between 25 and 35g/L.

A fluid is an exudate if any of the following apply:

Ratio of fluid protein to serum protein is >0.5

Ratio of fluid LDH to serum LDH is >0.6

Pleural fluid LDH is > 2/3rds the upper reference limit for plasma LDH.

? infected


pH should be collected anaerobically with heparin and then measured in a blood gas analyser using a clot filter.

? chylothorax

Cholesterol,  Triglyceride

If still cloudy after centrifugation, visual inspection for chylomicrons may be required. Contact DB.

? pancreatitis


Patient's serum amylase should be measured for comparison.

? rheumatic cause


Fluoride oxalate tube required.


Ascitic Fluid





? cirrhotic or malignant

Albumin, LDH, Cholesterol

Serum albumin should be simultaneously measured for comparison



pH, Protein

For rare instances pH should be collected anaerobically with heparin and then measured in a blood gas analyser using clot filter.

? tubercular


Fluoride oxalate tube required.

? pancreatic fistula


Serum amylase should be measured


Drain Fluid

? contains urine

Urea, creatinine

Comparison of fluid urea and creatinine with serum will identify significant contamination with urine

Post surgery

Amylase, bilirubin



? bacterial meningitis

Protein, glucose, lactate

Glucose & lactate needs fluoride oxalate tube

? Subarachnoid haemorrhage

CSF blilirubin, oxhaemoglobin (measured by spectrophotometer)

Total protein

Serum total protein and bilirubin should be measured simultaneously


Chest Drain Fluid

? chylothorax

Cholesterol, Triglyceride

If still cloudy after centrifugation, visual inspection for chylomicrons may be required. Contact DB.


Gastric Aspirate

? reflux, ?achlorhydria


Occasionally gastric pH may be requested in patients suspected of intestinal reflux or achlorhydria. Normally the fasting gastric pH is about 1-2. Analyse by lab pH meter.


Nasal Fluid


Tau protein

Dispatch to specialist referral centre.


Pancreatic Cyst Fluid

? Ca pancreas

CEA, CA 19-9



  1. BTS guidelines for the investigation of a unilateral pleural effusion in adults, Maskell N A et al. Thorax 2003; 58(Suppl II):ii8-ii17
  2. BTS guidelines for the management of pleural infection, Davies C W H et al. Thorax 2003; 58(Suppl II);ii18-ii28
  3. Comparison of Pleural Fluid pH values obtained using blood gas machine, pH meter, and pH indicator strip, Dong-sheng Cheng et al. Chest 1998; 114: 1368-1372.
  4. Biochemical analysis of pleural fluid: what should we measure? Tarn A C & Lapworth R. Ann Clin Biochem 2001; 38: 311-322.
  5. Pleural Effusion., Light R W. NEJM 2002; 346:1971-1977.
  6. Ascitic fluid analysis: the role of biochemistry and haematology., Jeffery J & Murphy M J.  Hospital Medicine 2001; 62: 282-286
  7. The Biochemistry of Body Fluids.  ACBI Scientific Committee Guidelines 2009.



biochemistry, blood sciences, clinical advice

  • Created on .
  • Last updated on .

Copyright heftpathology 2013, 2014, 2015, 2016, 2017, 2018

HTA licence number is 12366

Protection of Personal Information – Laboratory Medicine comply with the Trust Data Protection Policy and have procedures in place to allow the Directorate and it’s employees to comply with the Data Protection Act 1998 and associated best practice and guidance.

The Trust Laboratories at Heartlands Hospital, Good Hope Hospital and Solihull Hospital were awarded UKAS (United Kingdom Accreditation Service) accreditation to the internationally recognised ISO 15189 standard in May 2015. For a list of accredited tests and other information please visit the test database http://www.heftpathology.com/frontpage/test-database.html.
Tests not appearing on this scope are either under consideration or in the process of accreditation and so currently remain outside of our scope of accreditation. However, these tests have been validated to the same high standard as accredited tests and are performed by the same trained and competent staff.

For further information contact Louise Fallon, Quality Manager, 0121 424 1235