Fluid Analysis Guidelines

Written by Craig Webster on 28 February 2014.

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	Comments

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	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	Amylase	Patient's serum amylase should be measured for comparison.
	? rheumatic cause	Glucose	Fluoride oxalate tube required.

Ascitic Fluid	? cirrhotic or malignant	Albumin, LDH, Cholesterol	Serum albumin should be simultaneously measured for comparison
	? SBP	pH, Protein	For rare instances pH should be collected anaerobically with heparin and then measured in a blood gas analyser using clot filter.
	? tubercular	Glucose	Fluoride oxalate tube required.
	? pancreatic fistula	Amylase	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
Drain Fluid	Post surgery	Amylase, bilirubin

CSF	? bacterial meningitis	Protein, glucose, lactate	Glucose & lactate needs fluoride oxalate tube
CSF	? 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	pH	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	? CSF	Tau protein	Dispatch to specialist referral centre.

Pancreatic Cyst Fluid	? Ca pancreas	CEA, CA 19-9

References:

BTS guidelines for the investigation of a unilateral pleural effusion in adults, Maskell N A et al. Thorax 2003; 58(Suppl II):ii8-ii17
BTS guidelines for the management of pleural infection, Davies C W H et al. Thorax 2003; 58(Suppl II);ii18-ii28
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.
Biochemical analysis of pleural fluid: what should we measure? Tarn A C & Lapworth R. Ann Clin Biochem 2001; 38: 311-322.
Pleural Effusion., Light R W. NEJM 2002; 346:1971-1977.
Ascitic fluid analysis: the role of biochemistry and haematology., Jeffery J & Murphy M J. Hospital Medicine 2001; 62: 282-286
The Biochemistry of Body Fluids. ACBI Scientific Committee Guidelines 2009.

biochemistry, blood sciences, clinical advice

Created on 28 February 2014.
Last updated on 15 August 2018.