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Fluid Analysis Guidelines

Below are some guidelines for fluid analyses which may be of clinical value. Please contact the Duty Biochemist on x16543 if more information is required:

Fluid type

Clinical Indication

Analyses available

Specimen Container

Comments

Ascitic Fluid

? cirrhotic or malignant

Albumin

Total protein

Cholesterol

Triglycerides

LDH

Plain universal

Serum albumin should be simultaneously measured for comparison.

? SBP

 

pH

 

Total protein

See comment

 

Plain universal

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

? pancreatic fistula

?pancreatitis

Amylase

Plain universal

Serum amylase should be measured.

? tubercular

Glucose

Fluoride oxalate (grey top)

 

Chest Drain Fluid

? chylothorax

Chylomicrons

Cholesterol

Triglycerides

Plain universal

 

 

CSF

? bacterial meningitis

Protein

 

Glucose

 

Plain universal

 

 

 

Fluoride oxalate (grey top)

 

? Subarachnoid haemorrhage

Xanthochromia

Plain universal protected from light

Do not use pod system to send sample to lab.

Serum total protein and bilirubin should be measured simultaneously.

?congenital disorder

?cerebral ischaemia

Lactate

Fluoride oxalate (grey top)

Sent to BCH Biochemistry.

?brain metastases

AFP, HCG, placental ALP

Plain Universal

Sent to Charing Cross for analysis.

Diagnosis/investigation of inborn errors of neurotransmitter metabolism

Neurotransmitters

See comment

Specific collection requirements  – contact Duty Biochemist on ext. 16543 well in advance of arranging test.

Sent to Neuroimmunology lab, London.

?narcolepsy with cataplexy

Orexin/Hypocretin

Plain Universal

Sent to Immunology, Oxford.

?neurosarcoidosis

ACE

Plain Universal

CSF total protein also required for interpretation.

Sent to Neurometabolic unit, London.

Cyst Fluid

?thyroid tissue/met

Thyroglobulin

Plain universal

Requires discussion with laboratory prior to request (contact Duty Biochemist on ext. 16543)

Drain Fluid

? contains urine

Urea

Creatinine

Plain universal

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

?biliary fistula

Post surgery

Amylase

Bilirubin

Plain universal

 

Gastric Aspirate

? reflux

?achlorhydria

pH

 

Plain universal

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

Pancreatic Cyst Fluid

 

? Ca pancreas

CEA

CA 19-9

Amylase

Glucose

Plain universal

 

 

Fluoride oxalate (Grey top) required

 

 

 

 

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.

Total Protein

LDH

 

Plain universal

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.

 

Measure serum protein and LDH simultaneously

? infected

pH

 

See comment

This is part of British Thoracic Society’s guidelines for differentiating infective from non-infective pleural effusions, can only be measured on fresh specimen collected anaerobically using a dedicated blood gas analyzer. This analyser can be found on W513 (respiratory).

? chylothorax

Chylomicrons

Cholesterol

Triglyceride

Plain universal

 

? pancreatitis

Amylase

Plain universal

Patient's serum amylase should be measured for comparison.

? rheumatic cause

Glucose

Fluoride oxalate (grey top) tube required.

 

Nasal Fluid

? CSF

Tau protein

Plain universal

Sent to Immunology, Sheffield.

Salivary Cortisol

?Cushing’s

ONDST

Salivary Cortisol

Salivette or Plain universal

Saliva specimens should be collected using a Sarstedt cortisol salivette (these can be requested from Chromatography). Saliva collected into a plain container by passive drool is also acceptable. 

Synovial Fluid

Refer to Microbiology

N/A

 

N/A.

Urine pH

?cause of metabolic acidosis

pH

Plain universal

In patients with a metabolic acidosis and suspected renal tubular acidosis, urine pH measurement is indicated.

 

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