Body Fluids Flashcards
Why fluids need their own validation process
Different matrix could cause interference and inaccuracy
Important considerations for workflow for body fluid specimens
Route, equipment, mechanism determined by clinician
Tube types, containers, volume, temperature, timeliness of transport to be clearly communicated by lab. Speci will likely be needed by multiple departments.
Method validation of body fluids
Guideline - CLSI Analysis of Body Fluids in Clinial Chemistry - a risk based approach to desiging body fluid validation studies.
Purpose is to ensure matrix effects do not interfere with the accurate measurement of analytes.
Validation requirements determined by local and federal laws ie TGA regulations, NPAAC and NATA requirements
Possible requirements include: trueness, precision, analytical sensitivity, analytical specificity/interfering substances, reportable range, reference intervals, treatment if fluid is viscous
At WDP, Fluid Validation Plan:
Determine which sample types to validate - pleural, ascitic, drain
Determine which analytes to validate - albumin, amylase, total bilirubin, cholesterol, creatinine, glucose, LDH, lipase, total protein, Tg, Na, K, Urea, NT-ProBNP
Protocol: Precision, stability, linearity, matrix (recovery after addition of serum), reference intervals
IT modification of panels as required.
Important matrix differences in body fluids
Protein (usually low)
Different pH
Different ionic strength
Altered viscosity
LP tube order and distribution to departments?
Tube 1 - biochem
Tube 2 - micro (Gram stain)
Tube 3 - cyto (cell count and differential)
Tube 4 - CSF xanthochromia (protect from light)
Indications for LP
CNS infection
SAH
Malignancy
Demyelinating disease
Inflammatory CNS disease suspected
Most common causes of pleural effusion
Congestive heart failure
Malignancy
Pneumonia
Indication for diagnostic peritoneal lavage and investigations performed
To predict the need for surgical intervention on patients after blunt abdominal trauma.
Positive if aspiration of blood.
Otherwise, instil 1L saline, mix and drain by gravity.
Perform cell count and pancreatic enzymes
Sample type considerations
Pleural - EDTA to reduce WBC clumping, heparin on ice for pH measurement
Peritoneal - direct inoculation into culture bottles
Synovial fluid - EDTA to reduce WBC clumping and to allow assessment of fibrinogen
CSF C-amyloid (A-beta protein) adsorbs to polystyrene not polypropylene tubes.
The only common analytes known to have limited stability in body fluids
pH
Glucose in cellular specis
Lactate dehydrogenase when stored refrigerated/frozen
Ways to assess fluid viscosity
String test
Drop test
How does viscosity interfere with testing
Pipette unable to withdraw accurate volume
Biochemistry of chylothorax
A pleural fluid triglyceride concentration >1.24 mmol/L strongly supports the diagnosis of chylothorax. A triglyceride <0.56 mmol/L with a cholesterol >5.18 mmol/L is found in
pseudochylothorax.
Light’s criteria (1 of 3 required)
- pleural fluid-to-serum protein ratio >0.5
- pleural fluid-to-serum LDH >0.6
- pleural fluid LDH activity
that is >2/3 the upper limit of normal serum LDH activity
Alternatives to Light’s criteria if serum unavailable
pleural fluid protein concentration >30 g/L or a pleural fluid cholesterol >1.2 mmol/L has been found to indicate the presence of an exudative effusion as accurately as Light’s
criteria
