How do I avoid haemolysis getting in the way of important results?
By Joanne Lewis BSc BVMS (Hons) MRCVS
Artefactual haemolysis can really be a nuisance when it comes to interpreting results. There is nothing worse than painstakingly drawing a sample from a pet belonging to the most obnoxious client on your books, only to receive a clinical pathologist's comment suggesting that it will be difficult to interpret the significance of the tests you requested because the sample was grossly haemolysed!
Common Cause of Clotting in an EDTA Sample
Samples should be mixed gently, but thoroughly, IMMEDIATELY after taking the blood for EDTA tubes.
This will prevent blood clotting, therefore unnecessary re-bleeding of the patient.
A blood smear should also be sent at the same time, this would enable us to give at least some haematology results even if the sample is clotted.
Measuring Glucose Levels in Blood
Only use fluoride oxalate tubes to measure glucose levels in blood!
Glucose values in unpreserved blood samples decrease quickly after collection as glucose is metabolised by the red blood cells.
The additives contained in fluoride/Oxalate tubes will stop enzymatic activity at the glycolytic pathway, therefore preserving the glucose levels for a longer period of time and giving a more accurate result.
Never Mix Blood from one Perservative to another
Never mix blood from one preservative to another, for instance, if an EDTA blood sample is mixed with a Heparin or Gel tube this would contaminate the Biochemistry tests. In particular, EDTA reduces calcium ions and increases the k+ ion levels, and also affects numerous other enzymes.
Use of Serum for Glucose Monitoring
Please remember that it is possible to obtain accurate glucose results from serum samples which have been spun and separated quickly after sampling. The recommendation is to spin and separate the serum 30 - 60 minutes after collection.
Particularly in those animals where the volume of blood collected is limited, this avoids the need to use 1 ml of blood to obtain one biochemical parameter.
From our experience, due to problems with mixing of fluoride oxalate, we often obtain more accurate glucose results from the serum sample when checking those “low” glucose results obtained from the fluoride oxalate sample submitted.