When interpreting the often misinterpreted and underused PCV and total solids test, it is important to take note of the serum colour as this may give clues into the diagnosis.

PCV tubes
Normal serum colour (left) compared to a patient with immune-mediated haemolytic anaemia. The serum is haemolysed and anaemia is present.

The most common abnormalities seen in clinic are icteric, haemolysed and lipaemic serum.

Clear serum can also be of importance – especially when you interpret it with blood counts and urine colour.

Haemolysis

The most common abnormality of serum colour changes is haemolysis. In my experience, the most common cause is suboptimal collection technique. To confirm this, simply collect another sample and repeat.

If it is repeatable, and concurrent anaemia or pigmenturia is present, it warrants further investigation.

Intravascular haemolysis can be caused by:

  • immune-mediated haemolytic anaemia
  • blood transfusion reactions
  • infectious diseases such as Mycoplasma haemofelis, Babesia canis, Ehrlichia canis, FeLV and others
  • Heinz bodies from the ingestion of heavy metal, onions or paracetamol
  • hypophosphataemia
  • macroangiopathic disease (neoplasia, for example)
  • envenomation – typically, snake bites

Testing issues

Haemolysis can also affect other laboratory testing. It can lead to an artefactual increase in glucose, phosphorus, bilirubin, total protein, fructosamine and triglycerides, and a decrease in sodium (pseudohyponatraemia), cholesterol, calcium, potassium and albumin.

Extravascular haemolysis often does not cause haemolysed serum as it is generally slower and the body is able to clear the haemoglobin before it can lead to discolouration of the serum.

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