Using the results of the PCV and TS is a quick and simple way to provide you with additional information regarding your patient. However, they must be used in conjunction with clinical and other data, and not interpreted on their own. For example, if both the PCV and TS are normal, you cannot rule out dehydration; patient's clinical signs, such as skin tent time and mucous membranes, must also be assessed.
In addition, never forget your blood smear when interpreting results! It can provide valuable additional information when you suspect certain conditions, especially the different types of anaemia.
The table below gives a summary of the conditions that may result in specific changes to the PCV and TS.
| PCV | TS | Interpretation |
|---|---|---|
| Increased | Increased | Dehydration; water loss causes both values to increase. Always check clinical signs. |
| Increased | Normal | An increase in RBC e.g. splenic contraction. Dehydration with concurrent hyperproteinaemia. Other causes are uncommon to rare e.g. polycythaemia vera. |
| Increased | Decreased | Severe dehydration with protein loss; haemorrhage with splenic contraction; acute haemorrhagic diarrhoea syndrome. |
| Normal | Increased | Anaemia with dehydration, normal hydration with hyperproteinaemia or hyperglobulinaemia, lipaemia. |
| Normal | Normal | Normal hydration. Acute haemorrhage is also possible, before fluid moves between compartments to compensate. |
| Decreased | Increased | Lymphoproliferative disease, anaemia of chronic disease. |
| Decreased | Normal | Anaemia (RBC destruction/loss, decreased RBC production). |
| Decreased | Decreased | Aggressive fluid therapy, blood dilution (usually greater than 3 hours post-haemorrhage). |
There are some common pitfalls which you should avoid when assessing the above.
Does an increase in PCV always mean dehydration?
No. Dehydration is a common cause for an increase in PCV. However, this can also occur during times of stress when the spleen contracts (a natural occurrence to increase oxygen-carrying capacity). This will raise the number of RBC and increase PCV.
Acute haemorrhagic diarrhoea syndrome (formerly haemorrhage gastroenteritis) can also cause PCV to increase. TS can be normal or raised.
Shouldn't PCV decrease with acute haemorrhagic diarrhoea syndrome?
With this syndrome, it is often assumed that the frank blood loss that occurs would result in a decreased PCV. This is not the case, and typically PCV is increased due to reasons such as concurrent marked dehydration.
Does a normal PCV rule out blood loss?
No. In the acute stages of blood loss, PCV and TS can be normal. This will occur before the patient has replaced water through drinking or via IV fluid therapy, or extravascular fluid has shifted compartments to replace the loss. In the subacute stages, PCV and TS will start to decrease as haemodilution occurs to compensate the loss.