If you’ve ever wondered about PCV vs haematocrit, you’re certainly not the only one.

You might hear someone say, “The PCV is 38%.”

Someone else might say, “The HCT is 38%.”

And then you’re left wondering whether they’re actually talking about the same thing.

In many clinical situations, PCV and haematocrit are used almost interchangeably. But there are some important differences in how the measurements are obtained.

If you’re a vet nurse and wanting to delve more into PCV’s, take a read of 7 Essential Facts About Manual PCV Every Veterinary Nurse Should Know

What is PCV?

PCV stands for packed cell volume.

It is traditionally measured using a manual technique.

A small blood sample is placed into a capillary tube and centrifuged.

The red blood cells pack towards the bottom of the tube, and the percentage of the blood column occupied by those packed cells is measured.

For example, a packed cell column occupying 40% of the tube gives a PCV of 40%.

What is haematocrit?

Haematocrit, usually abbreviated to HCT, also describes the proportion of blood occupied by red blood cells.

However, HCT is commonly reported by automated haematology analysers.

The analyser calculates the value using measurements of the red blood cells and their characteristics.

So, when discussing PCV vs haematocrit, the biggest practical difference is often how the result was obtained.

Are PCV and HCT measuring the same thing?

Broadly speaking, yes.

Both are measurements relating to the proportion of blood made up of red blood cells.

That’s why the two terms are frequently used as though they’re interchangeable.

But the actual measurement methods aren’t identical.

A manual PCV is physically measuring the packed red cell column after centrifugation.

An automated HCT is calculated by the analyser from its red cell measurements.

Why might PCV and HCT be slightly different?

You might occasionally see a manual PCV and analyser HCT that aren’t exactly the same.

That’s not necessarily a problem.

Different methodologies can produce slightly different results.

The manual PCV can also be influenced by factors such as:

• Sample quality
• Centrifugation
• Tube filling
• Reading technique
• Plasma trapped between packed red cells
• Inclusion or exclusion of the buffy coat

Automated analysers have their own measurement principles and potential limitations.

Does that mean one is better?

Not necessarily.

It depends on what you’re trying to achieve.

An automated analyser provides a much broader range of haematological information, including things such as:

• RBC count
• Haemoglobin
• HCT
• MCV
• MCH
• MCHC
• Reticulocytes, depending on the analyser

A manual PCV is much simpler.

But that’s part of its appeal.

If you need a quick estimate of red cell volume in a patient, a manual PCV can be incredibly useful.

Why do veterinary nurses still use manual PCVs?

Because they’re quick.

They’re also relatively inexpensive and require minimal equipment.

In emergency or inpatient situations, being able to produce a PCV and total solids result quickly can be useful when assessing a patient.

They can also be helpful when an analyser result doesn’t seem to fit the clinical picture.

What about haemoglobin?

Haemoglobin and PCV/HCT are related, but they’re not the same measurement.

Haemoglobin measures the amount of haemoglobin in the blood.

PCV/HCT measures the proportion of blood occupied by red blood cells.

They’re therefore different ways of assessing aspects of red cell status.

What if the PCV and HCT don’t match?

First, don’t panic.

Consider the size of the difference.

Small differences may be expected because of methodology.

If the discrepancy is significant or unexpected, investigate further.

Check:

• Sample quality
• Whether the samples were collected at the same time
• Whether the patient received fluids between tests
• Whether one result was manual and the other automated
• Whether there could have been an analyser or technique issue

The clinical picture should always be considered.

Why is this important for veterinary nurses?

Understanding PCV vs haematocrit helps you communicate blood results accurately.

If you’re handing over a patient and say the PCV is 24%, it’s useful to know whether that came from a manual PCV or an analyser’s HCT.

Likewise, when comparing results over time, try to make sure you’re comparing like with like where possible.

A patient’s HCT from an analyser isn’t necessarily directly interchangeable with a manually obtained PCV for every clinical purpose.

PCV and HCT in anaemia

Both can be useful when monitoring anaemia.

For example, if a dog’s PCV was 35% yesterday and is now 28%, that’s a meaningful change.

Similarly, a falling HCT on an analyser can show that the patient’s red cell proportion is decreasing.

Again, trends are often more useful than one isolated number.

Final thoughts

When it comes to PCV vs haematocrit, the simplest way to remember it is:

PCV = traditionally a manually measured packed cell volume.

HCT = commonly an analyser-derived haematocrit.

They describe very similar biological information, but the methods used to obtain them can differ.

For day-to-day veterinary nursing, the important thing is understanding what your result represents and being aware of how it was measured.