Haematocrit

Haematocrit measures the percentage of your total blood volume that is made up of red blood cells, giving a useful indication of how concentrated or dilute your blood is. While related to your red blood cell count and haemoglobin, haematocrit adds another dimension by showing the balance between the cellular and liquid components of your blood. This balance matters more than you might think. Blood that has a healthy proportion of red blood cells flows smoothly through your vessels, delivering oxygen efficiently without placing unnecessary strain on your heart. If the proportion is too low, it may suggest your oxygen-carrying capacity is reduced; if it is too high, your blood becomes thicker and your cardiovascular system has to work harder to pump it around. Either way, knowing your haematocrit helps build a fuller picture of your overall blood health.

Imagine your blood as a well mixed smoothie, the red blood cells are the fruit and the plasma is the liquid base. Haematocrit essentially tells you what fraction of the glass is fruit versus liquid. Your body carefully regulates this ratio through a combination of red blood cell production in the bone marrow, the natural breakdown of ageing cells, and fluid balance managed by your kidneys. When everything is working harmoniously, the proportion stays remarkably stable.

Dehydration is one of the most common reasons for a temporarily elevated haematocrit, when you lose fluid through sweating, illness, or simply not drinking enough, the plasma volume drops and the red cell percentage rises even though the actual number of cells has not changed. Conversely, overhydration or significant fluid retention can lower it. Iron status, altitude, and fitness level also play a role. If your haematocrit sits outside the normal range, a conversation with your GP is a sensible next step to understand what might be driving it and whether any action is needed.