Low Haematocrit: What It Means

Blood is part cells and part liquid. Haematocrit is the percentage of the total volume that is occupied by red blood cells. Lab Tests Online UK describes the PCV test as measuring the proportion of blood made up of red blood cells and says it helps assess conditions such as anaemia, dehydration or polycythaemia.

It is requested as part of a full blood count, often because of symptoms such as headaches, blurred vision, tiredness, itchy skin, difficulty breathing and dizziness. It is also repeated at regular intervals to monitor anaemia, polycythaemia or dehydration, to look at the need for or effect of blood transfusion, and to check the severity of ongoing bleeding.

Because it is a proportion rather than a count, haematocrit reacts to both the number of red cells and the amount of fluid they are suspended in. That is why it can fall for two quite different reasons.

Lab Tests Online UK states that a decreased PCV indicates anaemia or haemodilution. For anaemia it lists conditions that can result in a low PCV, which it groups as follows.

Lab Tests Online UK says haemodilution is usually obvious because it follows a bolus of intravenous fluids, or because of pregnancy. In pregnancy the volume of fluid in the blood increases, so the red cells are spread through more plasma and the haematocrit falls slightly without any loss of cells.

It also states that women of childbearing age may have temporary decreases in PCV during menstrual periods and pregnancy, and that a recent blood transfusion may give a misleading result. These are reasons for a clinician to ask about context before interpreting a single low number.

A result that is low only marginally, in someone who feels well and whose haemoglobin and cell size look otherwise typical, is therefore more likely to be repeated than pursued.

Lab Tests Online UK says further testing may be necessary to determine the exact cause of anaemia. It lists iron tests, vitamin B12 and folate, a reticulocyte count, a blood film and, in some cases, bone marrow examination among the tests that may be used to evaluate anaemia.

If anaemia is iron deficiency, the NHS says the GP may ask about lifestyle and medical history, arrange a full blood count and, when the reason is unclear, a faecal immunochemical test and specialist referral. NICE Clinical Knowledge Summaries says the underlying cause of iron deficiency anaemia should be determined and treated.

• Look at haemoglobin and the red cell count on the same report. A low haematocrit with normal values for both is a different story from all three being low.

• Think about blood loss, pregnancy, recent intravenous fluids or a recent transfusion.

• Tell your doctor about all medicines, because some can lower red cell numbers.

• Ask which follow-up blood tests are planned and when the count will be rechecked.

Lab Tests Online UK says treatment depends upon the type of anaemia and the cause, and that folic acid, vitamin B12 replacement, iron and packed red cell transfusion are some of the therapies used. The NHS states that, once the reason for iron deficiency anaemia has been found, the GP will recommend treatment, and iron tablets are usually taken for about 6 months.

Where the cause is a kidney, liver, inflammatory or marrow condition, treatment is directed at that condition and the haematocrit usually follows. Lab Tests Online UK adds that diet and nutrition help prevent deficiency anaemias but are not likely to correct a problem caused by disease.