Blood count

When and why

A blood count is a routine haematology test. It can be done as part of a general investigation of an acute illness, for regular monitoring of HIV infection, and to check for drug side-effects. To do this test, a small sample of blood is taken from a vein in the arm (venesection or venepuncture).

How it will help

A full blood count (FBC), also known as a complete blood count (CBC) can:

  • Detect whether someone is anaemic. Anaemia is a shortage of haemoglobin, the substance that allows red blood cells to transport oxygen to the body's tissues. Normal haemoglobin levels in HIV-negative people are 12 to 16 grams per decilitre for women and 13.5 to 18 for men, but are often a little lower in people with HIV. Anaemia can contribute to the symptoms of fatigue and breathlessness. It is more common among people with HIV than in the general population and may be caused by HIV itself, opportunistic infections or certain antiretroviral drugs (e.g. zidovudine/AZT).
  • Measure the haematocrit, which is the percentage of red blood cells in the total blood volume. It shows the oxygen-carrying capacity of the blood and tells whether the blood is too thick or too thin. The average range is 40 to 54 percent.
  • Measure the number and different types of white cells in the blood. The total number of white blood cells in an average healthy adult is 4000 to 11,000. If there are insufficient numbers of white cells, especially of neutrophils (neutropenia), then the risk of bacterial and fungal infections is higher. However, this only applies to neutrophil levels below 500. People with HIV often have slightly lower levels of neutrophils than normal and this is not significant. Neutropenia can be a side-effect of treatment of AZT, ganciclovir or cancer chemotherapy. It can be treated by reducing or stopping the dose of these drugs, or with G-CSF, which increases the number of neutrophils in the blood by stimulating production in the bone marrow. Eosinophils are white cells involved in allergic-type reactions. Their number can be elevated during certain parasitic infections. A normal amount is 0 to 8% of the total white blood cell count. The lymphocyte count is also measured and used to calculate the CD4 lymphocyte count, another important special blood count in monitoring HIV infection (see below).
  • Measure the level of platelets. These are small cells essential for normal blood clotting. A shortage of platelets (thrombocytopenia) may result in easy bruising and bleeding. An excess of platelets can make the blood flow too stodgy. An average count is 150 to 440, although people with HIV often have fewer than average. As long as the count is not too low, the condition does not need treatment. If it gets so low that bleeding occurs, treatment with intravenous gammaglobulin or steroids may be required.
Community Consensus Statement on Access to HIV Treatment and its Use for Prevention

Together, we can make it happen

We can end HIV soon if people have equal access to HIV drugs as treatment and as PrEP, and have free choice over whether to take them.

Launched today, the Community Consensus Statement is a basic set of principles aimed at making sure that happens.

The Community Consensus Statement is a joint initiative of AVAC, EATG, MSMGF, GNP+, HIV i-Base, the International HIV/AIDS Alliance, ITPC and NAM/aidsmap

This content was checked for accuracy at the time it was written. It may have been superseded by more recent developments. NAM recommends checking whether this is the most current information when making decisions that may affect your health.

NAM’s information is intended to support, rather than replace, consultation with a healthcare professional. Talk to your doctor or another member of your healthcare team for advice tailored to your situation.