Blood count and blood group
Reticulocyten
The number of young red blood cells; shows whether the bone marrow is making enough new red blood cells, especially in anemia.
Everything about this testWhat it measures
Reticulocytes are young, not yet fully mature red blood cells that the bone marrow has just released. A red blood cell lives about 120 days, so the bone marrow has to make new ones every day. The number of reticulocytes shows how hard the bone marrow is making red blood cells at this moment. The result is given as a percentage of the red blood cells or as a number per liter of blood.
- Anemia due to blood loss or due to faster breakdown of red blood cells (hemolysis), with a raised number
- Anemia because the bone marrow makes too few cells, for example due to a deficiency of iron, vitamin B12 or folic acid, with a low number
- Recovery of production after starting iron, vitamin B12 or folic acid
High
A raised number of reticulocytes means that the bone marrow is making extra red blood cells. Together with anemia, this fits blood loss, for example after bleeding or heavy menstruation, or faster breakdown of red blood cells (hemolysis), due to an inherited abnormality, an immune reaction or some medicines. A rise without anemia also occurs in the weeks after starting iron, vitamin B12 or folic acid, after donating blood and when staying at high altitude. Symptoms do not come from the number itself, but from the cause; with breakdown of red blood cells these can be tiredness, yellowing of the skin or eyes and dark urine.
Low
A low number of reticulocytes means that the bone marrow is making few new red blood cells. Together with anemia, this usually fits a deficiency of iron, vitamin B12 or folic acid, a chronic illness or kidney disease (too little of the hormone EPO) or a viral infection that temporarily slows production. Radiotherapy, chemotherapy and some other medicines also lower production. Rarely: a bone marrow disorder, almost always together with other abnormalities in the blood count. Without anemia, a slightly low number usually has no meaning.
If your result is abnormal
With anemia and a raised number of reticulocytes, the GP looks for blood loss and checks the LDH; if faster breakdown of red blood cells is suspected, the GP refers to an internist-hematologist according to the NHG guideline. With anemia and a low number, the GP looks at ferritin, vitamin B12, folic acid and kidney function, and consults an internist-hematologist if the white blood cells or platelets are abnormal or the cause is unexplained.
Reliability
Counting reticulocytes is accurate, but the result can only be interpreted together with the hemoglobin and the MCV. The test is mainly used in anemia to distinguish whether the bone marrow makes too little or whether too much is being lost, and to follow the effect of treatment. The Dutch GP guideline (NHG) on anemia has reticulocytes measured when anemia due to a deficiency of vitamin B12 or folic acid is suspected, and sees a raised number together with a raised LDH as a sign of faster breakdown of red blood cells. In people without anemia, a slightly abnormal number means little.
Limitations
- In anemia, the percentage of reticulocytes comes out higher than the actual number, because there are fewer red blood cells; the number per liter is then easier to interpret.
- Bleeding, donating blood or starting iron, vitamin B12 or folic acid in the weeks before the sample collection raises the number.
- Staying at high altitude or using EPO raises the number; a recent viral infection can temporarily lower it.
- Reference values differ by laboratory; the result is given as a percentage or as a number per liter.
How common is this
Anemia is newly diagnosed in general practice in about 9 in 1000 people per year, usually due to iron deficiency, with a normal or low number of reticulocytes. Anemia due to faster breakdown of red blood cells, with a high number, is much rarer.
Who is this useful for
Useful with anemia whose cause is unclear, when faster breakdown of red blood cells is suspected, and to see whether production recovers after treatment with iron, vitamin B12 or folic acid. For healthy people without anemia or symptoms, the test adds little.
Downsides and risks
- A slightly abnormal number without anemia, for example after donating blood or in athletes, can cause unnecessary worry or unnecessary further tests.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results