Reticulocyte percentage

Some laboratories use 0.2 to 2.0; the percentage is influenced by the red cell count, so the absolute count is often preferred; use the range your lab printed.

This is the reticulocyte count expressed as a percentage of all the red blood cells, rather than as an absolute number. The two are usually printed together. Because it is a percentage, it reads higher when the total number of red cells is low even if the marrow is making them at a normal rate.

It is printed alongside the absolute reticulocyte count and answers the same question: is the bone marrow making new red cells at the expected rate? Many haematologists prefer the absolute count for this reason, but the percentage is still widely printed.

• Recent blood loss
• Conditions where red cells are broken down early (haemolysis)
• The first weeks of iron, vitamin B12 or folate replacement
• Recovery of the bone marrow after chemotherapy
• Anaemia of any cause, simply because the percentage is of a smaller total

• Low iron, vitamin B12 or folate
• Long-term kidney disease
• Bone marrow conditions
• Chemotherapy and radiotherapy
• Long-term inflammatory illness

• A rise after blood donation or in the first fortnight of iron or vitamin replacement is expected
• Because it is a percentage, it reads a little higher whenever the red cell count is low
• Analysers measure it with limited precision

No fasting needed. Best read together with the absolute count and the haemoglobin.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.