What Does Low Haemoglobin Mean? Anaemia Explained

Haemoglobin is a protein in red blood cells that carries oxygen throughout your body. A low level means your blood carries less oxygen than expected for your age and sex [WHO, 2011].

What does haemoglobin do in the body?

Haemoglobin is an iron-rich protein found inside red blood cells [WHO, 2011]. It binds to oxygen in the lungs and delivers it to body tissues [WHO, 2011].

A complete blood count test measures the concentration of this protein in whole blood [CLSI, H20-A2]. Normal levels ensure your tissues receive adequate oxygen for energy production [WHO, 2011].

How is low haemoglobin defined by the WHO?

The World Health Organization defines anaemia using specific haemoglobin thresholds based on age and sex [WHO, 2011]. For non-pregnant women, anaemia is defined as haemoglobin below 12.0 g/dL [WHO, 2011]. For men, the threshold is below 13.0 g/dL [WHO, 2011].

For pregnant women and young children, the threshold is typically below 11.0 g/dL [WHO, 2011]. Values below these limits indicate reduced oxygen-carrying capacity in the bloodstream [WHO, 2011].

Which lab tests provide context for low haemoglobin?

A red blood cell count measures the total number of circulating red cells [CLSI, H20-A2]. Serum ferritin tests measure stored iron levels in the body [WHO, 2020].

Serum iron measures the iron currently circulating in liquid blood [NICE, 2021]. Together, these tests help identify whether iron availability relates to the lower reading [WHO, 2020].

What everyday factors can temporarily lower haemoglobin?

Plasma volume expansion during normal pregnancy naturally lowers measured haemoglobin concentration [WHO, 2011]. High fluid intake or intravenous fluids can also temporarily dilute blood samples [CLSI, H20-A2].

Frequent blood donation can lower iron stores and reduce haemoglobin numbers over time [WHO, 2020]. Recent heavy menstrual bleeding can also cause a temporary dip in measured levels [NICE, 2021].

Frequently asked questions

What is a normal haemoglobin range for adult men?

For adult men, normal haemoglobin is generally 13.0 g/dL or higher [WHO, 2011]. Reference ranges can vary slightly by laboratory [CLSI, C28-A3].

What is a normal haemoglobin range for adult women?

For non-pregnant adult women, normal haemoglobin is generally 12.0 g/dL or higher [WHO, 2011]. Laboratory reference ranges can vary depending on the testing method [CLSI, C28-A3].

Does a low haemoglobin result always mean an iron deficiency?

No, low haemoglobin does not always point to low iron [WHO, 2020]. Other nutritional factors or inherited red blood cell traits can also lower values [WHO, 2011].

How does ferritin relate to haemoglobin?

Ferritin measures stored body iron, which is necessary to build haemoglobin molecules [WHO, 2020]. Low ferritin often appears before haemoglobin levels begin to drop [WHO, 2020].

Can hydration levels affect a haemoglobin test result?

Yes, drinking large volumes of water can dilute the blood sample [CLSI, H20-A2]. This dilution can cause a temporarily lower reading [CLSI, H20-A2].

Sources

• World Health Organization (WHO). Haemoglobin concentrations for assessing anaemia and clinical management, 2011.
• Clinical and Laboratory Standards Institute (CLSI). Reference Intervals and Clinical Decision Limits, Guideline C28-A3, 2010.
• Clinical and Laboratory Standards Institute (CLSI). Reference Leukocyte and Platelet Counts, H20-A2, 2007.
• World Health Organization (WHO). WHO guidance on serum ferritin concentrations, 2020.
• National Institute for Health and Care Excellence (NICE). Anaemia: assessment and clinical management, 2021.