Anaemia — a deficiency of red blood cells or haemoglobin that reduces the oxygen-carrying capacity of the blood — is among the least discussed but most clinically significant consequences of testosterone deficiency in men. Most men with low testosterone and unexplained anaemia have never been told the connection exists. Their fatigue is attributed to the anaemia; their anaemia is attributed to age or unknown causes; and the underlying testosterone deficiency that is driving both goes unaddressed.
At Vitalis Luxe Clinic in Hull, Testosterone and Anaemia is part of our evaluation of men with fatigue and unexplained anaemia — because the testosterone-erythropoiesis relationship is well-established, clinically important, and has direct treatment implications. This article explains the physiology of this relationship, how to recognise anaemia driven by testosterone deficiency, and what happens to red blood cell parameters when TRT is introduced.
Table of Contents
How Testosterone Stimulates Red Blood Cell Production
Testosterone stimulates red blood cell production through multiple mechanisms, collectively referred to as its erythropoietic effects. These mechanisms include:
- Stimulation of erythropoietin (EPO) production — testosterone increases renal EPO synthesis; EPO is the primary hormone driving bone marrow red blood cell production. Higher EPO from adequate testosterone drives higher red cell mass
- Direct bone marrow stimulation — testosterone has direct androgen receptor-mediated effects on erythroid progenitor cells in the bone marrow, promoting their proliferation and differentiation into mature red blood cells independent of EPO
- Iron utilisation — testosterone improves the utilisation of available iron for haemoglobin synthesis, and may reduce hepcidin (the hormone that blocks iron absorption and release), improving iron availability for erythropoiesis
- Stem cell stimulation — androgens promote haematopoietic stem cell activity in the bone marrow, supporting the overall red cell production machinery
The clinical consequence: men with adequate testosterone maintain haemoglobin and haematocrit in the male reference range (haemoglobin 13.5–17.5 g/dL; haematocrit 40–52%). Men with sustained testosterone deficiency lose this erythropoietic drive and may develop a normocytic normochromic anaemia — anaemia with normal red cell size and colour — characteristic of EPO deficiency rather than iron or B12 deficiency.
Testosterone Deficiency and Unexplained Anaemia
| Anaemia Type | Typical Cause | Red Cell Appearance | Testosterone Connection |
|---|---|---|---|
| Iron deficiency anaemia | Insufficient dietary iron or blood loss (GI, menstrual) | Microcytic (small), hypochromic (pale) | Low T reduces iron utilisation efficiency; primarily iron cause but T deficiency compounds |
| B12/folate deficiency | Poor intake, malabsorption | Macrocytic (large) | Not directly testosterone-related |
| Anaemia of chronic disease | Chronic inflammation, autoimmune, renal disease | Normocytic or slightly microcytic | Testosterone deficiency common comorbidity in chronic disease; often compound cause |
| EPO deficiency anaemia | Renal failure, reduced EPO production | Normocytic normochromic | Testosterone directly stimulates EPO; T deficiency reduces EPO drive — classic mechanism |
| Unexplained anaemia of ageing | Common in older men; no identified cause | Normocytic normochromic | Testosterone deficiency is a significant contributor in many cases; TRT Trials found TRT highly effective correction |
| Anaemia in hypogonadal men | Direct consequence of testosterone deficiency | Normocytic normochromic | TRT correction of testosterone restores erythropoietic drive — one of the most reliable TRT outcomes |
The TTrials Anaemia Sub-Study: Definitive Evidence
The most compelling evidence for TRT in testosterone-deficient anaemia comes from the Testosterone Trials (TTrials) Anaemia Sub-Study, published in JAMA Internal Medicine (2017). Among hypogonadal men aged 65+ with unexplained anaemia (haemoglobin 9.5–13.5 g/dL), one year of testosterone gel versus placebo produced the most dramatic results of the entire TTrials programme:
- 72% of men in the TRT group had their anaemia corrected (haemoglobin rose to >13.5 g/dL) versus 14% in the placebo group
- Men with unexplained anaemia showed the largest absolute haemoglobin improvement — mean rise of approximately 1.0 g/dL
- Men with known anaemia cause also improved, but less dramatically than those with unexplained anaemia
- The response was rapid — meaningful haemoglobin improvements visible within 3 months of TRT initiation
These findings are clinically striking. For older hypogonadal men with unexplained anaemia, TRT is among the most effective available interventions — producing correction rates that no other single non-transfusion treatment reliably achieves in this population. The connection between unexplained anaemia in older men and testosterone deficiency is underappreciated in standard clinical practice, where testosterone assessment is not routinely performed as part of anaemia workup.
The Other Side: Erythrocytosis as a TRT Risk
The same erythropoietic potency of testosterone that makes TRT effective for anaemia creates the erythrocytosis risk that is the most clinically important safety monitoring parameter on TRT. In men without anaemia who start TRT, haematocrit may rise above the normal range (>52% in men) — a condition called erythrocytosis or polycythaemia. Elevated haematocrit increases blood viscosity, which raises the risk of thromboembolic events including deep vein thrombosis and pulmonary embolism.
- Erythrocytosis is more common with injectable TRT (particularly at higher doses) and scrotal cream preparations; gels carry lower erythrocytosis risk
- Older men, smokers, men with sleep apnoea, and men with baseline high-normal haematocrit are at higher risk
- Monitoring at 6–8 weeks after initiation, at 3 months, then 6-monthly is the standard protocol at Vitalis Luxe Clinic
- Management options include dose reduction, preparation switch, increased hydration, or therapeutic venesection (phlebotomy) if haematocrit is significantly elevated
- Target haematocrit on TRT: below 52% — doses are adjusted to keep within this range
| The Clinical Paradox Testosterone’s erythropoietic effect is both its most powerful therapeutic action for anaemic hypogonadal men and its most important safety risk for non-anaemic men. The same mechanism — EPO stimulation and direct bone marrow erythropoiesis — that corrects anaemia in deficient men raises haematocrit in replete men. This is why baseline haematocrit before TRT and regular monitoring thereafter are non-negotiable, and why dose calibration to achieve testosterone benefit without erythrocytosis is a core clinical skill in TRT management. |
Frequently Asked Questions
Can low testosterone cause anaemia?
Yes — testosterone deficiency is an underrecognised cause of normocytic normochromic anaemia, particularly in older men. Testosterone drives red blood cell production through EPO stimulation, direct bone marrow effects, and iron utilisation support. When testosterone falls significantly, erythropoietic drive reduces and haemoglobin may fall. The TTrials Anaemia Sub-Study found that 72% of hypogonadal men with unexplained anaemia had their anaemia corrected by one year of TRT versus 14% on placebo — one of the most striking findings in TRT clinical trial history.
Will TRT increase my haemoglobin?
In men who are anaemic or borderline-anaemic at baseline, TRT reliably increases haemoglobin — with meaningful rises visible within 3 months. In non-anaemic men, haemoglobin and haematocrit typically rise modestly within the normal range. In a minority of men — particularly those using injectable TRT or scrotal cream, older men, smokers, and men with sleep apnoea — haematocrit may rise above normal (erythrocytosis), requiring dose reduction or management.
What is erythrocytosis and how is it managed on TRT?
Erythrocytosis on TRT is an elevated haematocrit (above 52% in men) caused by TRT’s erythropoietic stimulation. It increases blood viscosity and thromboembolic risk. Management depends on severity: mild elevation prompts dose reduction or preparation switch; significant elevation may require therapeutic venesection (phlebotomy — blood removal equivalent to a blood donation). At Vitalis Luxe Clinic, haematocrit is monitored at 6–8 weeks, 3 months, and 6-monthly, and doses are adjusted to keep haematocrit below 52%.
Should testosterone be tested as part of anaemia workup in men?
Yes — particularly in older men with normocytic normochromic unexplained anaemia. Testosterone deficiency is a significant and underappreciated contributor to anaemia in older men, and it is not routinely included in standard NHS anaemia workup. At Vitalis Luxe Clinic, we assess testosterone as part of our evaluation of men presenting with significant fatigue and anaemia, recognising that the two are frequently co-occurring and causally related.
Is anaemia from low testosterone dangerous?
Anaemia from any cause can be clinically significant — reducing oxygen delivery to tissues, causing fatigue, exertional breathlessness, reduced cognitive function, and in older men contributing to falls and cardiac stress. Testosterone-deficiency anaemia is correctable with TRT — making it one of the most actionable causes of unexplained anaemia in hypogonadal men. Leaving it untreated prolongs an avoidable physiological deficit.
Does giving blood affect TRT?
Men on TRT with elevated haematocrit who undergo therapeutic venesection are effectively donating blood volume, which acutely reduces haematocrit. UK Blood services do not currently accept blood donations from men on TRT — venesection for erythrocytosis management is therefore performed as a clinical procedure rather than through blood donation. Patients should discuss haematocrit management with their prescribing clinician rather than self-managing through unofficial donation channels.
Where can I get my testosterone tested for anaemia in Hull or Yorkshire?
Vitalis Luxe Clinic in Hull assesses testosterone alongside haematological parameters as part of comprehensive men’s health evaluation. If you have unexplained fatigue, low haemoglobin, or have been told you have anaemia without a clear cause, testosterone assessment should be part of your workup. We serve men across Hull, East Yorkshire, and throughout Yorkshire..