Evidence question

PubMed sourcedAbstract-based analysisUpdated Sep 2026Human reviewedUpdated Aug 2026

Evidence / Men's Hormone Health

CoverageMen's Hormone Health

Does testosterone therapy increase hematocrit and polycythemia risk?

Reviewed by Neal Rouzier, MD, Preventive Medicine · Aug 2026

Updated Aug 2026·14 studies analyzed·2 core studies·Applies to: hypogonadal men

Bottom line

Testosterone therapy commonly raises hematocrit; polycythemia is a recognized adverse effect requiring dose adjustment, formulation changes, or phlebotomy when thresholds are exceeded.[1–6]

Evidence confidence

Evidence Confidence

High
LimitedModerateHigh

Multiple high-quality studies directly address this question, with generally consistent findings.

Key uncertainty. Optimal hematocrit monitoring thresholds and phlebotomy triggers vary by guideline, formulation, and patient comorbidity.

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Also asked

Can testosterone cause high hematocrit levels?▼

Yes — testosterone therapy commonly raises hematocrit through increased erythropoiesis. Monitor hematocrit at baseline and during follow-up.

Can too much testosterone cause polycythemia?▼

Exogenous testosterone is a recognized cause of secondary polycythemia. Dose reduction, formulation change, or therapeutic phlebotomy may be required when thresholds are exceeded.

How to lower hematocrit on TRT?▼

First reduce dose or switch formulation if hematocrit exceeds guideline thresholds. Therapeutic phlebotomy is used when elevation persists; evaluate for other causes of erythrocytosis.

TRT erythrocytosis▼

TRT erythrocytosis reflects testosterone-stimulated red cell production. It is expected in a subset of patients and requires active monitoring rather than passive observation.

Testosterone hematocrit monitoring▼

Testosterone therapy commonly raises hematocrit; polycythemia is a recognized adverse effect requiring dose adjustment, formulation changes, or phlebotomy when thresholds are exceeded.

Does testosterone raise blood count or cause polycythemia?▼

Testosterone therapy commonly raises hematocrit; polycythemia is a recognized adverse effect requiring dose adjustment, formulation changes, or phlebotomy when thresholds are exceeded.

Body of evidence

Clinical Evidence Brief

RAGMD analyzed 13 relevant studies.

Overall finding

5 studies address hematocrit / erythrocytosis, with weighted findings showing unclear findings. 3 studies address bone mineral density, with weighted findings showing no meaningful effect. 2 studies address sleep-related cognitive symptoms, with weighted findings showing a positive association. 2 studies address venous thromboembolism, with weighted findings showing no meaningful effect. 6 randomized or systematic-review reports and 7 observational studies address treatment. Check hematocrit before initiation and at regular intervals after starting testosterone.

Evidence by outcome

Direction: ↑ Favors treatment / reassuring · ↓ Harm signal · ↔ No clear effect · ± Mixed · ↗ Observational link · ? Unclear

Unclear

Hematocrit / erythrocytosis

moderate · 5 studies

5 studies address hematocrit / erythrocytosis, with weighted findings showing unclear findings. This is an objectively measured outcome. This is a surrogate endpoint and does not by itself prove a hard clinical outcome.

Objectively measured · Surrogate endpoint

Studies

PMID 35467476PMID 34999717PMID 31988219PMID 31495240PMID 25873947
Reassuring

Bone mineral density

high · 3 studies

3 studies address bone mineral density, with weighted findings showing no meaningful effect. This is an objectively measured outcome. This is a surrogate endpoint and does not by itself prove a hard clinical outcome.

Objectively measured · Surrogate endpoint

Studies

PMID 19820017PMID 26901812PMID 11730247
Positive link

Sleep-related cognitive symptoms

high · 2 studies

2 studies address sleep-related cognitive symptoms, with weighted findings showing a positive association.

Mixed measurement

Studies

PMID 34536053PMID 35904664
Reassuring

Venous thromboembolism

moderate · 2 studies

2 studies address venous thromboembolism, with weighted findings showing no meaningful effect. This is an objectively measured outcome. This is a hard clinical endpoint.

Objectively measured · Hard clinical endpoint

Studies

PMID 37326322PMID 26205547
Unclear

Weight / body composition

moderate · 1 study

1 study addresses weight / body composition, with weighted findings showing unclear findings. This is an objectively measured outcome. This is a surrogate endpoint and does not by itself prove a hard clinical outcome.

Objectively measured · Surrogate endpoint

Studies

PMID 35904664
Unclear

Quality of life

moderate · 1 study

1 study addresses quality of life, with weighted findings showing unclear findings. This is a patient-reported / subjective outcome.

Patient-reported

Studies

PMID 35904664

Magnitude / clinical importance

Validated effect estimates in the analyzed set include or 10. Statistical significance is not the same as clinical importance.

Interpret magnitude in absolute terms for the patient in front of you, not from relative estimates alone.

Agreement across studies

Most studies agree on quality of life (unclear findings), while hematocrit / erythrocytosis findings are unclear findings and less consistent across domains.

Supports main conclusion: 1 · Neutral / mixed: 12 · Credible conflicting: 0

Study counts describe the landscape; RAGMD weights studies according to design, quality, and directness.

Conflicting findings

  • Estrogens primarily regulate bone homeostasis in adult men, and testosterone and estradiol levels must decline substantially to impact the skeleton.
  • It has generally been held that estrogen and testosterone are the major sex steroids regulating bone metabolism in women and men, respectively.
  • The results indicated that OSA is significantly correlated with the decrease in serum testosterone levels in men.
  • In men with hypogonadism and preexisting or a high risk of cardiovascular disease, testosterone-replacement therapy was noninferior to placebo with respect to the incidence of major adverse cardiac e…

Risks & harms

4 studies report safety-relevant findings. Design mix: Randomized controlled trial, Study design not clearly classified, Narrative review. Rare-event inference should not rest on underpowered trials alone.

Who this applies to

Most studies included hypogonadal men.

What remains uncertain

  • Optimal hematocrit monitoring thresholds and phlebotomy triggers vary by guideline, formulation, and patient comorbidity.
  • Optimal hematocrit monitoring thresholds and phlebotomy triggers vary by guideline, formulation, and patient comorbidity.

Clinical takeaway

Check hematocrit before initiation and at regular intervals after starting testosterone. When hematocrit exceeds guideline thresholds, address dose, formulation, sleep apnea, and hydration before reflexively stopping a beneficial therapy; phlebotomy or formulation change is often sufficient.

Unclear

Hematocrit / erythrocytosis?

Unclear findings

moderate[35467476 · 34999717 · 31988219 · 31495240 · 25873947]

Reassuring

Bone mineral density?

No meaningful effect

high[19820017 · 26901812 · 11730247]

Positive link

Sleep-related cognitive symptoms?

A positive association

high[34536053 · 35904664]

Reassuring

Venous thromboembolism?

No meaningful effect

moderate[37326322 · 26205547]

Unclear

Weight / body composition?

Unclear findings

moderate[35904664]

Unclear

Quality of life?

Unclear findings

moderate[35904664]

Reassuring

Fractures?

No meaningful effect

moderate[19820017]

Unclear

Fertility / spermatogenesis?

Unclear findings

limited[27855957]

6 randomized or systematic-review reports and 7 observational studies address treatment. Weighted treatment findings show mixed findings.

6 RCT / systematic review · 7 observational

Large randomized trials strongly influence the conclusion

2 landmark studies with randomized or systematic-review designs strongly inform this conclusion.

Supporting studies provide additional context

12 supporting studies add context beyond the core evidence base.

Regimen & duration

Observational and supporting studies provide context and do not outrank higher-appropriateness designs.

Long-term uncertainty

Evidence beyond long follow-up windows and in certain subgroups remains less complete.

14 analyzed studies

Strongest evidence

The aging male : the official journal of the International Society for the Study of the Aging Male2022

Landmark studyPMID 35467476

The HEAT-Registry (HEmatopoietic Affection by Testosterone): comparison of a transdermal gel vs long-acting intramuscular testosterone undecanoate in hypogonadal men.

T substitution with intramuscular TU or T gel increase T concentrations effectively. Long-acting TU leads to a higher rate of hematocrit levels >50%, whilst at the same time it seems to be more efficient to ameliorate anemia in the subgroup of respectively affected hypogonadal patients .

Study
Evidence
Relevance
The New England journal of medicine2023

Landmark studyPMID 37326322

Cardiovascular Safety of Testosterone-Replacement Therapy.

In men with hypogonadism and preexisting or a high risk of cardiovascular disease, testosterone-replacement therapy was noninferior to placebo with respect to the incidence of major adverse cardiac events. (Funded by AbbVie and others; TRAVERSE ClinicalTrials.gov number, NCT03518034.).

RCT
Evidence
Relevance

Supporting literature

Association between obstructive sleep apnea and male serum testosterone: A systematic review and meta-analysis.

Obstructive sleep apnea and serum total testosterone: a system review and meta-analysis.

Effects of aromatase inhibition on bone mineral density and bone turnover in older men with low testosterone levels.

+9 more

More in this focus area

Related evidence analyses

Other structured clinical questions in Men's Hormone Health.

Does testosterone replacement increase cardiovascular risk?

Large randomized data (including TRAVERSE) do not show a significant increase in major adverse cardiovascular events with testosterone therapy in hypogonadal men over median follow-up of roughly three years. Older observational studies conflict, and absolute risk depends on baseline cardiovascular disease, formulation, and monitoring.

11 linked studies

Does testosterone therapy increase prostate cancer risk?

Current systematic reviews and trial secondary analyses do not show a convincing increase in prostate cancer incidence among hypogonadal men treated with testosterone, though surveillance remains standard practice.

14 linked studies

Does testosterone therapy suppress fertility in men?

Exogenous testosterone suppresses the hypothalamic-pituitary-gonadal axis and reliably reduces spermatogenesis. Recovery after discontinuation is variable and may be incomplete in some men.

14 linked studies

Does testosterone therapy increase venous thromboembolism risk?

Large observational cohorts suggest a modest increase in venous thromboembolism risk with testosterone therapy, particularly early after initiation. Absolute risk remains low in most populations but warrants attention in predisposed patients.

14 linked studies

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