Reasoning GP · Algorithm · 1-page summary
Testosterone deficiency in men
For: adult men with symptoms of testosterone deficiency (TD) or a low testosterone result, in primary care, before and during testosterone therapy (TRT). Not for: women or children; breast enlargement (use the gynaecomastia algorithm). TRT is started only under a documented local endocrine/urology shared-care protocol.
Core rule: one low level is not enough — diagnose only with symptoms plus two 7–11am testosterone levels and LH/FSH. Never start TRT in secondary TD before endocrine assessment, or in a man who may want children.
0Stop — call 999 now
- Severe chest pain, severe breathlessness, face or throat swelling or collapse during or after a Nebido injection (POME or anaphylaxis) 999
- Sudden severe headache with visual loss (possible pituitary apoplexy) · suspected adrenal crisis (vomiting, low blood pressure, collapse) in hypopituitarism 999
1Triage — total testosterone (TT), two 7–11am samples
| TT result | Meaning → next step |
|---|---|
| Single, afternoon or ill | Not diagnostic → repeat ×2, 7–11am, ~4 weeks apart, avoid acute illness |
| <8 nmol/L ×2 | Strongly supports TD if symptomatic → LH, FSH, FBC; prolactin if LH/FSH low or inappropriately normal |
| 8–12 nmol/L | Borderline → SHBG and calculated free testosterone |
| >12 nmol/L | TD less likely, though context matters |
BSSM action thresholds, not universal cut-offs — use the local assay and reference range.
2Screen — before any TRT
- TT <5.2 nmol/L + low LH/FSH, raised prolactin, visual or neurological symptoms, other pituitary-axis abnormalities → Urgent endocrinology; consider pituitary MRI. No TRT alone.
- Prostate feels malignant on DRE → refer Suspected cancer pathway (NG12). PSA above age threshold with possible prostate symptoms (40–49 >2.5; 50–59 >3.5; 60–69 >4.5; 70–79 >6.5 microgram/L) → consider the same route. No testosterone until resolved.
- Low testosterone + anaemia + bone pain + fatigue, especially in an older man → exclude myeloma and prostate bone metastases before any TRT.
- Low LH/FSH with liver disease, diabetes, arthropathy or bronze skin → ferritin and transferrin saturation Urgent (haemochromatosis).
- Fertility wanted now or in future, haematocrit >54% or severe heart failure (NYHA IV) → do not start TRT.
3Assess
Screen: ED, loss of morning erections or low desire; T2DM, CKD, BMI >30 or waist >102 cm; long-term opiates, antipsychotics, anticonvulsants.
☐ Testes, BMI, breasts ☐ Ask directly about anabolic steroids ☐ STOP-BANG ☐ Mood (depression mimics TD) ☐ FBC/haematocrit, TSH, HbA1c, LFT + ferritin, CV risk ☐ PSA per local protocol; DRE if indicated
4Classify — LH is the branch point
- Primary — high LH/FSH: Klinefelter (small firm testes → karyotype), orchitis, chemo/radiotherapy, trauma. No pituitary work-up needed.
- Secondary — low or inappropriately normal LH: prolactinoma, pituitary disease, opioids, glucocorticoids, anabolic steroids, haemochromatosis → endocrine assessment before TRT.
- Functional — obesity, T2DM, OSA, alcohol, opioids, systemic illness → correct the cause first.
- Late-onset — symptoms + confirmed deficiency, reversible causes excluded; many older men need no treatment.
- Uncertain — borderline TT or symptoms only → free testosterone, treat functional causes, reassess; symptoms alone never justify TRT.
5Treat today
- Functional: weight loss, treat OSA (CPAP), alcohol ≤14 units/week, opioid review (consider buprenorphine), stop anabolic steroids. No supplements to raise testosterone.
- ED: a PDE5 inhibitor remains first line after the usual checks (nitrates, CV disease); TRT is not an ED treatment.
- TRT only for confirmed TD, no contraindication, under the local protocol: counsel on fertility, prostate, polycythaemia; gel — wash hands, cover site; Nebido — observe ~30 min. Doses: NICE/SPC, BNF, local formulary.
- On TRT (3, 6, 12 months, then yearly): haematocrit 0.50–0.54 → consider dose cut; ≥0.54 → withhold or reduce + specialist advice. PSA rise >1.4 ng/mL in 12 months or >0.4 ng/mL/year over >2 years → urology. No benefit by 6 months → review, look for other causes.
6Refer routinely
- Reproductive endocrinology / andrology: fertility wanted — before any TRT; stop TRT if new wish for children.
- Endocrinology: primary TD without a GP pathway, Klinefelter, borderline or complex cases, previous prostate cancer, persistent suppression after anabolic steroids.
7Never reassure by
- A single, afternoon or private testosterone result.
- A "normal" LH — inappropriately normal LH with low TT is secondary TD.
- "Children in a couple of years" — that man is not a TRT candidate.
- Low mood and fatigue alone — depression, OSA, hypothyroidism mimic TD.
- Good testosterone levels on TRT while haematocrit or PSA climbs.
- Repeat prescriptions — TRT needs a documented annual review.
8Safety-net — say it, then document it
999 “Severe chest pain or breathlessness, face or throat swelling or collapse during or after your injection, or a sudden severe headache with loss of vision — call 999.” Same day “Milder cough or breathlessness after the injection that is settling, severe breast swelling or pain, or new aggression or very high mood — contact us today.”
Review: two morning levels before any decision; on TRT at 3, 6 and 12 months, then a formal yearly review.
✓Safe to manage in primary care only if — all five, documented
No block 0–2 row applies
Two 7–11am levels + LH/FSH (prolactin if indicated)
Fertility wishes asked and documented
Prostate, haematocrit, CV risk and OSA assessed
Safety-net and monitoring dates given
Summary of the full Reasoning GP testosterone deficiency algorithm, which holds the detail, preparations, monitoring schedule and evidence. Sources: BSSM 2023 (Hackett et al.); NICE NG12 (updated April 2026); EAU Sexual and Reproductive Health; Nebido SPC; NOGG 2022. BSSM thresholds are society recommendations, not NICE requirements. Clinical reference — follow your local endocrine/urology shared-care protocol and check doses: NICE/SPC, BNF.