Reasoning GP · Algorithm · 1-page summary
Polycythaemia — persistent erythrocytosis
For: adults in primary care with a raised haemoglobin or haematocrit (Hct). Not for: a raised platelet count alone (use the thrombocytosis algorithm); known PV on treatment follows the haematology plan and shared-care protocol.
Core rule: a raised Hct is an investigation threshold, not a diagnosis of polycythaemia vera (PV). Confirm it persists on a venous repeat, then check EPO and JAK2. Never venesect, or start aspirin for a raised Hct, in primary care.
0Stop — call 999 now — with any raised Hct
- Stroke or TIA symptoms, focal neurology, confusion, seizure or reduced consciousness → 999
- Chest pain suggesting ACS; suspected PE with significant symptoms or instability; severe breathlessness or hypoxia → 999
- Severe abdominal pain, ascites or liver decompensation (acute Budd–Chiari, hepatic vein thrombosis) → 999
- While waiting: management depends on the diagnosis, haemodynamic state, bleeding risk and specialist advice. Do not venesect in primary care.
1Triage by venous Hct
| Result | Action |
|---|---|
| Single raised Hct | Look for dehydration, acute illness, diuretics, alcohol, smoking or CO; repeat venous FBC + film (interval per local pathway). |
| >0.52 men >0.48 women | Persistent → investigate (block 3). Do not keep deferring. |
| ≥0.60 men ≥0.56 women | Prompt clinical assessment; Same-day haematology if symptoms, thrombosis, pregnancy or other major count abnormalities. |
Hct beats Hb. If Hb is used: WHO >165 g/L men, >160 g/L women. Hct is higher at altitude.
2Screen — serious causes
- Severe headache, visual disturbance or dizziness (possible hyperviscosity) → Same-day specialist discussion; do not wait for JAK2
- Recent thrombosis with marked Hct; pregnancy with known or suspected PV; film suggesting leukaemia or transformation; severe thrombocytosis or leucocytosis → Same-day haematology
- Suspected DVT → Same-day assessment (NG158)
- Splenomegaly → Urgent haematology discussion; same-day if symptomatic or marked high WCC/platelets
- Positive JAK2; low EPO with negative JAK2; high WCC or platelets; any thrombosis; young-onset or lifelong; progressive night sweats or weight loss → Urgent haematology
3Assess
☐ Repeat FBC + film, U&E, LFT, calcium; ferritin if microcytic ☐ Serum EPO + JAK2 V617F per local pathway ☐ SaO₂; carboxyhaemoglobin if smoker or CO exposure ☐ BP, spleen, cyanosis, clubbing, chest, legs ☐ Drugs: testosterone, anabolic steroids, EPO, diuretics ☐ Spirometry if COPD suspected; sleep pathway if OSA suspected
Renal ultrasound only if EPO raised, haematuria, renal disease or transplant, or no other cause. No bone marrow, routine CT or AFP in primary care.
4Classify
- Relative (low plasma volume): dehydration, diuretics, smoking, obesity, alcohol → address, repeat; no venesection.
- Secondary — hypoxic: COPD, OSA, smoking, altitude, cyanotic heart disease; normal daytime SaO₂ does not exclude night hypoxia → treat the cause.
- Secondary — other: renal disease or transplant, EPO-secreting tumour (RCC, HCC), testosterone, anabolic steroids, EPO → review drugs; imaging as block 3.
- PV (clonal): JAK2 in ~95%, EPO low or normal, splenomegaly, high platelets/WCC, itch after bathing, erythromelalgia, thrombosis → urgent haematology.
- Uncertain — persistent and unexplained → EPO/JAK2 or haematology advice.
5Treat today — only these
- Smoking: behavioural support with varenicline, cytisinicline, combination NRT or a nicotine vape (NG209).
- Avoid dehydration with normal fluid intake, adjusted for heart or kidney disease; review diuretics and testosterone.
- Cardiovascular risk: BP, statin per NICE; weight support; treat COPD; OSA via sleep pathway.
- No aspirin solely for a raised Hct. Known PV: haematology plan (venesection to Hct <0.45, aspirin unless contraindicated); hydroxycarbamide only under local shared care.
6Refer routinely
- Haematology advice and guidance (local): borderline persistent Hct with normal EPO and negative JAK2; family history.
- Respiratory / sleep: hypoxic lung disease, suspected OSA. Nephrology: polycystic kidneys, post-transplant, renal artery stenosis.
- Pregnancy planning with PV → early haematology and obstetric review.
- Known PV — re-refer: Hct rising despite venesection, thrombosis on treatment, hydroxycarbamide intolerance.
7Never reassure by
- Repeating the FBC again and again instead of investigating persistence.
- A negative JAK2 — it does not prove relative erythrocytosis.
- Normal daytime oximetry — misses night hypoxia and carboxyhaemoglobin.
- "Gaisböck syndrome" from obesity and high BP alone.
- Treating a positive JAK2 as a PV label, or starting treatment yourself.
- "It's just smoking" — if it persists after stopping, investigate.
8Safety-net — say it, then document it
999 “Call 999 for a sudden severe headache, face or arm weakness or speech problems, even if they go away; chest pain or sudden breathlessness; severe tummy pain with swelling; confusion or a fit.” Same day “Contact us today if one leg becomes swollen or painful, you get headaches with blurred vision, a swelling or discomfort under your left ribs, unusual bleeding, or you are pregnant and have PV.”
Remote result: Hct ≥0.60 men / ≥0.56 women → prompt clinical assessment, same-day if any symptoms; do not file it as routine.
✓Safe to manage in primary care only if — all five, documented
No block 0–2 row applies; patient well
Persistence checked on a venous repeat
EPO + JAK2 sent, or haematology advice
Smoking, fluids and drugs addressed
Recheck dated, safety-net given
Summary of the full Reasoning GP polycythaemia algorithm, which holds PV treatment, cytoreduction, monitoring and evidence. Sources: BSH guidelines on PV and on secondary erythrocytosis (2019); WHO classification of myeloid neoplasms; NICE TA921, NG209, NG158; local hydroxycarbamide shared-care protocol. Clinical reference — follow local pathways and check doses: NICE/SPC, BNF.