Reasoning GP · Algorithm · 1-page summary
Thrombocytopenia — low platelet count
For: adults with platelets <150 × 10⁹/L on an FBC, well or unwell, including pregnancy (block 2). Not for: children (use paediatric pathways). Local haematology pathway sets thresholds and repeat intervals.
Core rule: the count alone does not set bleeding risk or urgency. Bleeding, a rapid fall, other cytopenias or a haemolytic (TTP) picture do. Never delay urgent referral to exclude pseudothrombocytopenia.
0Stop — call 999 now — at any platelet count
- Major bleeding (GI, haemoptysis, heavy haematuria, retinal) or severe headache, confusion, focal weakness, seizures, reduced consciousness (ICH, TTP) → 999
- TTP/TMA: low platelets + haemolysis (schistocytes, raised LDH, low haptoglobin) ± neurological, renal, cardiac or GI features → Emergency discussion with the regional TTP/haematology service. Do not wait for the pentad or ADAMTS13.
- DIC (bleeding from several sites, hypotension, confusion); non-blanching rash with fever or unwell; HIT with thrombosis → 999. Pregnant with hypertension, headache, visual change or epigastric pain → Emergency obstetric (pre-eclampsia/HELLP).
- While waiting: suspected HIT → stop all heparin (including flushes). Do not stop anticoagulants or antiplatelets automatically — discuss. No routine platelet transfusion in ITP, HIT or TTP.
1Triage by count — × 10⁹/L, if block 0 is negative
| Platelets | Action |
|---|---|
| <20 or falling fast | Same-day haematology even without bleeding (especially <10) |
| <50 unexplained | Same-day haematology |
| 50–100 | Investigate; discuss or refer per local pathway, especially if new, falling or symptomatic |
| 100–150 | Isolated, stable, well, no atypical features → primary care: repeat FBC + film; discuss if persistent, falling or <100 |
2Screen — one row is enough
- Non-blanching petechiae, extensive purpura, gum or nose bleeding → Same-day FBC, film and haematology discussion
- Schistocytes or blasts on film, pancytopenia, clinically significant bleeding → Same-day haematology
- Recent heparin, quinine, antibiotics or chemotherapy + platelet fall → Same-day haematology (drug-induced or HIT); HIT: 4Ts score.
- Pregnant, new, falling or moderate fall → Same-day obstetric/haematology: exclude pre-eclampsia/HELLP, ITP, TTP, acute fatty liver.
3Assess — only once blocks 0–2 are answered
☐ Previous counts, lab comment ☐ Repeat FBC + film ☐ Obs; skin, mucosa, spleen, liver, nodes ☐ Clotting + fibrinogen if DIC, liver disease or bleeding ☐ LFT, reticulocytes, LDH, haptoglobin ☐ Drugs, alcohol, recent viral illness
Suspected ITP: HIV, hepatitis B/C, ANA, immunoglobulins per context. Pseudothrombocytopenia: only in a well patient without bleeding — citrate sample if clumping. Not in primary care: bone marrow biopsy, antiplatelet antibodies.
4Classify — read the film
- Clumps, well patient — pseudothrombocytopenia (EDTA artefact) → citrate count; no treatment.
- Isolated, normal Hb/WCC — ITP (diagnosis of exclusion, haematology-confirmed), drugs, alcohol/liver, viral. Marrow disease not excluded.
- Other cytopenias — marrow (MDS, leukaemia, aplasia), B12 deficiency, hypersplenism → pancytopenia is Same-day.
- Gestational — only if late, isolated, no hypertension or proteinuria, normal LFTs and haemolysis markers, no bleeding or past ITP.
- Post-viral — recovering on repeat; escalate if falling, symptomatic or other lines affected.
- Uncertain — persistent, unexplained after initial tests → haematology.
5Treat today — only these
- Suspected culprit drug: stopping may be right, but not an essential medicine without an alternative. HIT needs a non-heparin anticoagulant.
- Avoid NSAIDs/aspirin with significant thrombocytopenia or bleeding unless haematology advises; paracetamol instead. Reduce alcohol.
- ITP: observe or treat (steroids, IVIg) is a haematology decision. Doses: NICE/SPC, BNF, local formulary.
6Refer routinely
- <100, persistent or falling; splenomegaly; dysplasia on film; B symptoms → discuss or refer per local pathway.
- Suspected or known ITP → haematology (confirmation and management are haematology-led).
- Surgery, dental work, IM injection, neuraxial anaesthesia → agree thresholds with haematology.
- Splenectomy → vaccinate ideally ≥2 weeks before (Green Book ch 7 and 25).
7Never reassure by
- A count above a "safe" number — a rapid fall matters more.
- Calling it EDTA artefact with bleeding, other cytopenias or an abnormal film.
- Waiting for the full TTP pentad or an ADAMTS13 result.
- Calling it gestational before pre-eclampsia/HELLP is excluded.
- Stopping heparin alone in suspected HIT.
- Normal Hb and WCC — marrow disease is not excluded.
8Safety-net — say it, then document it
999 “Call 999 for a severe headache, weakness, a fit or confusion; vomiting blood or black stools; coughing blood or severe breathlessness; sudden loss of vision; bleeding from several places; heavy blood in the urine or feeling faint; or a rash that does not fade under pressure with a fever.” Pregnant: severe headache, vision changes or upper abdominal pain → emergency maternity.
Same day “New spreading spots or bruises, a nosebleed not stopping after 10–15 minutes of pressure (go to A&E), soaking a pad every hour, gums that keep bleeding, or blood in the urine — contact us today.” Any bleeding with platelets <20 is same-day. Follow-up: repeat FBC + film; re-refer if falling, new bleeding or <20.
✓Safe to leave primary care only if — all five, documented
No block 0–2 feature; no bleeding
Count confirmed on repeat with film; not falling
Isolated: normal Hb, WCC and film; no splenomegaly
Drugs, alcohol and pregnancy checked
Repeat FBC dated; safety-net given
Summary of the full Reasoning GP thrombocytopenia algorithm, which holds the detail, examination, investigations and evidence. Sources: BSH TTP and other TMAs (2023); BSH HIT (2024); NICE NG24, NG240, NG253, NG133, NG12 (updated April 2026); International Consensus Report on ITP (2019); UKHSA Green Book chapters 7 and 25; local haematology pathway. Clinical reference — follow local pathways and check doses: NICE/SPC, BNF.