Neutropenic sepsis is the most time-critical emergency arising from pancytopenia — an absolute neutrophil count (ANC) below 0.5 × 10⁹/L removes virtually all the body's capacity for bacterial killing. Normal bacterial infection is contained by neutrophil phagocytosis at the site of entry (skin, gut, respiratory tract) — without neutrophils, bacteria that would normally cause a localised cellulitis instead rapidly cause bacteraemia and septicaemia with minimal localising signs. This means neutropenic patients develop systemic sepsis from organisms and from sites (particularly gut translocation of gram-negative bacteria) that would be innocuous in an immunocompetent person. The clinical implication: any febrile patient with known or suspected neutropenia (ANC <0.5) should be treated as neutropenic sepsis until proved otherwise — broad-spectrum antibiotics within 1 hour regardless of the apparent severity of presentation. The UK Oncology Nursing Society (UKONS) neutropenic sepsis pathway specifies piperacillin-tazobactam (Tazocin) 4.5 g IV every 8 hours as first-line in most centres.

Aplastic anaemia is the paradigm case of immune-mediated bone marrow failure — in approximately 70% of cases it is idiopathic, but the mechanism is now understood to involve autoreactive T-cells (particularly CD8+ cytotoxic T-cells secreting IFN-γ and TNF-α) that destroy haematopoietic stem cells in the bone marrow. The clinical significance is that this immune-mediated mechanism makes aplastic anaemia treatable with immunosuppressive therapy (horse anti-thymocyte globulin + ciclosporin — IST) achieving complete or partial remission in approximately 70% of patients who are not eligible for HSCT. HSCT (haematopoietic stem cell transplant) is preferred in patients under 40 with a matched sibling donor — cure rate approximately 85–90%. MDS is particularly important to know as a GP because it presents insidiously in elderly patients with gradually worsening anaemia, fatigue, and recurrent infections — often initially attributed to 'old age' or 'iron deficiency'. The characteristic blood film findings of MDS (dysplastic neutrophils with hypersegmentation or nuclear hypolobulation — pseudo-Pelger-Huët anomaly — and macro-ovalocytes) should trigger urgent haematology referral. Ring sideroblasts on bone marrow iron stain are diagnostic of MDS-RS subtype.

The blood film review is the single most important investigation in the management of unexplained pancytopenia — it is the only test that directly shows the morphology of individual blood cells, which reveals the underlying pathology in the majority of cases. An automated FBC analyser counts cells and measures parameters but cannot identify blast cells (which look like large activated lymphocytes on automated counting), dysplastic changes in neutrophils (which may be counted as normal neutrophils), or abnormal platelet morphology. A haematologist reviewing the blood film within 24 hours of a pancytopenia result should be the standard of care. In practice, this means requesting an urgent blood film review (not just FBC) and writing on the request form: 'Pancytopenia — please review film urgently for blast cells and dysplastic changes.' Many GP requests for FBC do not specifically request blood film review, and the film is only examined automatically when the analyser flags an abnormality — this means subtle dysplastic changes or early blast populations may be missed. The reticulocyte count is also critical: a low reticulocyte count in the context of pancytopenia = bone marrow failure (hypoproliferative — the marrow is not responding to the anaemia); a high reticulocyte count = peripheral destruction or acute haemolysis (the marrow is responding but cells are being lost).

Severe aplastic anaemia (SAA) has specific diagnostic criteria that determine management urgency: ANC <0.5 × 10⁹/L + platelets <20 × 10⁹/L + reticulocytes <20 × 10⁹/L + hypocellular bone marrow. Very severe aplastic anaemia (vSAA): ANC <0.2 × 10⁹/L. The distinction matters because: SAA and vSAA require urgent treatment (HSCT or IST within weeks) and have a mortality of approximately 70–80% without treatment (historically). With modern treatment (HSCT in eligible patients, IST for others): 5-year survival is approximately 75–85%. The GP's role when pancytopenia is identified on a routine FBC: examine the result holistically (all three cell lines), request blood film, check B12/folate, and determine urgency by the severity of the lowest count and the presence or absence of symptoms (bleeding, infections).

The clozapine monitoring programme is a mandatory pharmacovigilance system that GPs may be involved in — clozapine (an atypical antipsychotic used for treatment-resistant schizophrenia) causes agranulocytosis in approximately 0.8% of patients, with a peak risk in the first 18 weeks. The Clozaril Patient Monitoring Service (CPMS) or equivalent system requires mandatory FBC monitoring: weekly for the first 18 weeks, then 2-weekly for 12 months, then monthly. No new prescription of clozapine can be dispensed without a current normal blood count. GPs who receive FBC results for clozapine patients must act on any neutropenia: ANC 1.5–2.0 = amber (increased monitoring frequency); ANC <1.5 = red (clozapine must be stopped immediately and haematology notified). Never stop and restart clozapine after agranulocytosis — permanent rechallenge is contraindicated.

The eltrombopag addition to the standard IST regimen for aplastic anaemia (the RACE trial, NEJM 2022) represents a major advance in aplastic anaemia treatment — eltrombopag is a thrombopoietin receptor agonist that stimulates haematopoietic stem cell proliferation. When added to hATG + ciclosporin, the complete response rate at 6 months improved from approximately 40% to 68% in the RACE trial, with faster platelet recovery. Eltrombopag is now standard first-line for aplastic anaemia alongside IST at most UK haematology centres. GPs managing patients with aplastic anaemia in shared care should know that eltrombopag (Revolade) is the thrombopoietin agonist used — it requires monitoring for liver toxicity (LFTs monthly) and cataract risk (annual ophthalmology if on long-term treatment).

The irradiated blood products requirement for patients with aplastic anaemia, haematological malignancy, or post-HSCT is a critical blood transfusion safety principle — transfusion-associated graft-versus-host disease (TA-GvHD) occurs when viable donor T-lymphocytes in non-irradiated blood products engraft in a severely immunocompromised recipient and attack the host's tissues. TA-GvHD has a mortality of approximately 90–100% and is entirely preventable by irradiating blood products before transfusion (gamma-irradiation kills donor lymphocytes without damaging red cells or platelets). GPs ordering blood transfusions or receiving patients recently discharged from haematology with blood product requirements must ensure the blood requirement documentation specifies 'irradiated' where indicated — this is a GP prescribing responsibility in shared care contexts.

Fertility preservation before chemotherapy or HSCT is one of the most important quality-of-life interventions in haematological oncology, and GPs play a role in the pre-treatment phase — NICE recommends that all patients of reproductive age who are about to receive gonadotoxic treatment (alkylating agents particularly: cyclophosphamide, busulfan, melphalan — all used in HSCT conditioning) should be offered urgent fertility preservation. For women: emergency ovarian stimulation and oocyte/embryo cryopreservation (takes approximately 2 weeks — timing with chemotherapy start is critical). For men: semen cryopreservation (takes 1–2 days — straightforward, should never be missed). The haematology team should arrange this, but GPs who identify haematological malignancy or aplastic anaemia in a young patient should proactively ask whether fertility preservation has been discussed and documented.

The post-IST relapse rate in aplastic anaemia (~35% within 3 years) is a crucial follow-up point for GPs — patients who have achieved complete or partial remission with IST (hATG + ciclosporin) and who are in shared care will have declining ciclosporin doses over 12–24 months. As the immunosuppression is reduced, a subset of patients relapse (pancytopenia returns). The clinical signal is a gradual fall in one or more cell lines on serial FBCs, often beginning before the patient develops symptoms. GPs in shared care who are ordering routine monitoring FBCs for aplastic anaemia patients must compare results to previous values and refer back to haematology if any downward trend is identified. Early re-treatment of relapse with a second IST course or HSCT (if now eligible) achieves high remission rates — delayed relapse recognition leads to more serious bone marrow failure requiring emergency management.