CLL (Chronic Lymphocytic Leukaemia) is the most common adult leukaemia in the Western world — it presents as an incidental finding of lymphocytosis on routine FBC in approximately 70% of cases. The blood film is diagnostic: smear cells (Gumprecht shadows or smudge cells — ruptured CLL lymphocytes that are mechanically fragile and disintegrate when spread on the slide) are highly characteristic of CLL and distinguish it from reactive lymphocytosis where the cells are intact. The CLL diagnosis requires: persistent lymphocytosis above 5 × 10⁹/L + monoclonal B-lymphocytes (confirmed by flow cytometry showing CD5+/CD19+/CD23+ co-expression — the classic CLL immunophenotype). The majority of CLL patients are elderly (median age at diagnosis 72) and have indolent disease that requires no treatment initially — 'watchful waiting' (active monitoring without treatment) is appropriate for Binet stage A or B disease without symptoms. The GP's role: arrange haematology referral, provide reassurance that CLL is often slow-growing, and avoid over-alarming the patient.

Pertussis (whooping cough) classically causes a very pronounced lymphocytosis — absolute lymphocyte counts of 15-30 × 10⁹/L are characteristic and are caused by pertussis toxin inhibiting lymphocyte migration out of the blood into lymphoid tissue (the cells accumulate in peripheral blood). This lymphocytosis pattern in a child or unvaccinated adult with a prolonged cough (the catarrhal phase lasting 1-2 weeks, followed by the paroxysmal phase with inspiratory whoop) should prompt consideration of pertussis. The nasopharyngeal swab or PCR is the diagnostic test in the first 3 weeks; serology (pertussis IgG) after 3 weeks. Treatment: azithromycin 500 mg OD x 5 days (reduces transmission, minimal effect on illness duration if paroxysmal phase already begun). Pertussis is a notifiable disease — notify PHE. The whooping cough immunisation programme (DTaP at 8, 12, 16 weeks; pre-school booster; maternal vaccination at 16-32 weeks of pregnancy) has significantly reduced but not eliminated pertussis. Large granular lymphocyte (LGL) leukaemia is another important and frequently delayed diagnosis — the triad of: neutropenia (recurrent bacterial infections) + splenomegaly + positive RF/ANA in a middle-aged adult = LGL leukaemia until haematology assessment proves otherwise.

Flow cytometry for lymphocyte immunophenotyping is the gold standard investigation for distinguishing reactive from clonal lymphocytosis — it measures the surface antigen profile of lymphocytes, identifying: clonal B-cell populations (CD5+/CD19+/CD23+ = CLL; CD5+/CD19+/cyclin D1+ = mantle cell lymphoma; CD10+ = follicular lymphoma), T-cell receptor clonality (T-LGL), and the ratio of kappa to lambda immunoglobulin light chains on B-cells (a kappa:lambda ratio above 10:1 or below 0.5:1 = monoclonal = malignant). This test is arranged by haematology following referral — it cannot be requested directly from primary care in most centres. GPs should refer promptly when the blood film and clinical picture suggest clonal lymphocytosis, rather than waiting further — early haematology assessment allows proper characterisation and staging, which determines management (watchful waiting vs treatment initiation).

The CLL watchful waiting approach requires specific patient communication skills — patients who are told they have 'leukaemia' but are then told nothing will be done about it understandably find this distressing and confusing. The key explanation: 'CLL is a type of blood cancer, but it behaves very differently from most cancers. In most people, it grows very slowly — so slowly that we can watch it for years, or even decades, without needing to treat it. The research shows clearly that treating it early (when it is not causing symptoms) does not help and can harm — it does not extend life or prevent the disease from progressing. We will monitor you closely with regular blood tests, and the moment it starts to cause symptoms or affect your other blood cells, we will act.' This reframing of 'watchful waiting' as active evidence-based management (not neglect) significantly improves patient acceptance. Many CLL patients live normal lives for 10-15 years without ever needing treatment.

The pertussis notification obligation for GPs is a legal requirement under UK public health legislation — pertussis is a notifiable disease and GPs who suspect or diagnose pertussis must notify the local Health Protection Team (HPT) by telephone as soon as the diagnosis is made (not waiting for laboratory confirmation). The UK still experiences significant pertussis outbreaks — approximately 5,000-10,000 confirmed cases per year. The maternal pertussis vaccination programme (Boostrix-IPV vaccine at 16-32 weeks gestation) has dramatically reduced infant pertussis deaths by providing passive immunity to newborns before their own vaccination at 8 weeks. GPs who identify pertussis in a pregnant woman or a close contact of a newborn should: notify PHE, arrange azithromycin post-exposure prophylaxis for close contacts, and notify obstetric team.

EBV infectious mononucleosis post-acute fatigue is one of the most important patient communication challenges in primary care — approximately 10-15% of patients with EBV mononucleosis develop prolonged fatigue lasting 3-12 months after the acute illness (post-infectious fatigue syndrome). A subset meets the criteria for chronic fatigue syndrome/myalgic encephalomyelitis (CFS/ME — estimated prevalence of CFS/ME following EBV is approximately 10-fold higher than the general population). GPs should: (1) at the initial consultation, warn patients that a period of prolonged fatigue is possible after EBV; (2) avoid reassurance that they will 'be back to normal in 2 weeks' — this creates unrealistic expectations that damage the patient-GP relationship when prolonged fatigue develops; (3) arrange FBC + LFTs at 6-8 weeks to confirm resolution of acute haematological changes; (4) screen with PHQ-9 (depression is a common co-morbidity in prolonged post-EBV fatigue); (5) refer to CFS/ME specialist services if fatigue persists beyond 3 months with significant functional impairment.

The CLL vaccination strategy requires specific planning — patients with CLL are immunosuppressed (particularly those who have received treatment) and should receive: annual influenza vaccine (inactivated IM), pneumococcal vaccines (PCV13 + PPV23), COVID-19 boosters, Shingrix (recombinant zoster), and hepatitis B vaccine if not immune. However, vaccine responses may be suboptimal because CLL B-cells cannot produce adequate antibody responses to vaccine antigens. BCSH guidelines recommend measuring antibody responses to vaccines (anti-pneumococcal IgG, anti-HBs) in CLL patients to confirm adequate protection. Patients who fail to respond to standard doses may benefit from higher-dose or repeat vaccination schedules. Live vaccines (MMR, yellow fever, varicella/ZVL) are contraindicated in all CLL patients regardless of treatment status.

The CLL and skin cancer connection is clinically important and frequently underemphasised — CLL patients have approximately 8-10 times the general population risk of squamous cell carcinoma (SCC) of the skin, driven by: T-cell immune surveillance impairment (failing to eliminate UV-damaged keratinocytes), B-cell immune abnormalities, and treatment-related immunosuppression. GPs monitoring CLL patients in watchful waiting should incorporate: an annual skin examination (full body, including sun-exposed areas), advice about daily SPF50+ sunscreen and sun protection clothing, prompt biopsy of any non-healing, crusting, or growing skin lesion. Dermatology referral (2WW if suspicious) for any concerning skin lesion in a CLL patient. The management of SCC in immunosuppressed patients is more aggressive than in immunocompetent patients because of the significantly higher risk of metastasis.

The blood film documentation principle for CLL: once smear cells are identified on a blood film, this is the key discriminating morphological finding that should trigger haematology referral — smear cells (Gumprecht shadows) represent fragile CLL lymphocytes that rupture during the preparation of the blood film, leaving only the nuclear remnant as a smear on the slide. They are highly characteristic of CLL and are found in approximately 95% of CLL cases on film review. Any patient whose routine FBC and blood film is reported as showing 'smear cells' without a prior CLL diagnosis should be referred to haematology for flow cytometry and staging, even if the absolute lymphocyte count is in the MBL range (3-5 × 10⁹/L). The finding of smear cells is a morphological cue to request haematology assessment — it is not a wait-and-watch result.