A 73-year-old male presents to the GP for review after some recent blood tests. He has been feeling fatigued and dizzy for the past 2 weeks, which prompted the initial investigation. His past medical history includes COPD and he is currently taking triple therapy for this. He has recently been investigated for Long Term oxygen Therapy, but did not qualify due to a pO2 of 7.5kPa. His blood tests show:


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|--------------|:-------:|---------------|
|Haemoglobin|201 g/L|(M) 130 - 170, (F) 115 - 155|
|White Cell Count|4.2x10<sup>9</sup>/L|3.0 - 10.0|
|Platelets|350x10<sup>9</sup>/L|150 - 400|
|Mean Cell Volume (MCV)|90 fL|80 - 96|


Which of the following is the most likely diagnosis?

Options:
explanation: This is incorrect because primary polycythaemia is due to the spontaneous proliferation of red blood cells in the bone marrow. This is less likely, though is an important differential, given the normal platelet and white cell count, which are also usually deranged in polycythaemia rubra vera, and an otherwise clear and logical explanation ie. chronic hypoxia in COPD. There is also no history of itching on hot baths, which is more likely in polycythaemia rubra vera.
name: Primary polycythaemia
label: b
answer: no
explanation: Blood tests show a raised haemoglobin, which is suggestive of polycythaemia. This patient has got a disorder (COPD) leading to chronic hypoxia, and as a result has developed secondary polycythaemia. Primary polycythaemia, such as polycythaemia rubra vera, indicates a primary bone marrow disorder, and given the normal platelet and white cell count values, this is less likely, though an important differential. There is also no history of itching on hot baths, which is more likely in polycythaemia rubra vera.  It is important to note that a pO2 of <7.3 is the usual criteria for LTOT, but between 7.3-8 he would qualify if he had complications related to chronic hypoxia, such as polycythaemia. He would now most likely fuflfil LTOT criteria, and referral back to the LTOT service will be indicated. Symptoms of polycythaemia include dizziness and fatigue.
name: Secondary polycythaemia
label: a
answer: yes
explanation: Myelofibrosis presents with constitutional symptoms such as fatigue, weight loss, fever, and night sweats, alongside splenomegaly. Blood tests show potential pancytopenia due to bone marrow failure secondary to fibrosis, which usually results in dry taps during bone marrow aspiration. Blood film findings are tear-drop poikilocytes.
name: Myelofibrosis
label: c
answer: no
explanation: Essential thrombocythaemia is a myeloproliferative disorder characterised by an increased number of platelets in the blood. This patient's platelet levels are within the normal range. It is associated with proliferation of megakaryocytes (platelet precursors.)
name: Essential thrombocythaemia
label: e
answer: no
explanation: Patients with CLL are usually diagnosed incidentally after finding a raised white cell count, and specifically lymphocytes, on blood tests. The white cell count is normal in this patient. Patients with CLL may present with lymphadenopathy, hepatosplenomegaly, and constitutional symptoms. It is important to remember the blood film finding for CLL which can show smudge cells as they become damaged due to the lack of a cytoskeletal protein.
name: Chronic lymphocytic leukaemia
label: d
answer: no

Correct answer: a


Learning point: Secondary polycythaemia is a condition characterized by an increased number of red blood cells in response to chronic low oxygen levels or other underlying conditions, such as lung disease or tumors that produce erythropoietin.