• About: Hb depends on sex and age. Look at Hb, MCV and MCH. Anaemia may be acute or chronic but is better tolerated in young. Anaemia Hb <130 g/L in men, 120 g/L in women, 110 g/L pregnant women.
  
• Pathophysiology: we require bone marrow, B12, folate, iron, erythropoietin to produce RBCs with Hb. Haem: Fe2+ + protoporphyrin IX. Globins are haem-containing oxygen binding proteins. B12 and folate and bone marrow needed to make white cells and platelets.
  
• Aetiology of anaemia: deficiency of B12/folate causes megaloblasts in bone marrow and increased MCV. Deficiency of iron causes microcytosis with insufficient Hb (low MCV and MCH concentration). Lack of both causes a dimorphic anaemia with a mixture of small and large RBCs. Reduced bone marrow function: congenital, chemotherapy, infiltration, drugs, parvovirus B19, CKD. Excess blood loss/destruction of red cells, acute or chronic bleeding, chronic or acute haemolysis.

Clinical signs of abnormal FBC

• ↓Hb pale sclerae, hand creases. Fatigue, headache, breathlessness. Symptoms depend on rapidity of onset, cardiorespiratory status, age.
  
• ↓WCC if affected: fever, sore throat, sepsis.
  
• ↓Platelets: petechiae, menorrhagia, epistaxis, haematuria.
  
• Broad assessment of any coexisting illness which can be very varied. Look for fever, large spleen/liver/lymph glands. Look at congenital, racial (thalassaemia/sickle), contacts, travel.
  
• Examine drug chart and recent drugs: phenytoin, cytotoxics, alcohol, quinine.
  
• Investigation: FBC: ↓Hb, WCC, platelets. Haematinics: B12, red cell folate, ferritin/serum iron/TIBC, reticulocytes. U&E: AKI/CKD and CRP. TSH and T4. Bilirubin (red cell breakdown). CXR: infection, malignancy, TB. Blood film: schistocytes, fragmented, deformed, irregular, or helmet-shaped RBCs suggests DIC. Reticulocytes: usually increased except in aplastic anaemia. Bone marrow: hypocellular with aplasia, ringed sideroblasts, megaloblastic. Lack of iron. Infiltration – cancer, infection. Intravascular haemolysis: ↑LDH, reticulocytes, bilirubin, low haptoglobin, Coomb’s test negative. AKI (HUS/TTP or uraemic platelet dysfunction). Upper GI endoscopy with D2 biopsies for coeliac, lower GI endoscopy, capsule endoscopy and CT abdomen for iron deficiency anaemia.
  
• Management: establish cause. Treat and replace. Supportive measures – blood components. Caution with giving Hb in pernicious anaemia with circulatory overload, if future need for bone marrow transplant, check if need irradiated blood (Section 8.17). Take haematology advice if unsure. Bone marrow transplant recipients and patients with cellular immunodeficiency should be considered for CMV negative blood. Focused management on determining cause and replacing components or treating disorder.

• About: thrombocytopenia is platelet count <150 × 109/L. Severe bleeding if count <20–50 × 109/L, worsened by antiplatelets.
  
• Pathophysiology: platelets survive 7–10 days. 35% of all platelets are found in the spleen. Reaction to vessel wall injury is rapid adhesion of platelets to the subendothelium and formation of a haemostatic plug, composed primarily of platelets. This is further stabilised by a fibrin mesh generated in secondary haemostasis. Significant quantitative or qualitative platelet dysfunction results in mucocutaneous bleeding. Platelet count <20 × 109/L can be associated with severe bleeding.
  
• Aetiology: platelets formed from developing megakaryocytes in the bone marrow. Low platelets can be due to a fall in production or increased consumption or sequestration. Platelet dysfunction with antiplatelets, drugs and diseases, e.g. uraemia.

• Clinical: spontaneous petechiae, purpura, bleeding. Mouth may show evidence of bleeding. Check drug chart. Look for splenomegaly and lymph nodes, which may suggest a cause. Menorrhagia, epistaxis, haematuria.
  
• Investigation: FBC: ↓Hb, ↓platelets. If bleeding and platelets >40 × 109/L look for exacerbating cause. U&E: ↑creatinine, check B12, folate, ferritin. Blood film: schistocytes, fragmented, deformed, irregular, or helmet-shaped RBCs suggests DIC. Intravascular haemolysis: ↑LDH, ↑reticulocytes, ↑bilirubin, ↓haptoglobin, Coomb’s test negative. (HUS/TTP or uraemic platelet dysfunction). Coagulation: normal PT, APTT, D-dimer and fibrinogen levels. Increased bleeding time. Renal biopsy if HUS may be indicated to see degree and nature of kidney damage. ADAMTS13 levels of limited use.
  
• Management: treat cause: look for underlying sepsis, drugs, other causes, and treat. Bleeding: direct pressure. If bleeding and ↓count <50 × 109/L then consider IV platelet transfusion and treat cause. Use local physical methods/surgery to stem bleeding. VITAMIN K 5–10 mg IV or orally: if liver disease or VITAMIN K deficiency possible. Avoid NSAIDs, ASPIRIN, and CLOPIDOGREL, warfarin, heparins and DOACs. Augment good mouth care with TRANEXAMIC ACID mouthwashes added if there is bleeding from the oral mucosa. Consider TRANEXAMIC ACID 1 g PO 8 h. Do not give if there is on-going haematuria and/or DIC. Uraemia: consider omitting antiplatelets. Manage uraemia. Pre-eclampsia/eclampsia/HELLP: BP control and fetal delivery.

When to transfuse platelets

• General advice: The use of platelet transfusion to keep the count above 10 × 109/L reduces the risk of haemorrhage as effectively as a higher threshold. May replace to higher levels if patient has taken antiplatelets or has platelet dysfunction or need for surgery or bleeding. Take haematological advice. Must determine cause before transfusion and exclude TTP by examining blood film. Platelets not usually indicated for TTP/HUS/HIT syndromes. In acute ITP only used for real risk of or actual bleeding. The decision to transfuse should be supported by the need to prevent or treat bleeding. There may be a role for desmopressin in patients taking aspirin or uraemia.
  
• Platelets (×109/L) and advice when to transfuse platelets: 0–10: prophylactic transfusion. 10–20: bleeding, fever, infection, platelet dysfunction, coagulopathy. 20–50: prior to minor procedures or in actively anticoagulated patients or in the presence of active bleeding. 50–100: sufficient for most invasive procedures, including gastroscopy and biopsy, insertion of indwelling lines, transbronchial biopsy, liver biopsy, laparotomy, or similar procedures. 50–75: prior to general surgery/childbirth. 50–100: prior to ophthalmic surgery or neurosurgery.

Reference: Lin & Foltz (2005) Proposed guidelines for platelet transfusion. Br Columbia Med J, 47:245.

• About: heparin-induced thrombocytopenia (HIT) + thrombosis (HITT). Heparin induces formation of antibodies with thrombosis and a fall in platelets. Consider HIT in any patient with ↓platelets on heparin started within past 5–10 days.
  
• Types: Type I HIT is a relatively common, non-immune, clinically innocuous and benign reaction. Type II HIT is a rare, immune-mediated, potentially serious form.
  
• Aetiology: formation of platelet-rich thrombosis 5–10 days after starting heparin therapy. Target antigen is a complex between heparin and platelet factor 4 (PF4). More common with UFH, rarer with LMWH. IgG activates platelets via their FcIIa receptors.
  
• Clinical: arterial thrombosis: limb, stroke, MI, PE, renal artery, mesenteric arteries. Skin necrosis at injection sites. Adrenal failure due to vein thrombosis and haemorrhagic necrosis. DVT and HIT can cause venous limb gangrene. Seen day 10 post-UFH.
  
• The 4Ts pre-test probability score: This can assist in determining if HIT is present. Generally, scores of less than 3 suggest the absence of HIT. Higher scores send ELISA for heparin/PF4 antibodies. Not included here for brevity but scoring can be found on www.mdcalc.com.
  
• Investigations: FBC: ↓platelets <150 × 109/L or ↓ by 30–50% after starting heparin therapy (the platelet count may still be normal). U&E: look for AKI. Blood film: fragmented RBCs. Specific test: ELISA for heparin/PF4 antibodies.
  
• Management: stop all heparins (UFH/LMWH/heparin line flushes) in suspected HIT. Urgent haematology advice should be sought. Replace with agents such as the thrombin inhibitor ARGATROBAN. DANAPAROID SODIUM may be used in those with a history of HIT. Also warfarin but needs additional anticoagulation in interim whilst loading as it is a prothrombotic state (protein C levels fall).

• About: seen in 1% of inpatients. Uncontrolled microvascular clotting consumes platelets and clotting factors. Coagulopathy leads to massive haemorrhage, organ failure. Dreadful prognosis. Some say DIC = ‘death is coming’.
  
• Aetiology: endothelial disruption and other initiators lead to a procoagulant state. Formation of microvascular thrombi consumes clotting factors, fibrinogen and platelets. Microthrombi can cause organ dysfunction. Bleeding due to coagulopathy. In malignancy, DIC can be a more chronic process over weeks and months.
  
• Clinical: severe spontaneous bleeding and bruising in an unwell patient. Haemorrhagic shock due to bleeding from lines, GI tract, genitourinary tract, epistaxis. Spontaneous intracerebral haemorrhage, post-operative wound bleed. Bleeding may be hidden, e.g. retroperitoneal, psoas. See also Haemorrhagic shock, Section 2.22.
  
• Causes: trauma and tissue damage, sepsis and septicaemic shock (Gram-negative). Malignancy, acute promyelocytic leukaemia/M3, massive transfusions. Obstetric emergencies (placental abruption, amniotic fluid embolism, eclampsia). Pancreatitis, vascular abnormalities, snake bites, recreational drugs. ABO transfusion incompatibility, transplant rejection, severe liver failure.
  
• Differential: ALF, HUS/TTP, HITT.
  
• Investigations: (*markers of severity) FBC, blood film: anaemia, ↓platelets, fragmented red cells. U&E: AKI, ↑LDH and evidence of haemolysis. Coagulation screen: ↑PT* (>6 s) and ↑APTT, ↑TT, ↓fibrinogen* (<1 g/L), ↓platelets* (50 × 109/L). ↑↑FDPs* due to fibrinolysis (high).
  
• Differential: TTP, HUS, severe hypertension, pregnancy: pre-eclampsia, HELLP syndrome. Microangiopathic haemolytic anaemia.
  
• Management: supportive care: admit ITU. ABC, O2. Care with central lines, coagulopathy. Find and treat the underlying cause. Involve haematology. Clotting factors: give VITAMIN K slow IV 10 mg stat. Replace clotting factors FFP, cryoprecipitate, platelets and red cell concentrates based on bleeding risk more than laboratory results. If there is a prolonged PT and APTT then consider FFP if ↑risk of bleed or procedure or active bleeding. If fibrinogen low (<1 g/L) despite FFP replacement, consider fibrinogen concentrate or cryoprecipitate. Platelets: platelet half-life is short and platelets only given for acute bleeding when less than 50 × 109/L, or the need for a procedure and less than 50 × 109/L. If not bleeding and platelets low, consider transfusing when bleed risk high, e.g. platelets 10–20 × 109/L. Take advice if unsure. Treatment targets: platelets >50 × 109/L, fibrinogen >1 g/L, Hb >80 g/L, PT and APTT <1.5× normal. IV HEPARIN: may rarely be used to reduce the clotting. Indications include arterial or venous thromboembolism, severe purpura fulminans with acral ischaemia or vascular skin infarction. It should possibly not be stopped if patient already on it. Avoid IV TRANEXAMIC ACID except where there is severe bleeding and a hyperfibrinolytic state. One can augment mouth care with oral TRANEXAMIC ACID solution as a mouthwash which can help reduce oozing from friable oral mucosa.

Reference: British Committee for Standards in Haematology (2009) Guidelines for the diagnosis and management of DIC. Br J Haematol, 145:24.

• About: chronic haemolytic anaemia. Abnormal Hb first described by Linus Pauling in 1946. Commoner in black patients but may also affect other groups. Homozygous inheritance of HbSS or HbSC. Most painful crises are managed at home.
  
• Aetiology: HbSS contains 2 defective β-globin chains due to a Valine to Glutamate substitution on the β6 position. Structural change and HbS polymerisation and sickling at low O2 tensions. HbAS: symptoms with extreme hypoxia (sickle cell trait).
  
• Acute crises seen with HbSS:
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