Emergency department haematology

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Chapter 43 Emergency department haematology

Anthony J. Dodds

COMMON HAEMATOLOGICAL EMERGENCIES

Neutropenic sepsis

(Also see Chapter 42, ‘The immunocompromised patient’.)

Severe neutropenia is defined as a neutrophil count less than 0.5 × 10⁹/L, but severe sepsis is unusual until the neutrophil count is less than 0.2 × 10⁹/L. Causes for severe neutropenia include cancer chemotherapy drugs, agranulocytosis (an idiosyncratic reaction to an otherwise non-marrow suppressive drug) and haematological disorders causing marrow failure (acute and chronic leukaemias, myeloma, lymphoma, aplastic anaemia etc).

Patients presenting with a fever above 38°C require urgent investigation and therapy.

Investigations

Investigations should be directed to possible sites of infection; however, local sites are detected in fewer than 50% of such patients. Suggested investigations include chest X-ray, blood cultures and urine culture. If there is a central line, cultures through this line are also important.

Management

Therapy with broad spectrum antibiotics should not be withheld while investigations are being performed. Gram negative infections usually arising from the gut are the commonest causes but, in the presence of a central venous catheter, treatment of possible gram positive skin organisms should also be considered.

Most institutions have an approved protocol to treat such patients. Usually a broad spectrum cephalosporin is combined with gentamicin until Pseudomonas has been excluded. If the fever does not respond to this after 48 hours or a central venous catheter is present, then additional antistaphylococcal therapy is added.

Severe thrombocytopenia and bleeding

Severe bleeding with thrombocytopenia is not usually a problem until the platelet count is less than 10 × 10⁹/L. When patients present with bleeding secondary to thrombocytopenia, an urgent assessment of the cause of the thrombocytopenia is necessary.

Differential diagnosis

1. Marrow failure, e.g. chemotherapy drugs, haematological malignancy etc. Such patients usually have a pancytopenia and a history of being given marrow suppressive therapy. Urgent platelet transfusion is indicated.

2. Peripheral destruction of platelets. This may be an autoimmune disorder (immune thrombocytopenic purpura or ITP) or less commonly an immune drug-related disorder. Heparin is a common drug cause for immune thrombocytopenia. Patients presenting with ITP may have no preceding history and have isolated thrombocytopenia. The disorder may be postviral and reversible in children but commonly chronic in adults. If there is any doubt about the diagnosis, a marrow biopsy is indicated. This will show a normal marrow with plentiful megakaryocytes. Urgent corticosteroids (prednisolone 1 mg/kg daily) are indicated for ITP with severe thrombocytopenia, especially with bleeding.

3. Disseminated intravascular coagulation (DIC). DIC can occur with malignancy or severe sepsis. Treatment is aimed at the underlying cause rather than treating by platelet transfusion alone.

THE ANAEMIC PATIENT

Anaemia is defined as a reduced haemoglobin (Hb) concentration in the blood. The red cell mass and the plasma volume can affect this value, so both these factors must be considered when interpreting a single value. Thus, severe dehydration can produce an elevated Hb and increased plasma volume, such as in pregnancy, can produce a falsely low Hb.

The symptoms and signs of anaemia (pallor, fainting, lethargy and anorexia) are unreliable. Anaemia may be asymptomatic and detected only on a routine blood count. The cause of anaemia can be ascertained by a logical sequence of investigations as follows. This is based on the mean corpuscular volume (MCV), which is part of an automated blood count.

Microcytic (normal MCV)

• Iron deficiency—serum ferritin low

• Thalassaemia trait—serum ferritin normal or raised

Macrocytic (raised MCV)

• Megaloblastosis—low serum B₁₂ or red cell folate levels

• Secondary macrocytic anaemia, e.g. alcohol, liver disease, hypothyroidism, some marrow disorders, marked reticulocytosis

Principles of therapy

1. Establish the cause and treat.

2. Blood transfusion only indicated for:

• acute anaemia with hypovolaemia

• refractory anaemias (Hb < 80 g/L)

• severe symptoms, e.g. angina.

3. Most patients with anaemia do not need blood transfusion unless the Hb < 80 g/L. Transfusion can be risky with severe compensated anaemia, especially in the elderly and those with cardiac disease.

THE PATIENT WITH ABNORMAL BLEEDING

Screening haemostasis tests are not warranted or cost effective in the absence of clinical signs or history to suggest a bleeding diathesis.

The following are suggestive:

• family history of bleeding disorder

• past history of excessive bleeding with minor haemostatic insults, e.g. tooth extraction, minor surgery, minor trauma, childbirth

• excessive local bleeding without an obvious cause

• generalised bleeding or bruising.

The usual screening tests are:

• vascular or platelet disorder—platelet count (PC), platelet function tests

• coagulation disorder—prothrombin time (PT), activated partial thromboplastin time (APTT), thrombin time (TT).

The following is a guide to the interpretation of these tests.

Platelet and vascular defects

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