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3.2: Sickle Cell Disease (SCD)

Table of Contents

Sickle Cell Disease describes a group of inherited red blood cell disorders characterized by the presence of hemoglobin S or sickle hemoglobin. Sickle cell anemia (SCA), is when an individual inherits two copies of hemoglobin S (homozygous state, HbSS).

Clinical Features:

The clinical manifestations of SCA are variable; acute onset of unexplained illness, including acute pain in any part of the body, anaemia, acute neurological symptoms, and loss of vision, collapse, respiratory symptoms, hepatosplenomegaly, jaundice, swollen limbs and sepsis should be tested for SCD. Symptoms usually occur after 6 months of life and may fall into any of the four types of crisis that occur in SCD

  • Vaso-occlusive crisis: painful crisis usually presenting as back pain, pain in the upper/lower limbs, joint pain, abdominal pain, chest pain. It is important that other causes of pain are ruled out.
  • Hemolytic crisis: presents with features of anemia, jaundice, may have dark urine signifying intravascular hemolysis
  • Sequestration crisis: sudden massive enlargement of the liver and spleen accompanied with a fall in hematocrit
  • Aplastic Crisis: Where the bone marrow ceases to function – reflected by a worsening of anemia in the absence of reticulocytosis.

Medical Emergencies:

The following are life threatening complications that may lead to rapid deterioration and death if not diagnosed and managed in a timely manner

  1. Acute Chest Syndrome – Presents with chest pain, tachypnoea, respiratory distress, fever, decreased oxygen saturation and chest X-Ray infiltrates
  2. Splenic sequestration – Usually occurs in children, characterised by splenic enlargement, left upper quadrant pain, pallor, weakness, rapidly falling hemoglobin levels and hypovolaemia
  3. Infection – Most individuals with SCD develop functional asplenia (due to recurrent splenic infarction) by the age of five, and are therefore immuno compromised.
  4. Stroke – May present with headache and neurological deficit.

Investigations:

Screening Tests for SCD include

  • Sickling Test
  • Sickle Solubility Test

Confirmatory Tests for SCD include:

  • Sickle Scan
  • Iso Electric Focusing (IEF)
  • Haemoglobin elecrophoresis
  • HPLC (High Pressure Liquid Chromatography)

Other ancillary laboratory investigations useful in detection and monitoring of the disease include:

  • FBC – Red cell indices may suggest macrocytosis due to increased reticulocytosis or compliance with hydroxyurea therapy
  • Reticulocyte count – usually ranges from 5–15% in sickle cell disease
  • Peripheral blood film – findings may include irreversible sickled red cells, polychromasia, occasional nucleated red cells, and schistocytes, as well as Howell-Jolly bodies. Target cells may also be seen.
  • Biochemical changes include high LDH, low haptoglobin, high total and indirect bilirubin, and high AST.

Pharmacological Management

Prophylaxis Against Pneumococcal Infection

Administer prophylactic

A: Phenoxymethyl penicillin (125 mg PO for children younger than 3 years; 250 mg PO for children 3 years and older) twice daily until 5 years of age in all children with SCA

Immunisation against pneumococcal infection

A: Pneumococcal conjugate vaccine (PCV-13) – from two months of age, 3 doses 8 weeks apart (i.e at age 2months, 4 months and 6 months) and a booster dose between 12–15 months. If the child has not previously received this vaccine, then at least one dose should be given between 6–18 years.

A: Pneumococcal polysaccharide vaccine (PPSV-23) – at 2 years then after every 5 years for life.

Screening

o From the age of 10 years, screen for renal disease (proteinuria by urine dipstick) and retinopathy annually
o Annual screening for risk of stroke by transcranial Doppler from the age of 2 years to 16 years.

Table 3.1: Analgesia for General Pain Relief

Severity Management
Mild Reassurance, hot packs, reposition, massage, distraction (stories, play)

Child: Paracetamol 15mg/kg (PO) 6 hourly

Adult: Paracetamol 1g (PO) 6 hourly

Moderate As for mild pain, PLUS

Child: Ibuprofen 5mg/kg (PO) 8 hourly

Adult: Ibuprofen 400mg (PO) 8 hourly

Severe As for moderate pain PLUS

Child: Oral morphine 0.5mg/kg 3–4 hourly as needed

Adult: Oral morphine 5–10mg, 3–4 hourly as needed


Hydration
: Encourage oral fluids first; it should be used whenever possible. Give IV fluids if the patient is unable to drink well, has severe pain, abdominal symptoms, or is not settling

Body weight (kg) Fluids (ml/kg/day)
<10 kg 150ml/kg/day
11 – 20kg 75ml/kg/day for every kilogram above 10kg

ADDED to 1500ml for the first 10kg of weight

> 20kg 30ml/kg for every kilogram above 20kg

ADDED to 225Oml for the first 20kg of weight

Divide the total daily volume by 24 hours to obtain hourly fluid rate


S: Hydroxyurea Therapy

Hydroxyurea is currently the only approved disease modifying drug for use in selected patients with SCD over the age of 24 months

Indications for use of Hydroxyurea Include:

  1. Recurrent VOC ( 3 or more severe episodes requiring admission in the last 12 months)
  2. Severe and/or recurrent ACS (2 or more episodes in a lifetime)
  3. Severe symptomatic chronic anemia that interferes with daily activities or quality of life
  4. Where chronic transfusion therapy is not feasible it can be used as an alternative to prevent new or recurrent stroke.
  5. Recurrent priapism
  6. In adults and children with SCD who have chronic kidney disease and are taking erythropoietin, hydroxyurea therapy can be added to improve anemia

Principle of Dosage Initiation and Monitoring:

  1. Starting dosage for adults (500 mg capsules): 15 mg/kg/day (PO) (round up to the nearest 500 mg); 5–10 mg/kg/day (PO) if patient has chronic kidney disease
  2. Starting dosage for infants and children: 20 mg/kg/day
  3. Full blood counts are monitored weekly for the first 4 weeks, fortnightly for the next 8 weeks, and thereafter monthly if the counts remain stable
  4. Increase the dose by 2.5–5 mg/kg/day every 12 weeks (range of 4 weeks to 6 months) if absolute neutrophil count (ANC) >2000/µL, Haemoglobin concentration >4.5 g/dL, and platelet count >80,000/μL
  5. If neutropenia or thrombocytopenia occurs:
    • Hold hydroxyurea dosing
    • Monitor CBC with WBC differential weekly
    • When blood counts have recovered, reinstitute hydroxyurea at a dose 2.5 mg/kg/day less than the dose given before onset of cytopenias to achieve the maximum tolerable dose
  6. Once a stable dose is established, laboratory safety monitoring should include a FBC and reticulocyte count every 2–3 months
NOTE:
 

 

Hydroxyurea should be discontinued in all pregnant women
Hydroxyurea should be discontinued in all breast feeding women
Hydroxyurea should be stopped at least three months prior to conception in both males and females

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