Sickle Cell Anaemia Case Study Biology Essay

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Daniel Degreiss, a 17-year old Afro-Caribbean male, arrived in A & E very short of breath. He has sickle-cell disease, and has been in and out of hospital with crises all his life. His mother reported that he had become increasingly ill over the past week. Initially she thought he had a cold; then he began to complain of a pain in the right side of his chest that hurt him when he breathed and when he coughed. He had argued with his mother for two or three days previously because he had not wanted to come into the hospital.

On examination: looks ill, with central cyanosis; respiration rate 35/minute; heart rate 130/minute; body temperature 39.6oC.

On examination: haemoglobin concentration 8.9g/100ml; blood film showed sickle-shaped erythrocytes; white blood cell count 25,000/cu. mm. (95% neutrophils). Purulent sputum contained many neutrophils and Gram-positive diplococci; a blood culture grew the same micro-organism.

The A & E doctors and their haematology colleagues diagnose pneumonia and septicaemia, with Streptococcus pneumoniae identified as the cause. He is treated initially with intravenous cephalosporin, but penicillin G is substituted when the bacterial sensitivities are known.

His mother has had to take a lot of time off work in the past, and Daniel has missed a lot of school. Although he had had a good relationship with the treatment team in recent years, since he has been a teenager he has been increasingly surly and independent, and doesn't want to listen to advice.


Sickle Cell Disease & Crises, Pneumonia, Septicaemia, Central Cyanosis, Gram Positive, Blood Cultures, Streptococcus Pneumoniae, Purulent Sputum, (IV, IM, SC, IP), Erythrocytes, Neutrophils,


What does Cephalosporin & Penicillin do?

Explain pain in right chest

What is a normal respiration rate, heart / pulse rate & body temperature?

Discover normal haemoglobin levels / white blood cell count

What are bacterial/antibiotic sensitivities?

Discuss the psychosocial aspects

Why are Sickle Cell sufferers more susceptible to streptococcal infections?

Fig 1 - Sickle Cell SummarySickle Cell Disease

On the gene that codes for the β-globin chain, @ the 17th nucleotide (position 6), a missense mutation causes the nucleotide base Adenine to be substituted by Thymine. The codon GAG, which codes for glutamic acid, becomes GTG, coding for valine.

Sickle cell haemoglobin (HbS) is now produced instead of the normal adult haemoglobin (HbA); while HbA2 and HbF (foetal haemoglobin) are still produced. The disease itself is an autosomal recessive genetic disorder, thus the gene must be inherited from both parents - resulting in HbSS (homozygote form), to manifest. Otherwise a carrier of HbS is known genotypically as HbAS (heterozygote for) and carries "sickle cell trait". (See figure 2)

HbS is present in 15% of the black population, mainly affecting those of African descent, as well as those from South American and South Asian areas. (See figure 3)

Fig 3 - risk relative to location

Fig 2 - Mode of Inheritance

♦ High Risk

♦ Medium Risk

♦ Low Risk

♦ Very Low Risk

♦ No Risk

♦ High Risk

♦ Medium Risk

♦ Low Risk

♦ Very Low Risk

♦ No Risk chart that shows the probabilities of children inheriting sickle cell traits from their parents.

HbS polymerises when deoxygenated, the proteins in the erythrocytes form rigid rods, changing the cell shape to one resembling a sickle - hence sickle cell. These become inflexible and difficult to flow, as well as being more easily phagocytosed.

They also become more adherent to vascular endothelium. Sickling is initially reversible but red cells become progressively more rigid due to membrane defects. Sickled red cells have reduced lifespan and result in chronic haemolysis. [1]

This leads to microvascular occlusions - obstructions of vessels such as capillaries, and sickle cell crises, which increases ones risk of stroke and mesenteric ischaemia.

These occlusions are first noticeable as acute pain in the hands and feet (dactylitis) in the first few years of life. Severe pain in other bones e.g. femur, humerus, vertebrae, ribs, pelvis, occurs in older children/adults. These attacks vary in frequency from daily to perhaps once a year. Fever often accompanies the pain. [2]

A splenic infarction / sequestration occurs when the blood flow to the spleen is inhibited, thus reducing its oxygen supply. This is one of the first infarctions a sufferer may have, often before 24months. The spleen is painfully enlarged and pooling of red blood cells and hypovolaemia may occur, leading to a fibrotic, non functioning spleen. [2]

This increases one's susceptibility to infection, due to a reduced clearance of encapsulated bacteria from the bloodstream. [3]

Diagnostic Tests:

Blood Count: Hb level 6-8g/dL with a high reticulocyte count (10-20%)

Blood Films (microscopic investigation of a drop of blood): can show features of hyposplenism and sickling.

Sickle Solubility Test: test for presence of HbS, when added to a reducing solution of sodium dithionite, solution becomes turbid, otherwise clear with HbA

Hb Electrophoresis is required to confirm a diagnosis, as the sickle solubility test (above) does not distinguish between HbAS and HbSS. A positive result shows no HbA, 80-95% HbS and 2-20% HbF. [2]

Fig 4. Hb Electrophoresis

Long Term Problems:

Lower weight

Delayed sexual maturation

Acute chest syndrome in up to 30% due to infection

Pulmonary hypertension and chronic lung disease are the most common cause of death for those with sickle cell anaemia



Exchange transfusions are given to maintain HbS levels at below 20%

Analgesia such as morphine



Vaccinations for potential infections like influenza

An IV saline drip can be used to keep blood pH >7, decreasing the likelihood of sickling

Hyrdroxyurea when given stimulates production of HbF, which lowers the proportion of abnormal HbS.



Pneumonia is an acute lower respiratory tract illness associated with fever, symptoms and signs in the chest and abnormalities on the chest x-ray. Incidence of community acquired pneumonia is 12 per 1000 adults, and the most common cause of this (60-75%) is by streptococcus pneumoniae.

Symptoms: Fever, rigors, malaise, anorexia, dyspnoea, cough, purulent sputum, haemoptysis and pleuritic pain.

Signs: Fever, cyanosis, confusion (may be the only sign in the elderly), tachypnoea, tachycardia, hypotension.

Diagnostic Tests: Blood cultures, Sputum Cultures, Pleural fluid culture, X-ray, Arterial Blood Gas if O2 sat <92%, full blood count



Bacterial pneumonia

Treatment for pneumonia should ideally be based on the causative microorganism and its known antibiotic sensitivity. Amoxicillin and clarithromycin or erythromycin are the antibiotics selected for most patients with community-acquired pneumonia; patients allergic to penicillins are given erythromycin instead of amoxicillin. Antibiotics for hospital-acquired pneumonia include third- and fourth-generation cephalosporins among others.

Viral pneumonia

Viral pneumonia caused by influenza A may be treated with rimantadine or amantadine, while viral pneumonia caused by influenza A or B may be treated with oseltamivir or zanamivir. These treatments are beneficial only if they are started within 48 hours of the onset of symptoms.


[3] Flow chart of pneumonia management


Widespread destruction of tissues due to absorption of disease causing bacteria or their toxins from the blood stream. The term is also used loosely for any form of blood poisoning. Sufferers will require a hospital stay. [7]

Central Cyanosis:

Cyanosis is the bluish discoloration of the skin and mucous membranes, when the capillary oxygen saturation is less than 85%. Central cyanosis is seen with the shunting of deoxygenated venous blood into the systemic circulation, as in the presence of a right-to-left heart shunt. [8]

Central cyanosis occurs when there is more than 50g/L of deoxyhaemoglobin present. It is seen in the buccal mucosa, lips and tongue and may indicate hypoxia. In anaemia when haemoglobin levels are low, cyanosis levels may not be apparent even if the patient is hypoxic. [9]

Central cyanosis is often due to a circulatory or ventilatory problem that leads to poor blood oxygenation in the lungs or greater oxygen extraction due to slowing down of blood circulation in the skin's blood vessels. [10]

Gram Positive:

Gram-positive bacteria are those that are stained dark blue or violet by Gram staining. Gram-negative bacteria cannot retain the crystal violet stain, instead taking up the counterstain and appearing red or pink. Gram-positive organisms are able to retain the crystal violet stain because of the high amount of peptidoglycan in the cell wall. Gram-positive cell walls typically lack the outer membrane found in Gram-negative bacteria. [12]

Gram-positive includes many well-known genera such as Staphylococcus, Streptococcus, Enterococcus, (which are cocci) and Bacillus, Clostridium, and Listeria. [12]

[1] Diagram comparing gram positive and gram negative bacteria

Blood Cultures:

Blood cultures are used to detect the presence of bacteria or yeasts in the blood, to identify the microorganism(s) present, and to guide treatment.

Streptococcus Pneumoniae:

Streptococcus pneumoniae cells are Gram-positive, (aerobic), lancet-shaped cocci. Usually, they are seen as pairs of cocci (diplococci), but they may also occur singly and in short chains. When cultured on blood agar, they are alpha hemolytic. Individual cells are between 0.5 and 1.25 micrometers in diameter. [14]

Purulent Sputum:

Sputum: The mucus and other matter brought up from the lungs, bronchi, and trachea that one may cough up and spit out or swallow. The word "sputum" is borrowed directly from the Latin "to spit." [15]

Purulent simply means "pus containing". Pus is a thick white or yellowish fluid that is constituted of decomposed body tissue, bacteria (or other micro-organisms that cause the infection), and dead phagocytes.

An accumulation of pus in an enclosed tissue space is known as an abscess, while a visible collection of pus within or beneath the epidermis is known as a pustule or pimple. Pus is produced from the dead and living cells which travel into the intercellular spaces around the affected cells. [17]

(IV, IM, SC, IP):

IV: Intravenous

IM: Intramuscular

SC: Subcutaneous

IP: Interphalangeal



(Technical name for a red blood cell). A blood cell containing the red pigment haemoglobin, the principal function of which is the transport of oxygen. A mature erythrocyte has no nucleus and its shape is that of a biconcave disc approximately 7µm in diameter. There are normally about 5 x 1012 erythrocytes per litre of blood. [19]


Are a polymorph and variety of granulocyte / white blood cell. They have a lobed nucleus and their cytoplasm has granules that stain purple with Romanowsky stains. They phagocytose and kill bacteria by releasing hydrolytic enzymes from their granules. [20]

What does Cephalosporin & Penicillin do?

Both penicillin and cephalosporin are beta-lactam antibiotics.

Penicillin G is also known as benzylpenicillin, "gold standard" penicillin, derived from the penicillium fungus. It is administered by a parenteral / non-oral route such as an injection / IV.

Cephalosporin, from cephalosporium, is a semi-synthetic, broad spectrum antibiotic.

When combined, these two drugs may display "cross sensitivity", whereby the patient has an allergic reaction, namely irritation in the GI tract.

Beta-lactams disrupt the synthesis of the cross links in the peptidoglycan cell wall, by affecting the enzyme DD-transpeptidase - thus as this weakened form expands, it is destroyed by osmotic lysis.

What is a normal respiration rate, heart / pulse rate & body temperature?

A rectal or ear (tympanic membrane) reading is 0.5 to 1°F (0.3 to 0.6°C) higher than an oral reading. A temperature taken in the armpit is 0.5 to 1°F (0.3 to 0.6°C) lower than an oral reading.

Body temperature


Average: 98.6°F (37°C).


Oral: 100°F (37.8°C) Tympanic: 101°F (38.3°C) indicates a slight fever.

Rectal: 100.4°F (38°C) or higher in a child indicates a fever.

Tympanic less than 97°F (36.1°C) indicates hypothermia.


Average respiratory rates, by age, in breaths per minute.

Newborns: Average 44

Infants: 20-40

Older children: 16-25

Adults: 12-20

Adults during strenuous exercise 35-45


A normal heart rate for an adult at rest is 60-80 BPM. Bradycardia occurs when the pulse rate is below 60 per minute but is only usually symptomatic when below 50BPM, whereas tachycardia occurs when the rate is above 100 BPM. During sleep, the pulse can drop to as low as 40 BPM; during strenuous exercise, it can rise as high as 150-200 BPM.


Discover normal haemoglobin levels / white blood cell count

Haemoglobin Test:

Normal values in an adult are 12 to 18 grams per decilitre of blood. Above-normal haemoglobin levels may be the result of:


excess production of red blood cells

severe lung disease

Below-normal haemoglobin levels may lead to anemia that can be the result of:

iron deficiency or other deficiencies, such as B12 and folate,

inherited haemoglobin defects, such as sickle cell anaemia or thalassaemias,

excessive bleeding,

excessive destruction of red blood cells,


White blood cell count:

Normal values for total WBC and differential in adult males and females are:

Total WBC: 4,500 - 10,000 ( white blood cells per microlitre )

Bands or stabs: 3 - 5 %

Granulocytes (or polymorphonuclears)

Neutrophils (or segs): 50 - 70% relative value (2500-7000 absolute value)

Eosinophils: 1 - 3% relative value (100-300 absolute value)

Basophils: 0.4% - 1% relative value (40-100 absolute value)

Agranulocytes (or mononuclears)

Lymphocytes: 25 - 35% relative value (1700-3500 absolute value)

Moncytes: 4 - 6% relative value (200-600 absolute value)

Each differential always adds up to 100%.


What are bacterial/antibiotic sensitivities?

Antibiotic sensitivity is a term used to describe the susceptibility of bacteria to antibiotics. Antibiotic susceptibility testing (AST) is usually carried out to determine which antibiotic will be most successful in treating a bacterial infection in vivo. Testing for antibiotic sensitivity is often done by the Kirby-Bauer method. [26]

Discuss the psychosocial aspects

Daniel may suffer racial discrimination at school for having a "black disease". He may be singled out and stigmatised for being of weaker health and inferior physically and be a target of bullying. Others may believe what he has is contagious and will stay away from him, harming his social value. This can affect his mental state, feeling left out and in need of greater parental support. His school work and attendance may be compromised. Due to delayed sexual maturation and a potentially shorter stature it is possible Daniel feels different to the other boys in the group and is disadvantaged in any relationships he tries to forge. Hormonal imbalances at this age may induce irrational thoughts of depression or increase the likelihood of domestic arguments with his family.

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