Sickle Cell Disease (Haemoglobin SS)
This is an inherited disease of the haemoglobin, which resides within red blood cells; it carries oxygen to tissues. In this condition, owing to a genetic defect, the deformability of the red cell around the fine capillaries of the body is limited, and they may be aggregated and block vessels. It is inherited in a way that if only one of the genes is affected (HbS), this is called trait and these features are much less likely to occur than if both genes are affected (HbSS).
The blocking of vessels leads to the following complications:
Sequestration of red blood cells (simply means huge collections) with organs such as the liver, spleen, lungs, muscle and even in organs such as the penis given rising to painful priapism.
The affected areas have insufficient oxygen levels and ischaemia and subsequent cell death can occur. This may give rise to ‘painful crises’.
These conditions can be very difficult to manage and may require exchange transfusion, a process of painstakingly removing small aliquots of blood and replacing this volume with fresh blood. This decreases the percentage of sickled red blood cells and improves the oxygen carrying capacity of the blood.
Small vessel disease can affect other organs such as the spleen who function is to remove bacteria such a pneumococcus and Haemophilius influenza. This means that these patients are at risk of overwhelming sepsis – in the untreated population, mortality rates of 10% are reported in under 2 year olds. Preventative immunization agents are used as is prophylactic antibiotics to prevent the development of sepsis and septic shock. Other implicated bacterial infecting agents include: Staphylococcus aureus, Klebsiella and Salmonella.
Other sites of infection include the bone (osteomyelitis) and even sepsis of the joints (septic arthritis).
Neurological signs may be found in the event of a ‘stroke’ occurring. This may be due to blockage of small vessels as described above. This has a significant mortality rate as does a ‘chest syndrome’. In this latter condition, the blockage of capillaries leads to localised decrease of oxygen levels which in turn causes vasoconstriction, i.e. the blood vessels become small and so worsens the local oxygen concentrations fall even further. A domino effect may be observed and generalized hypoxia with subsequent death without treatment (even with treatment, there is a significant risk of death).
There is susceptibility to infection with parvovirus B19 that cause an aplastic crisis, i.e. when there is a failure of production of cells from the bone marrow.
Rare complications include gallstones, failure of growth in bones who growth plates have been stunted owing to localized ischaemic events.
This is a lifelong condition requiring daily ingestion of prophylactic antibiotics and immunisations to prevent infection with potentially lethal bacterial infections. Bone marrow transplantation is successfully used as a treatment, but is not universally available.
There are helpful support groups, including the Sickle Cell Society http://www.sicklecellsociety.org
NICE has also produced healthful clinical guidance on the management of the following elements of sickle cell care.
Scenario: Screening : Provides information on the national screening programme to detect sickle cell disease and other disorders, such as sickle cell trait and thalassemia.
Scenario: Management - sickle cell crisis : Covers the management of a sickle cell crisis in primary care.
Scenario: Management - chronic complications : Covers the management of chronic complications of sickle cell disease in primary care.
Scenario: Prevention of complications : Covers the prevention of complications of sickle cell disease, including the use of immunizations, prophylactic antibiotics, and folic acid supplements in primary care.
Scenario: Management - sickle cell trait : Covers the management of sickle cell trait in primary care.
Scenario: Contraception : Covers recommendations for the use of contraception in women with sickle cell.