D55.9 – Anaemia due to Enzyme Disorder | ICD-10
D55.9 is an ICD-10 diagnosis code for anaemia due to an enzyme disorder, unspecified. It refers to a rare, usually hereditary form of haemolytic anaemia.
Things worth knowing about "D55.9"
D55.9 is an ICD-10 diagnosis code for anaemia due to an enzyme disorder, unspecified. It refers to a rare, usually hereditary form of haemolytic anaemia.
What is D55.9?
D55.9 is an ICD-10 diagnosis code representing anaemia due to enzyme disorder, unspecified. This code is applied when anaemia is caused by a deficiency or malfunction of a red blood cell enzyme, but the specific enzyme defect has not been further identified. Enzyme-related anaemias belong to the group of haemolytic anaemias, in which red blood cells (erythrocytes) are broken down prematurely.
Causes
Anaemias due to enzyme defects arise from genetically determined disorders in the metabolism of red blood cells. The most common causes include:
- Glucose-6-phosphate dehydrogenase (G6PD) deficiency: The most common red blood cell enzyme defect worldwide, which can be triggered by certain medications, infections, or foods (e.g. fava beans).
- Pyruvate kinase deficiency: A rare, autosomal recessive inherited defect that leads to chronic haemolytic destruction of erythrocytes.
- Other enzyme defects: Rare defects of other enzymes in the glycolytic pathway or the pentose phosphate pathway may also be responsible, and are classified under D55.9 when no further specification is possible.
Symptoms
Clinical signs can vary depending on the type and severity of the enzyme defect. Typical symptoms include:
- Fatigue, weakness, and general malaise
- Pale skin and mucous membranes
- Jaundice (icterus) due to increased bilirubin breakdown
- Enlarged spleen (splenomegaly)
- Dark urine (haemoglobinuria), especially during haemolytic crises
- Shortness of breath during physical activity
- In severe cases: haemolytic crises with a rapid drop in haemoglobin levels
Diagnosis
The diagnosis of enzyme-related anaemia is established through a combination of:
- Complete blood count: Detection of anaemia (reduced haemoglobin and haematocrit values)
- Blood smear: Characteristic changes in red blood cells (e.g. Heinz bodies in G6PD deficiency)
- Reticulocyte count: Elevated reticulocytes as a sign of increased red cell turnover
- Enzyme activity assays: Specific tests to measure the activity of suspected enzymes
- Genetic testing: To confirm the diagnosis and provide counselling for family members
Treatment
Treatment depends on the underlying cause and severity of the anaemia:
- Avoidance of triggers: In G6PD deficiency, certain medications (e.g. primaquine, dapsone), fava beans, and infections should be avoided.
- Folic acid supplementation: To support increased red blood cell production.
- Blood transfusions: Required during severe haemolytic crises or in cases of profound anaemia.
- Splenectomy: In selected cases (e.g. severe pyruvate kinase deficiency), surgical removal of the spleen can reduce haemolysis.
- Novel therapies: For pyruvate kinase deficiency, mitapivat was approved in 2022 as an enzyme activator to reduce haemolysis.
References
- World Health Organization (WHO): ICD-10 Classification of Mental and Behavioural Disorders, Volume 1. Geneva: WHO; 2019. Code D55.9 – Anaemia due to enzyme disorder, unspecified.
- Zanella A, Bianchi P. Red cell pyruvate kinase deficiency: from genetics to clinical manifestations. Best Practice & Research Clinical Haematology. 2000;13(1):57–81.
- Frank JE. Diagnosis and management of G6PD deficiency. American Family Physician. 2005;72(7):1277–1282.
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