Changes

==Diagnosis==

==Diagnosis==

Diagnosis may not be straightforward as the clinical signs may resemble those of many other infections occurring in foals. The antemortem diagnosis of SCID is usually based on three criteria; a) a persistent lymphopaenia (occurring over 1-2 weeks) with less than 1000 lymphocytes per ml, b) a lack of serum IgM in foals over four weeks of age and c) lymphoid hypoplasia. Affected foals may also develop [[Anaemia - Introduction|anaemia]] late in the course of the disease.  

Diagnosis may not be straightforward as the clinical signs may resemble those of many other infections occurring in foals. The antemortem diagnosis of SCID is usually based on three criteria; a) a persistent lymphopaenia (occurring over 1-2 weeks) with less than 1000 lymphocytes per ml, b) a lack of serum IgM in foals over four weeks of age and c) lymphoid hypoplasia. Affected foals may also develop [[Regenerative and Non-Regenerative Anaemias|anaemia]] late in the course of the disease.  

The '''intradermal phytohemagglutinin (PHA) test''' may be used as a test for immunocompetence and assesses T lymphocyte function. It can be performed in foals of all ages as the test is not affected by maternal antibodies. Intradermal PHA causes a [[Type IV Hypersensitivity|delayed hypersensitivity]] reaction, resulting in a skin swelling. A foal suffering from SCID fails to respond to intradermal PHA.  

The '''intradermal phytohemagglutinin (PHA) test''' may be used as a test for immunocompetence and assesses T lymphocyte function. It can be performed in foals of all ages as the test is not affected by maternal antibodies. Intradermal PHA causes a [[Type IV Hypersensitivity|delayed hypersensitivity]] reaction, resulting in a skin swelling. A foal suffering from SCID fails to respond to intradermal PHA.