Introduction: Human combined immunodeficiency (CID) was first reported more than 50 years ago. It is now known that CID can be caused in humans by mutations of many different genes and the likelihood is that there are other causes yet to be discovered. Regardless of the underlying defect infants with this syndrome are lymphopenic and have profound deficiencies of T and B cell numbers and function. Recognition of the characteristic lymphopenia can result in early diagnosiseven at birth. Flow cytometric studies have shown that there are unique lymphocyte phenotypes for the various genetic forms of CID.

Materials and Methods: Fourteen-four patients who fulfill the criteria of CID, flow cytometric analysis were performed by using Beckman Coulter, Epics XL -MCL; System II software; Miami, Florida, USA. Monoclonal antibodies, anti-CD3, anti- CD4, anti-CD8, anti-CD16, anti-CD56 and anti-CD19 were also purchased from Beckman Coulter. Absolute lymphocyte numbers of patient and control groups were compared statistically.Results and

Discussion: Affected infants all presented with common problems such as oral moniliasis, diarrheas, severe pneumonias and failure to thrive in the first few months of life. Our CID group which is amongst the largest groups presented from Turkey, showed the clinical features necessary to suspect from this rare syndrome and the distribution of the CID phenotypes in Turkey. The 44 CID patients seen in 7 years, 95% showed ALC<3000/mm while only one patient of the control group with the similar infections had ALS<3000/mm . This study demonstrated the potential of ALC to diagnose CID routinely under 1 year of age showing severe infections. We suggest that if the ALC of <3000/mm is seen, efforts should be made for the early diagnosis of CID

Keywords: Combined Immunodeficiency