Short Answer 
The diagnosis process for Lucy involved three key steps: ruling out HIV, checking Deoxyadenosine levels in her blood, and confirming an ADA-SCID diagnosis based on elevated Deoxyadenosine levels. This sequence was crucial for identifying her condition and determining appropriate treatment options.
Step 1: Rule Out HIV
The initial step in diagnosing Lucy was to ensure she did not have HIV. This was crucial, as the presence of HIV proteins in her blood would have indicated a different condition. Thus, testing her blood for the specific proteins was necessary to effectively eliminate the possibility of an HIV infection.
Step 2: Identify Deoxyadenosine Levels
Once HIV was ruled out, the next step involved checking the levels of Deoxyadenosine in Lucy’s blood. High quantities of this substance can indicate a metabolic issue related to the immune system. It is essential to carry out this test to gather evidence of any potential disorders affecting her health.
Step 3: Confirm ADA-SCID Diagnosis
After establishing that Lucy had elevated Deoxyadenosine levels, it pointed towards a diagnosis of ADA-SCID (Adenosine Deaminase Deficiency- Severe Combined Immunodeficiency). This condition occurs when the enzyme responsible for converting Deoxyadenosine into a different molecule is not functioning properly, leading to excess Deoxyadenosine in the bloodstream. Confirming this diagnosis allows for specific treatment options to be considered.