The Diagnostic Path: Tests and Reports

Diagnosing an ultra-rare condition like CD70 deficiency is a multi-step process that goes far beyond a simple blood count. Because the symptoms can look like many other immune issues, doctors must use a combination of genetic sequencing and specialized “functional” tests to confirm the diagnosis.

Establishing the Diagnosis

A diagnosis of CD70 deficiency requires expert review of genetic, functional, and clinical evidence:

1. Genetic Proof: Identifying two mutations (biallelic variants) in the CD70 gene that are classified as pathogenic or likely pathogenic, and confirmed to be in trans ^[1][2]. Note that two variants of uncertain significance (VUS) do not establish the diagnosis.
2. Protein Proof: Showing through specialized testing that the CD70 protein is either missing, severely reduced, or cannot bind to its partner, CD27 ^[1][3].
3. Clinical Proof: A history matching the condition, such as impaired control of the Epstein-Barr Virus (EBV) or recurrent infections ^[4][1].

Specialized Laboratory Testing

Standard blood tests, such as total white blood cell and lymphocyte counts, often come back looking relatively normal ^[1]. Instead, doctors must use more advanced tools:

Flow Cytometry (The Protein “Snapshot”)

This test uses lasers to count and examine proteins on the surface of individual cells.

• Activation is Key: Because the CD70 protein is primarily expressed when the immune system is “awake,” doctors must stimulate the cells in the lab (creating activated T-cell blasts or B cells) before testing ^[1][4].
• What to Look For: In CD70 deficiency, the protein will be absent or severely reduced on these activated cells ^[3][4].
• Binding Assays: If the protein is present but doesn’t work, a CD27 binding assay is used to see if the CD70 can successfully attach to its receptor ^[1].

EBV Monitoring

Since the immune system struggles to clear EBV, monitoring the virus is a lifelong task.

• Quantitative PCR: This measures the “viral load” (the amount of virus DNA) in the blood ^[5].
• Compartments: Doctors may check both plasma (the liquid part of blood) or whole blood. It is vital to understand that values from plasma and whole blood are not interchangeable, and interpretation depends on the assay and lab ^[6][7]. Using the same lab and specimen type is vital for accurately tracking trends.
• Tissue Biopsy: If there is a suspicious lump, a biopsy may be performed using EBER in-situ hybridization to detect EBV within the cells ^[8][9]. A positive EBER stain does not by itself prove lymphoma; tissue architecture and immunophenotyping are required.

Reading the Immune “Phenotype”

The pathology report may include a detailed breakdown of immune cells, called a phenotype. While findings vary, these specific patterns are sometimes observed:

• Low Memory B Cells: The body may struggle to create the cells that “remember” past infections ^[1].
• Reduced Effector-Memory T Cells: Specifically, the CD8+ T cells that target viruses are sometimes low in number, or show variable expression of markers like 2B4 and NKG2D, which are supportive research findings ^[1][10].
• Variable Antibodies: Some patients have hypogammaglobulinemia (low antibody levels), while others may have normal levels but their antibodies don’t work effectively against vaccines ^[1][4].

Completeness Checklist to Review

You can use this list to review the medical records. If any of these are missing, it is a good topic for your next specialist visit.

• [ ] Genetic Report: Does it show biallelic (two) pathogenic mutations in the CD70 gene?
• [ ] Segregation Analysis: Have both parents been tested to confirm each passed down one mutation? ^[2]
• [ ] Flow Cytometry: Was CD70 expression tested on activated cells? ^[1]
• [ ] EBV Viral Load: What specific PCR specimen type is being used to track trends? ^[5]
• [ ] B Cell Subset Panel: Does the report mention the levels of memory B cells? ^[1]
• [ ] Quantitative Immunoglobulins: Are levels of IgG, IgA, and IgM documented? ^[1]