Understanding Your Pathology & Lab Reports

When you receive your pathology and lab reports, the language can seem like a different dialect. For IgG4-related retroperitoneal fibrosis (IgG4-RPF), the diagnosis isn’t based on one single “positive” or “negative” result. Instead, doctors look for a specific pattern of findings in your tissue and blood.

The Pathology “Triad”

Pathologists look for three main microscopic features to confirm IgG4-RD. This is often called the “histopathologic triad”:

1. Dense Lymphoplasmacytic Infiltrate: This simply means the tissue is packed with a high number of lymphocytes and plasma cells (types of white blood cells) ^[1][2].
2. Storiform Fibrosis: This is a very specific type of scarring. “Storiform” comes from the Latin word for a woven mat. Under a microscope, the scar tissue looks like it has been woven together in a circular or “wagon-wheel” pattern ^[1][3].
3. Obliterative Phlebitis: This occurs when the inflammatory cells and scar tissue squeeze small veins until they are completely closed or “obliterated” ^[1][4].

The “Fingerprint”: IgG4+ Plasma Cells

To confirm the disease is specifically IgG4-related, the pathologist uses a special stain called immunohistochemistry (IHC) to count the IgG4-positive plasma cells ^[3][5].

• The Count: In the retroperitoneum, doctors typically look for at least 10 IgG4+ plasma cells per “high-power field” (the area visible under the microscope at high magnification) ^[6].
• The Ratio: They also calculate the IgG4+/IgG+ ratio. If more than 40% of the total plasma cells in the tissue are producing IgG4, it strongly supports the diagnosis ^[6][6].

Why Your Blood Work Might Be Normal

You might be surprised to find your serum IgG4 (the level of IgG4 in your blood) is within the normal range, even after a biopsy confirms the disease.

• Serum vs. Tissue: About 30% to 50% of people with biopsy-proven IgG4-RD have normal serum IgG4 levels ^[7][8]. The disease can be very active in your organs even if it doesn’t “spill over” into your bloodstream in large amounts ^[7][9].
• Monitoring: Because of this, a normal blood test doesn’t mean you are in the clear. Doctors will rely more on your symptoms and imaging (like CT or MRI scans) to track your progress ^[9][10].

Pathology Report Completeness Checklist

When reviewing your pathology report, check for these specific data points. If they are missing, you may want to ask if the pathologist can provide them:

• [ ] IgG4+ cell count (e.g., “X cells per HPF”) ^[6].
• [ ] IgG4+/IgG+ ratio (e.g., “>40%”) ^[6].
• [ ] Mention of storiform fibrosis ^[1].
• [ ] Mention of obliterative phlebitis ^[1].
• [ ] Exclusion of malignancy: A statement that no cancer cells (like lymphoma) were seen ^[11][12].

Note: If you were taking steroids before your biopsy, the cell counts might appear lower than they actually are, as these medications quickly clear immune cells from the tissue ^[13].