# MPGN and Infection-Related GN: A Pattern Needs a Cause

Not every low-complement GN is self-limited postinfectious disease. The diagnosis should explain the timing, pathology, and subsequent course.

![Infographic: MPGN and Infection-Related GN: A Pattern Needs a Cause](https://urinenephrology.org/visual-reference/images/mastery-mpgn-infection.png?v=20261003c)

## MPGN is a pattern, not one disease

Use immunofluorescence to separate immunoglobulin/immune-complex-predominant injury from C3-dominant injury. Immune-complex patterns prompt infection, autoimmune, and monoclonal evaluation; C3-dominant patterns raise complement-pathway questions. Electron microscopy adds localization and structure rather than replacing the etiologic search.

## Recognize the clinical context

Hematuria, proteinuria, low complement, AKI, and a preceding or ongoing infection help organize the differential but are not individually diagnostic.

## Investigate persistent drivers

Use infection assessment, monoclonal studies, complement evaluation, and biopsy interpretation according to the pattern and patient context.

## Treat active infection first

When infection is the driver, antimicrobial therapy and source control are central. Immunosuppression can be hazardous without a clear rationale.

## Reopen the diagnosis when recovery stalls

Persistent low complement, hematuria, proteinuria, or worsening function after an apparent infection-related episode should prompt reassessment for ongoing infection, complement-mediated disease, or another lesion. Do not assume every postinfectious presentation is self-limited or escalate immunosuppression before checking for an uncontrolled source.

## Avoid a premature label

Not every low-complement GN is self-limited postinfectious disease. The diagnosis should explain the timing, pathology, and subsequent course.

## Source lessons

- [mpgn](https://urinenephrology.org/mastery/glomerular/mpgn.html)
- [post infectious gn](https://urinenephrology.org/mastery/glomerular/post-infectious-gn.html)

Read alongside the full lessons; the findings and decisions shown here require the stated clinical context.