# AIN and GN: When Tissue Changes the Decision

Histology, immunofluorescence, electron microscopy, clinical context, and the trajectory should tell a coherent story. A biopsy pattern still needs an etiologic explanation.

![Infographic: AIN and GN: When Tissue Changes the Decision](https://urinenephrology.org/visual-reference/images/mastery-ain-biopsy.png?v=20261003c)

## Different compartments

Interstitial inflammation and glomerular inflammation can both cause AKI, but their causes, urine patterns, and treatment pathways differ. Mixed injury is possible.

## Use the pattern to change the question

A new culprit drug with pyuria and modest proteinuria supports AIN; RBC casts, substantial albuminuria, or pulmonary–renal features raise concern for GN. These patterns overlap. Absence of rash, fever, or eosinophilia cannot safely rule out drug-associated AIN.

## Avoid weak rule-out tests

Urine eosinophils have limited diagnostic performance. Serologies and urine microscopy can support a hypothesis, but none replaces clinical reasoning or automatically establishes pathology.

## Biopsy when the result changes treatment

Persistent or severe unexplained AKI, competing diagnoses, or a proposed course of immunosuppression creates a stronger reason for tissue. Discuss bleeding risk and expected diagnostic yield. Do not use urine eosinophils as a substitute for biopsy or as a reason to dismiss a plausible diagnosis.

## Address the cause

Stop plausible offending drugs and investigate infection or systemic disease. Immunosuppression decisions require diagnosis, timing, chronicity, and patient-specific risk assessment.

## Interpret the whole specimen

Histology, immunofluorescence, electron microscopy, clinical context, and the trajectory should tell a coherent story. A biopsy pattern still needs an etiologic explanation.

## Source lessons

- [acute interstitial nephritis comprehensive](https://urinenephrology.org/mastery/aki-advanced/acute-interstitial-nephritis-comprehensive.html)
- [ain gn diagnostic methodologies review](https://urinenephrology.org/mastery/aki-advanced/ain-gn-diagnostic-methodologies-review.html)

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