What investigations does she need?
- AKI is broadly broken down to pre-renal, intrinsic, and post renal causes and these should be investigated
- Pre-renal is typically due to heamodynamic disturbance, post renal is typically due to obstruction of the drainage of urine. Renal tract ultrasound should be undertaken to rule out obstruction.
- Intrinsic causes of AKI are often vague and require careful consideration of medications and assessment of the urine dip for signs of inflammation.
In this case there is evidence of inflammation in the form of blood and protein in the urine and this should prompt a suspicion for vasculitis/glomerulonephritis and the following tests should be sent:
- ANA – for SLE
- DS DNA – for SLE
- ANCA – for ANCA vasculitis
- Anti GBM- for anti – GBM disease
- Complement – for SLE and glomerulonephritis
- Serum Electrophoresis- for myeloma
Urine should also be sent for spot urine protein-creatinine ratio – 24 hour urine collection for protein is archaic, and has been shown to be equivalent to a spot sample for protein quantification.
A renal biopsy may be required if there is suspicion of vasculitis or glomerulonephritis, or if renal failure persists without clear cause.
In this case presentation the patient was admitted to ICU for haemodiafiltration to control her potassium. Despite initial fluid removal of 100ml/hr her oxygenation deteriorated and repeat chest X-ray showed diffuse alveolar infiltrates. The nurses noted small volume haemoptysis overnight. 24 hours after admission to the intensive care, the immunology lab contacted the intensive care unit to inform them that the patient was found to have a positive ANCA with antibodies directed to PR3.
Although rare, vasculitis involving the kidneys is an important cause of AKI which if not diagnosed promptly, leads to irreversible damage to the kidneys and end stage renal failure. It has an incidence of around 20 cases per million population per year occurring in all ages with a peak age of onset of 55-70 years. It is an autoimmune condition leading to inflammation and damage to the filtering unit of the kidney, the glomeruli. It is a Rapidly Progressive GlomeruloNephritis (RPGN). The most common causes of RPGN are ANCA vasculitis or anti-glomerular basement membrane disease (Anti-GBM). The key feature in this case is a urine dip that is positive for blood which suggests active inflammation within the glomeruli and blood leaking through the damaged basement membrane. Blood tests for ANCA and Anti-GBM should be sent early as possible, as delays in treatment can lead to irreversible end stage renal failure.