A 38 year old woman presents to the ER with 1 week of fevers and malaise. Serum creatinine 1 year ago was 54 micromol/L. 2 days ago when measured in a walk in clinic it was 97 micromol/L. In the ER, her blood pressure is 160/104 mm Hg and serum creatinine is 173 micromol/L. Urinalysis reveals 3+ protein and 3 + blood. Her microscopy shows red blood cells and red blood cell casts.
What would be in your differential diagnosis? What tests would you order at this point?
This patient has acute renal failure. Given the associated hypertension, proteinuria and hematuria, this patient appears to have the nephritic syndrome. The presence of red blood cell casts make us much more confident about the diagnosis of a glomerulonephritis.
We believe this woman has a glomerulonephritis, but the differential diagnosis still remains broad. It would include, but is not limited to, such conditions as:
- Lupus Nephritis
- Post-streptococcal glomerulonephritis
- ANCA (Anti-Neutrophil Cytoplasmic Antibody) -associated vasculitis, such as:
- Wegener’s Granulomatosis
- Microscopic Polyangiitis
- Renal-limited vasculitis
- Anti-Glomerular Basement Membrane (Anti-GBM):
- Antibody disease
- Goodpasture’s disease (if associated with pulmonary hemorrhage)
- IgA Nephritis
- Henoch-Schonlein Purpura
- Endocarditis-associated glomerulonephritis
- Cryoglobulinemic glomerulonephritis
In order to help make a specific diagnosis, a variety of tests can be ordered, though individual nephrologists may not include all of these in the initial workup. These could include:
- Anti-nuclear antibody (ANA)
- C3 and C4 (complements)
- P-ANCA (perinuclear ANCA)
- C-ANCA (cytoplasmic ANCA)
- Anti-GBM (glomerular basement membrane) antibody
- Cryoglobulins
- Hepatitis C antibody
Additional testing might also be necessary to look for other manifestations of the underlying disease. For example, in patients with ANCA vasculitis or Goodpasture’s disease, one might find pulmonary hemorrhage – therefore a chest x-ray would be useful.
In the setting of acute renal failure and a rapidly rising creatinine, most nephrologists will also order a CBC +/- a blood film to consider the diagnosis of Hemolytic Uremic Syndrome (HUS) and/or Thrombotic Thrombocytopenia Purpura (TTP). They will generally also order a serum protein immunoelectrophoresis to consider the diagnosis of multiple myeloma with acute cast nephropathy.
In acute renal failure, you would also want to look for potential complications of renal failure and would therefore order:
- Electrolytes (especially K and HCO3)
- Calcium
- Phosphate
Given that most of these patients will require a kidney biopsy, one should consider INR and PTT as well as a renal ultrasound.
