Symptoms and Signs of Renal TMA
Renal thrombotic microangiopathy presents with the classic triad of microangiopathic hemolytic anemia (non-immune hemolysis with negative Coombs test, elevated LDH, reduced haptoglobin), thrombocytopenia (platelets <150,000/mm³ or 25% reduction), and renal involvement (elevated creatinine, hematuria, and/or proteinuria), though importantly, not all three features are clearly present at onset in almost 50% of cases. 1
Core Clinical Features
Hematologic Manifestations
Microangiopathic hemolytic anemia with:
- Negative direct Coombs test (non-immune hemolysis)
- Elevated lactate dehydrogenase (LDH)
- Reduced haptoglobin levels
- Schistocytes on peripheral blood smear (though >1% is diagnostic, their absence should NOT exclude TMA due to low test sensitivity) 1
Thrombocytopenia: Platelet count <150,000/mm³ or a 25% reduction from baseline 1
Renal Manifestations
- Acute kidney injury with elevated creatinine (mean ~3.1-3.3 mg/dL in severe cases) 2, 3, 4
- Hematuria: Microscopic hematuria present in the majority of patients (86% in one series) 3
- Proteinuria: Variable, ranging from minimal to significant (>3 g/day in severe cases) 3, 4
Cardiovascular Manifestations
- Severe hypertension: Often presenting with systolic BP 200-280 mmHg and diastolic BP 110-180 mmHg in hypertension-associated TMA 2, 3
- Hypertension present in approximately 75% of cases 4
Neurological Manifestations (10-20% of patients)
When neurological involvement is suspected, specific features include: 1
- Seizures
- Encephalopathy
- Motor symptoms and generalized weakness
- Vision changes
- Neurological symptoms warrant EEG and brain MRI showing bilateral symmetrical hyperintensities of basal ganglia on FLAIR and T2-weighted sequences, with possible involvement of cerebral peduncles, caudate nuclei, putamen, thalami, hippocampi, insulae, and brainstem 1
Critical Diagnostic Pitfalls
Incomplete Presentation
A critical caveat: In almost 50% of cases at onset, the complete triad (hemolytic anemia, thrombocytopenia, renal involvement) is NOT clearly present. 1 This means you cannot wait for all three features to appear before considering TMA.
Schistocyte Sensitivity
The absence of schistocytes should NOT exclude an early diagnosis of TMA due to the low sensitivity of this test 1. While >1% schistocytes is a robust threshold favoring TMA diagnosis, their absence does not rule it out.
Post-Transplant Presentation
Following renal transplant, the absence of marked thrombocytopenia or significant anemia should NOT exclude a TMA diagnosis 1. Renal-limited TMA can occur without systemic hematologic manifestations 5.
Essential Initial Laboratory Workup
When ANY patient presents with anemia plus thrombocytopenia in the emergency setting, immediately determine: 1
- Haptoglobin (reduced)
- Indirect bilirubin (elevated)
- LDH (elevated)
- Direct Coombs test (must be negative)
Once TMA is suspected, urgently obtain: 1
- ADAMTS13 activity (to distinguish TTP, where activity is <10 IU/dL)
- Stool testing for verocytotoxin-producing E. coli (VTEC)
Special Populations
Pediatric Considerations
- In children with diarrhea: Short duration of diarrhea or concomitant appearance of diarrhea and HUS suggests atypical HUS rather than STEC-HUS (which typically appears 4-5 days after diarrhea onset) 1
- First year of life: Consider mutations in complement-unrelated genes (DGKE, WT1) and cobalamin metabolism disorders 1
Lupus-Associated TMA
- May be the sole renal complication in SLE 4
- NOT usually associated with hemolytic microangiopathic anemia 4
- Frequently associated with lupus anticoagulant (63% in one series) and antiphospholipid antibodies 4
- Can present with predominantly renal involvement in the absence of persistent thrombocytopenia 6
- Associated with significantly poorer renal function recovery and higher risk of requiring renal replacement therapy 7