Hospital Frequency of Thrombotic Microangiopathy (TMA)
TMA is relatively uncommon in hospitals, with primary TMA (TTP and aHUS) representing only 6% of all TMA cases, while secondary TMA accounts for 94% of cases encountered. 1
Incidence Data
Overall TMA Frequency
In a large retrospective study of 564 consecutive patients with adjudicated TMA over an 8-year period (2009-2016) across four hospitals, primary thrombotic microangiopathies occurred in only 33 of 564 patients (6%), broken down as:
- Thrombotic thrombocytopenic purpura (TTP): 18 of 564 (3%)
- Atypical hemolytic uremic syndrome (aHUS): 18 of 564 (3%)
- Secondary TMA: 531 of 564 (94%) 1
Specific Population Incidence
Among nephrology department inpatients, the incidence of complement-mediated TMA was 6.4 per 1,000 patients per year 2, indicating that while uncommon, it represents a meaningful proportion of nephrology admissions.
In the dialysis population, TMA incidence in the first year of dialysis was 0.5% overall among 272,024 Medicare patients. However, this varied dramatically by underlying cause:
- Patients with renal failure due to HUS: 11.3% in the first year, then 4.5% per year thereafter
- Patients without HUS: 0.3% per year (constant rate) 3
Global Incidence of TTP
The global incidence of immune-mediated TTP (iTTP) is 1-6 cases per million people per year 4, making it a rare but critical diagnosis that requires immediate recognition.
Secondary TMA Causes in Hospitals
Secondary TMA is far more common than primary TMA and frequently involves multiple concurrent triggers (present in 57% of secondary TMA cases versus 19% of primary cases). 1
The most common causes of secondary TMA encountered in hospitals include:
- Pregnancy: 35% (representing 11 of 1,000 pregnancies)
- Infections: 33%
- Drugs: 26%
- Malignancies: 19%
- Transplantations: 17%
- Autoimmune diseases: 9%
- Shiga toxin (E. coli): 6%
- Malignant hypertension: 4% 1
Cancer-Associated TMA
Among hospitalized TMA patients, 19.1% have concurrent malignancy 5. In cancer patients with TMA:
- Two-thirds have solid tumors (pancreas, lung, breast, colorectal, hepatobiliary—half metastatic)
- One-third have hematological malignancies (lymphoma, acute leukemia, multiple myeloma)
- Hospital mortality is significantly higher (16.6% vs. 6.1% in non-cancer TMA patients)
- Mortality reaches 30% in transplant recipients 5
Clinical Recognition Challenges
Diagnostic delays are common, particularly in older patients. In a database study of patients seen 2000-2016, the median time from hospital admission to diagnosis was:
- 3 days [IQR 1-7] in patients ≥60 years old
- 1 day [IQR 1-3] in younger patients 6
In a study of 2,992 acute TTP patients (2012-2019), 47.6% of patients ≥60 years old experienced a TPE delay of ≥2 days from symptom onset, compared to 31.9% in younger adults. 6
Key Clinical Pitfall
The vast majority of TMA cases hospitals encounter are secondary, not primary. 1 This means clinicians must systematically evaluate for pregnancy, infection, drugs, malignancy, and transplantation as triggers, rather than immediately assuming primary TTP or aHUS. However, TTP must still be considered first in any TMA presentation because of its high mortality without immediate treatment, and therapy should be initiated before ADAMTS13 results are available. 6