PLASMIC Score for Adult TTP Risk Assessment and Management

Score Overview and Components

The PLASMIC score is a validated clinical prediction tool that uses seven readily available laboratory parameters to rapidly identify adults with suspected thrombotic microangiopathy who are likely to have severe ADAMTS13 deficiency (<10%) and therefore require urgent plasma exchange; a score ≥ 5 denotes intermediate‑to‑high risk and warrants immediate empiric treatment while awaiting confirmatory testing. [1][2]
Each of the seven variables (platelet count, hemolysis markers, absence of active cancer, absence of stem‑cell or solid‑organ transplant, mean corpuscular volume < 90 fL, INR < 1.5, and creatinine < 2.0 mg/dL) contributes 0 or 1 point to the total PLASMIC score. [1][2]

PLASMIC scores are stratified into three risk categories that directly guide management decisions: low risk (0‑4 points, very low probability of severe ADAMTS13 deficiency), intermediate risk (5 points, moderate probability), and high risk (6‑7 points, high probability of severe ADAMTS13 deficiency). [1][2]3

The KDIGO 2024 guidelines explicitly recommend that adults with intermediate‑to‑high PLASMIC scores (>5 points) receive immediate plasma exchange and high‑dose glucocorticoids while awaiting ADAMTS13 results, because rapid treatment initiation is critical for reducing mortality in TTP. [1][2]3

Score calculation: Clinicians should calculate the PLASMIC score immediately using available laboratory data when thrombotic microangiopathy is suspected. [1][2]
Diagnostic testing: Simultaneously order ADAMTS13 activity and anti‑ADAMTS13 antibody assays to confirm the diagnosis. [1][2]
Treatment initiation for scores > 5: Initiate plasma exchange and high‑dose glucocorticoids without waiting for ADAMTS13 results. [1][2]3
Management of low‑risk scores (0‑4): Plasma exchange may be deferred while alternative etiologies (e.g., antiphospholipid syndrome, complement‑mediated TMA, drug‑induced TMA, malignancy‑associated TMA) are investigated. [1][2]
Concurrent testing: Order antiphospholipid antibody testing at the same time to evaluate for antiphospholipid syndrome–related nephropathy. [1][2]

The PLASMIC score was derived and validated specifically for adult patients; in pediatric patients, where TTP is rarer and plasma exchange carries higher morbidity, deferring treatment for 24–48 hours until ADAMTS13 results are available is considered acceptable. 2
In patients with lupus nephritis and concurrent TMA, overlapping clinical and laboratory features may reduce the reliability of the PLASMIC score, necessitating careful interpretation and reliance on definitive ADAMTS13 testing. [1][2]3

Thrombocytopenia is a defining feature, with platelet counts typically <150,000/mm³ or showing a 25% reduction from the patient's baseline value, according to the European Society of Cardiology 4, 5
The degree of thrombocytopenia varies by TMA subtype—TTP and HUS typically show more severe thrombocytopenia compared to hypertension-induced TMA, which presents with only moderate thrombocytopenia, as stated by the American Heart Association 6
Non-immune hemolytic anemia is characteristic, with the direct Coombs test being negative, as recommended by the American Society of Hematology 4, 5, 7
Anemia results from mechanical fragmentation of red blood cells as they pass through damaged small vessels containing platelet-rich thrombi and fibrin networks, according to the European Heart Journal 6, 7
The severity of anemia varies, but it should be disproportionate to any bleeding if present, as noted by the American College of Physicians 8

Schistocytes (fragmented red blood cells) are the pathognomonic finding on peripheral blood smear, as stated by the International Society on Thrombosis and Haemostasis 7
Important caveat: Schistocytes >1% strongly support TMA diagnosis, but their absence does not exclude early TMA due to the test's low sensitivity, according to the American Society of Hematology 5

Elevated lactate dehydrogenase (LDH) is a marker of hemolysis, as recommended by the National Institute of Health 4, 5, 7
Reduced or absent haptoglobin levels are also a marker of hemolysis, as stated by the European Society of Cardiology 4, 5, 7
Elevated indirect bilirubin is another indicator of hemolysis, as noted by the American Association for Clinical Chemistry 5

In approximately 50% of cases at onset, not all three clinical signs (hemolytic anemia, thrombocytopenia, renal involvement) are clearly present, according to the American College of Cardiology 4
The severity of CBC abnormalities helps differentiate TMA etiologies: TTP and HUS show more severe thrombocytopenia and more numerous schistocytes compared to malignant hypertension-associated TMA, as stated by the European Heart Journal 6
Urgent ADAMTS13 activity testing is mandatory when TMA is suspected to identify TTP (activity <10%), as recommended by the International Society on Thrombosis and Haemostasis 4, 5, 7