PLASMIC Score Calculator — TTP Risk Assessment
The PLASMIC score is a validated clinical prediction tool for estimating the probability of severe ADAMTS13 deficiency (<10%) in patients presenting with thrombotic microangiopathy and suspected thrombotic thrombocytopenic purpura (TTP). It uses seven readily available clinical and laboratory variables to stratify patients into low, intermediate, and high probability categories, guiding urgent treatment decisions including plasma exchange initiation.
About
The PLASMIC score was developed by Bendapudi et al. and published in The Lancet Haematology in 2017. It was derived from a cohort of 214 patients with thrombotic microangiopathy (TMA) from three academic medical centers and externally validated in an independent cohort of 97 patients. The score incorporates seven clinical and laboratory variables: Platelet count <30 x10⁹/L, hemolysis (reticulocyte count >2.5%, undetectable haptoglobin, or indirect bilirubin >2 mg/dL), Active cancer (within 1 year), history of Solid organ or stem cell transplant, Mean corpuscular volume (MCV) <90 fL, International normalized ratio (INR) <1.5, and Creatinine <2.0 mg/dL (177 µmol/L). The acronym PLASMIC represents the seven variables: Platelets, hemolysis, Active cancer, Stem cell/solid organ transplant, MCV, INR, Creatinine. Two variables (active cancer and transplant) are negative predictors that subtract from the total score. The total score ranges from 0 to 7 after flooring negative values at 0. Risk stratification: 0-4 (low probability of severe ADAMTS13 deficiency <5%), 5 (intermediate probability 5-70%), and 6-7 (high probability >70%). The score has demonstrated excellent discrimination with a c-statistic of 0.94 for severe ADAMTS13 deficiency in the original validation cohort.
Formula
PLASMIC = Platelets <30 (1) + Hemolysis (1) - Active Cancer (1) - Transplant (1) + MCV <90 (1) + INR <1.5 (1) + Creatinine <2.0 (1)
The PLASMIC score is calculated by summing points from seven clinical variables. (1) Platelet count <30 x10⁹/L contributes +1 point. (2) Evidence of hemolysis — reticulocyte count >2.5%, undetectable haptoglobin, or indirect bilirubin >2 mg/dL — contributes +1 point. (3) Active cancer within the past year contributes -1 point (subtracts from the total). (4) History of solid organ or stem cell transplant contributes -1 point (subtracts from the total). (5) Mean corpuscular volume (MCV) <90 fL contributes +1 point. (6) INR <1.5 contributes +1 point. (7) Creatinine <2.0 mg/dL (177 µmol/L) contributes +1 point. If the score after adding all variables results in a negative value, it is floored at 0. The final score ranges from 0-7. Risk stratification: Low risk (score 0-4): <5% probability of severe ADAMTS13 deficiency — consider alternative TMA etiologies. Intermediate risk (score 5): 5-70% probability — send ADAMTS13 activity and consider initiating plasma exchange if clinical suspicion is high. High risk (score 6-7): >70% probability — start plasma exchange immediately and high-dose corticosteroids without waiting for ADAMTS13 results. The two negative predictors (active cancer and transplant) reflect that these conditions cause TMA through ADAMTS13-independent mechanisms (endothelial injury and complement dysregulation).
Score Interpretation
The PLASMIC score is the most validated clinical prediction tool for identifying patients with thrombotic microangiopathy who have severe ADAMTS13 deficiency (immune-mediated TTP). Its primary clinical impact is in guiding urgent decision-making about plasma exchange (PLEX) initiation. TTP is a medical emergency with mortality exceeding 90% if untreated, but PLEX reduces mortality to 10-20%. However, PLEX is resource-intensive, associated with procedural complications, and may be unnecessary for TMA patients who do not have TTP. The PLASMIC score enables early risk stratification at the bedside using readily available laboratory values, helping clinicians initiate PLEX promptly in high-probability patients while avoiding unnecessary PLEX in low-probability patients where alternative TMA etiologies (drug-induced TMA, complement-mediated HUS, DIC) should be pursued. The score's c-statistic of 0.94 for predicting severe ADAMTS13 deficiency demonstrates excellent discrimination. Key validation studies: The French TMA Reference Center validated the score in 550 patients, confirming its high negative predictive value (98.5% for low-risk category). A meta-analysis of 7 validation studies including 1,023 patients found pooled sensitivity of 91% and specificity of 89% for severe ADAMTS13 deficiency at the high-risk cutoff (score ≥6). Limitations include potential misclassification of patients with mild ADAMTS13 deficiency (10-50% activity) and reduced performance in cancer/transplant-associated TMA populations where the negative predictors may overcorrect.
Low Probability (<5%) — 0–4
Score 0-4: Low probability of severe ADAMTS13 deficiency (<5%). Consider alternative TMA etiologies.
Management: Low probability of severe ADAMTS13 deficiency. Consider alternative diagnoses (HUS, DIC, drug-induced TMA). Hematology consultation recommended for further workup.
Intermediate Probability (5-70%) — 5–5
Score 5: Intermediate probability of severe ADAMTS13 deficiency (5-70%). Send ADAMTS13 activity urgently.
Management: Intermediate probability. Send ADAMTS13 activity level urgently. Consider starting plasma exchange while awaiting ADAMTS13 results if clinical suspicion high. Start high-dose corticosteroids (methylprednisolone 1 g/day).
High Probability (>70%) — 6–7
Score 6-7: High probability of severe ADAMTS13 deficiency (>70%). Start treatment immediately.
Management: High probability of severe ADAMTS13 deficiency. Start plasma exchange (PLEX) immediately — do not wait for ADAMTS13 results. Start high-dose corticosteroids. Consider rituximab if refractory. Platelet transfusion is generally contraindicated unless life-threatening bleeding.
Reference Ranges
| Population | Normal Range | Notes |
|---|---|---|
| Patients with TMA and suspected TTP | 0-7 points | 0-4 = Low risk (<5% severe ADAMTS13 deficiency), 5 = Intermediate (5-70%), 6-7 = High (>70%). Score ≥6 has 91% sensitivity and 89% specificity for severe ADAMTS13 deficiency. |
Dr. Mahmoud El-Sayed
Dr. Mahmoud El-Sayed is a hematology consultant with expertise in thrombotic microangiopathies and hemostasis.
View medical review board & editorial policy →Example Calculation
A 35-year-old woman presents with acute onset of confusion, petechiae, and mild jaundice. Laboratory findings: platelet count 18 x10⁹/L, hemoglobin 8.5 g/dL, reticulocyte count 4.2%, haptoglobin undetectable, indirect bilirubin 2.8 mg/dL, MCV 92 fL, INR 1.1, creatinine 1.2 mg/dL. No history of cancer or transplant. PLASMIC score: Platelets <30 (+1), Hemolysis — reticulocytes >2.5% (+1), Active cancer (-0), Transplant (-0), MCV <90 (92 fL, does not meet criteria, +0), INR <1.5 (+1), Creatinine <2.0 (+1) = Total Score 4/7 (Low risk, <5% probability of severe ADAMTS13 deficiency). Despite the low PLASMIC score, given the strong clinical suspicion for TTP (neurological involvement, severe thrombocytopenia, hemolysis), the clinician sends ADAMTS13 activity and initiates PLEX empirically due to the high mortality of missed TTP. ADAMTS13 results return at 35% activity (not severe deficiency), and the patient is diagnosed with complement-mediated HUS (aHUS), treated with eculizumab. This case illustrates the PLASMIC score's high negative predictive value — the low score correctly predicted absence of severe ADAMTS13 deficiency. However, clinical judgment remains critical in treatment decisions.
Related Conditions
Related Medications
Common Mistakes
Applying the PLASMIC score to patients with established TTP diagnosis rather than undifferentiated TMA
The PLASMIC score was designed for patients presenting with thrombotic microangiopathy (TMA) of unclear etiology — defined by microangiopathic hemolytic anemia (schistocytes on peripheral smear) and thrombocytopenia. It should not replace ADAMTS13 testing in patients with high clinical suspicion for TTP, nor should it be applied when the TMA etiology is already known.
Misinterpreting the negative predictors — thinking active cancer or transplant should exclude TTP entirely rather than reducing its probability
Active cancer and transplant are negative predictors, each subtracting 1 point, but they do not rule out TTP. Patients with cancer or transplant can still develop immune-mediated TTP, though alternative TMA mechanisms (drug-induced, complement-mediated) are more likely. The score should be interpreted in clinical context — a cancer patient with high clinical suspicion still deserves ADAMTS13 testing.
Frequently Asked Questions
What is the PLASMIC score and when should it be used?
Should plasma exchange be started if the PLASMIC score is low (0-4)?
References
- Bendapudi PK, Hurwitz S, Fry A, et al. Derivation and external validation of the PLASMIC score for the prediction of severe ADAMTS13 deficiency in patients with thrombotic microangiopathy. Lancet Haematol. 2017;4(4):e157-e164. PubMed
- Coppo P, Cuker A, George JN. Thrombotic thrombocytopenic purpura: evidence-based evaluation of clinical criteria for the diagnosis and risk stratification. J Clin Apher. 2019;34(4):419-427.
- Scully M, Hunt BJ, Benjamin S, et al. Guidelines on the diagnosis and management of thrombotic thrombocytopenic purpura and other thrombotic microangiopathies. Br J Haematol. 2012;158(3):323-335. PubMed