PLASMIC Score Calculator — TTP and Severe ADAMTS13 Deficiency
Estimate the pretest probability of severe ADAMTS13 deficiency (activity under 10 percent) in an adult with thrombotic microangiopathy, using seven laboratory and history variables that are available at the bedside while the ADAMTS13 assay is still pending.
When to use it
Use only in adults who already have thrombocytopenia (platelets under 150 x10^9 per litre) and schistocytes on the peripheral smear. A score of 5 or more supports starting therapeutic plasma exchange while awaiting ADAMTS13. A score of 0 to 4 makes TTP unlikely and should redirect the workup toward atypical HUS and other causes of thrombotic microangiopathy.
Formula
One point each for: platelets under 30 x10^9 per litre; hemolysis (reticulocytes over 2.5 percent, undetectable haptoglobin, or indirect bilirubin over 2.0 mg/dL); no active cancer; no solid-organ or stem-cell transplant; MCV under 90 fL; INR under 1.5; creatinine under 2.0 mg/dL. Total 0 to 7.
Category
Systemic Diseases & Scores. Related searches: plasmic score, plasmic score calculator, ttp calculator, adamts13 deficiency, thrombotic thrombocytopenic purpura, thrombotic microangiopathy.
References
Bendapudi PK, et al. Derivation and external validation of the PLASMIC score for rapid assessment of adults with thrombotic microangiopathies: a cohort study. Lancet Haematol. 2017;4(4):e157-e164
Paydary K, et al. Diagnostic accuracy of the PLASMIC score in patients with suspected thrombotic thrombocytopenic purpura: a systematic review and meta-analysis. Transfusion. 2020;60(9):2047-2057
Li A, et al. External validation of the PLASMIC score: a clinical prediction tool for thrombotic thrombocytopenic purpura diagnosis and treatment. J Thromb Haemost. 2018;16(1):164-169
Common clinical questions
What does a PLASMIC score of 5 mean? A score of 5 is the intermediate band, carrying roughly a 6 percent probability (range 5 to 24 percent) of ADAMTS13 activity below 10 percent. Bendapudi 2017 supports beginning therapeutic plasma exchange at 5 or more while awaiting the assay, but Li 2017 found no significant survival benefit from plasma exchange in the 0 to 5 group, so weigh the decision with hematology rather than treating 5 as automatic.
Can the PLASMIC score rule out TTP? At a cutoff of 5 or more the score is highly sensitive (0.99) with a negative predictive value of 0.99 at 35 percent prevalence, so a score below 5 makes severe ADAMTS13 deficiency very unlikely. Specificity at that cutoff is only 0.57, so it over-triages. A score below 6 is not sensitive enough to exclude TTP on its own, and the score never replaces ADAMTS13 testing.
Does a low PLASMIC score point toward atypical HUS? Often, yes. Atypical HUS is invariably associated with ADAMTS13 above 10 percent, and roughly 85 percent of patients with confirmed aHUS score 5 or below. Using a cutoff of 5 or below to flag probable aHUS in a patient with confirmed thrombotic microangiopathy and renal impairment gave sensitivity 86.5 percent and specificity 71.4 percent. Treat a low score as a redirect, not as reassurance.
Is the PLASMIC score valid in children? No. The score was derived and validated in adults, and the creatinine threshold of 2.0 mg/dL does not hold in children, where it can indicate severe kidney dysfunction rather than roughly half of normal function. A modified pediatric version, PLASMICkid, substitutes an eGFR above 50 mL/min/1.73m2 for the creatinine criterion.
How accurate is the PLASMIC score across centres? External validations report areas under the curve from about 0.80 to 0.94 across Canadian, Italian, Taiwanese, Korean and US cohorts, and it outperformed the Bentley and French TMA Reference Center scores head to head. Performance is not uniform: Moosavi 2020 and Reddy 2018 both found it insufficiently discriminatory to use alone at their institutions.
About NephroMind
This calculator is part of NephroMind, a free clinical decision-aid platform from the Arab Society of Nephrology and Renal Transplantation (ASNRT) — over 125 bedside nephrology calculators plus a renal drug-dosing database, coded by a practicing transplant nephrologist.