Tools to support a clinical aTTP diagnosis

PLASMIC and French scores can be used to predict ADAMTS13 deficiency1

PLASMIC and French scores are based on laboratory parameters such as platelet count and creatinine level.2

Plasmic Score1

Parameter

Score

Platelet count <30 × 109/L +1
Serum creatinine level <2.0 mg/dL +1
Evidence of hemolysis*:
Indirect bilirubin >2.0 mg/dL
or Reticulocyte count >2.5%
or Undetectable haptoglobin
+1
No active cancer in previous year* +1
No history of solid organ or stem cell transplantation* +1
INR <1.5* +1
MCV <90 fL (<9.0 × 10-14/L) +1

Likelihood of severe
ADAMTS13 deficiency

Low risk
0 to 4: 0% to 4%
Intermediate risk
5: 5% to 24%
High risk
6 to 7: 62% to 82%

Validation of the PLASMIC score1

Derivation validation cohort
(n=200)
Internal validation cohort
(n=150)
External validation cohort
(n=146)
0-4 0/84 (0%) 0/89 (0%) 2/47 (4%)
5 2/44 (5%) 3/32 (9%) 6/25 (24%)
6-7 58/72 (81%) 18/29 (62%) 61/74 (82%)
Derivation validation cohort
(n=200)
0-4 0/84 (0%)
5 2/44 (5%)
6-7 58/72 (81%)
Internal validation cohort
(n=150)
0-4 0/89 (0%)
5 3/32 (9%)
6-7 18/29 (62%)
External validation cohort
(n=146)
0-4 2/47 (4%)
5 6/25 (24%)
6-7 61/74 (82%)

These data refer to the number of individuals with ADAMTS13 activity ≤10% and to the total number of individuals with this score.3

The PLASMIC score can predict severe ADAMTS13 activity as criteria for identifying a patient with probable TTP, such as3 :

  • Absence of clinical conditions that can justify microangiopathy (eg, cancer, transplant, DIC)
  • Presence of severe thrombocytopenia (<30 × 109/L)
  • Mild or no renal insufficiency (creatinine)

This score does not replace a TTP diagnosis, which is based on the activity of ADAMTS13 and anti-ADAMTS13 antibodies.2

French Score1

Parameter

Score

Platelet count <30 × 109/L +1
Serum creatinine level <2.25 mg/dL +1

Prediction of severe ADAMTS13 deficiency (activity <10%) based on score

0: 2%
1: 70%
2: 94%

The PLASMIC and French scores can be a valid help in cases of 
diagnostic suspicion to quickly identify if a patient needs 
emergency treatment2

ADAMTS13=a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 13; DIC=disseminated intravascular coagulation; INR=international normalized ratio; MCV=mean corpuscular value.
Each item is associated with one point (+1).
*The French score considers patients with a thrombotic microangiopathy syndrome (which includes hemolysis with schistocytes in the definition) and assumes that there is no history of or clinical evidence for associated cancer, transplantation, or disseminated intravascular coagulopathy, so these items are intrinsic to the score.1
MCV was not incorporated into the French score.1
Results correspond to those of the derivation cohort and those of a validation by (French score) the bootstrap resampling technique (internal validation) or (PLASMIC score) different samples of patients from the same institution (internal validation) or from a different institution(external validation).1
References:
  1. Coppo P, Cuker A, George JN. Thrombotic thrombocytopenic purpura: toward targeted therapy and precision medicine. Res Pract Thromb Haemost. 2019;3(1):26-37. doi:10.1002/rth2.12160
  2. Zheng XL, Vesely SK, Cataland SR, et al. ISTH guidelines for the diagnosis of thrombotic thrombocytopenic purpura. J Thromb Haemost. 2020;18(10):2486-2495. doi:10.1111/jth.15006
  3. Bendapudi PK, Hurwitz S, Fry A, 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. doi:10.1016/S2352-3026(17)30026-1