Use of the Platelet Count and Prothrombin Time to Separate TTP-HUS from DIC

 

Parameters:

(1) platelet count per µL

(2) prothrombin time (PT) in seconds

(3) upper limit of the reference range for the prothrombin time (ULN) in seconds

Parameter	Finding	Points
platelet count	>= 20,000 per µL	0
	< 20,000 per µL	1
PT - ULN	< 5 seconds	1
	>= 5 seconds	0

 

total score =

= (points for platelet count) + (points for PT minus ULN)

 

Interpretation:

• minimum score: 0

• maximum score: 2

• A score of 2 was 52% sensitive for TTP-HUS and 92% specific.

• A platelet count < 20,000 per µL was 59% sensitive and 86% specific for TTP-HUS.

• A PT-ULN difference of < 5 seconds was 93% sensitive and 57% specific.

• ADAMTS13 testing can help to confirm the diagnosis of TTP-HUS but may not be readily available. Most patients with TTP-HUS will have an ADAMTS13 activity of < 5%.

 

Limitations:

• Almost half of the patients with TTP-HUS would not score 2 points.

• The prevalence of TTP-HUS vs DIC will impact the diagnostic performance of the criteria.