Activated Partial Thromboplastin Time (aPTT) QC Failure Project

Submitted By: Ami Desai

Project Year: 2016

Project Team Members: Ami Desai – Clinical Laboratory Scientist, Humphrey Okeke – Hematology Supervisor

Organization/ Location: California, USA

Type of Laboratory: Clinical Laboratory

What problem were you trying to solve? aPTT QC failures

Instruments: Stago STA Compact® and Stago STA Compact Max®

Project Objective(s):

  • Identify the root cause(s) of the aPTT QC failure.

Project Design:

  • Step-by-step troubleshooting.

Project Steps:

  • Coagulation Controls
    • When the aPTT QC failed, reconstituted fresh STA® – Coag Control N Plus (Ref 00677) and STA® – Coag Control ABN Plus (Ref 00677) to identify if it was the cause of the failures.
      • This process did not resolve the failure issues.
  • aPTT Reagent
    • After determining that the Coagulation Controls were not the root cause of the QC failures, reconstituted fresh STA-PTT A 5 reagent (Ref 00595).
      • Initially, this process resolved the QC issues, then the QC failures continued.
      • With partial success, reviewed onboard times of aPTT reagent when failures occurred.
      • Per the manufacturer’s – Diagnostica Stago – recommendations, once the reagent is reconstituted with 5 mL of water it is stable for 24 hours.
      • Observed the majority of failures occurred close to the end of the 24-hour stability limit.
      • In consultation with the Hematology supervisor, adjusted aPTT reagent prep to every 12 hours to determine if there would be a net-positive effect.


  • The STA-PTT A 5 reagent was degrading before the manufacturer’s stated 24-hour onboard stability time period.
  • Adjusted the reagent onboard time to 12-hours with no further failures.
  • The Hematology Supervisor contacted Stago to make them aware of this issue.


  • In order to mitigate the increased use of the STA-PTT A 5 reagent, the volume of reagent placed on the Stago instrument prior to performing QC was changed to 2.5 mL from 5.0 mL with no adverse impact.
    • The remaining 2.5 mL of reagent is placed in the refrigerator at 2 – 8°C, which the manufacturer states will be stable for up to 7 days.
    • The remaining 2.5 mL of reagent is placed on the instrument following the initial 2.5 mL has completed 12 hours.
    • This new process reduced the amount of wasted reagent generated through repeat QC testing.


  1. STA-aPTT A 5 [Package Insert]. Asnières sur Seine Cedex, France: Diagnostica Stago S.A.S; 2016.
  2. STA-Coag Control (N+ABN) Plus [Package Insert]. Asnières sur Seine Cedex, France: Diagnostica Stago S.A.S; 2014.