Are shortened aPTT values always to be attributed only to preanalytical problems?

Area of Science:

• Clinical Chemistry
• Hematology
• Coagulation Diagnostics

Background:

• Shortened activated partial thromboplastin time (aPTT) can stem from various preanalytical conditions.
• Coagulation Factor VIII (FVIII) is integral to the intrinsic pathway measured by aPTT.
• The study investigates the link between elevated FVIII activity and shortened aPTT.

Purpose of the Study:

• To examine the association between elevated FVIII activity and shortened aPTT.
• To explore the influence of inflammation on routine laboratory parameters, including aPTT and FVIII.
• To differentiate preanalytical causes from biological factors contributing to shortened aPTT.

Main Methods:

• Inclusion of 40 patients with aPTT below the lower reference limit (<23.0 s).
• Collection of samples from 25 healthy volunteers as a control group.
• Measurement of white blood cell count, C-reactive protein, aPTT, and FVIII values in both groups.

Main Results:

• Only 5% of patient samples with shortened aPTT were clotted; the rest were clot-free.
• 26 out of 38 evaluable patients (68%) exhibited elevated FVIII activity (>150%), with a median of 194%.
• Multiple regression analysis identified FVIII activity as the sole independent predictor of aPTT values (p=0.001).

Conclusions:

• Shortened aPTT is infrequently caused by preanalytical problems.
• Elevated FVIII activity is a significant cause of shortened aPTT.
• This elevation impacts aPTT regardless of the inflammatory state or presence of inflammatory markers.