Partial Thromboplastin Time (PTT), Activated

Also known as: Activated Partial Thromboplastin Time (aPTT)

Clinical Use

Use

The aPTT is sensitive to deficiency or inhibition of factors in the intrinsic pathway. These include the contact factors; high molecular weight kininogen (HMWK), prekallikrein, and factor XII along with procoagulant factors XI, IX, VIII. The aPTT is less sensitive to deficiencies of X, V, prothrombin, and fibrinogen.1 Nonspecific, lupus-type anticoagulants can also extend the aPTT, but the more sensitive aPTT-LA test should be used to screen for this condition.

Special Instructions

Not provided.

Limitations

The aPTT test has limitations for identifying lupus anticoagulants, where a more sensitive aPTT-LA test may be preferred. Individual factor deficiencies may not significantly extend the aPTT unless levels fall below 15% to 45%, depending on the factor. Multiple factor deficiencies can cause an extended aPTT, but the test is more sensitive to intrinsic pathway factor deficiencies than common pathway deficiencies. Conditions that elevate factor VIII, such as acute phase reactions, can normalize an extended aPTT. Several factors such as aging, obesity, liver or renal disease, and variations in heparin response can complicate its use in heparin therapy monitoring. The test should not be used for monitoring low molecular weight heparin or danaparoid.

Test Details

Methodology

Other

Biomarkers

Contact Pathway Coagulation Factors

Other

Clotting Time

Concentration / Level • Quantitative (Continuous) (e.g., copies/mL, % expression)

LOINC Codes

Order Codes

14979-9 - aPTT PPP

Result Codes

14979-9 - aPTT PPP

Result Turnaround Time

1 day

Specimen

Whole Blood

Volume

4.5 mL, 2.7 mL, 1.8 mL

Minimum Volume

90% of full draw

Container

Blue-top (sodium citrate) tube

Collection Instructions

Collect blood in a 3.2% buffered sodium citrate blue-top tube. Fill tubes to completion to ensure proper blood-to-anticoagulant ratio. Mix by gentle inversion at least six times. If using a butterfly collection set, draw a discard tube first.

Patient Preparation

Draw specimen one hour before the next dose of heparin if given by intermittent injection. Do not draw from an arm with a heparin lock or heparinized catheter.

Storage Instructions

Specimens stable at room temperature for 24 hours; if not tested within this time, centrifuge and freeze plasma. For patients on heparin, if not tested within one hour, submit frozen plasma.