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Reference Range:

Frimley Park Hospital APTT 23-35 secs HEP (I.V. heparin therapy APTT) 50-75secs. Royal Surrey County Hospital APTT 0.9-1.15 Unfractionated heparin – 1.5 – 2.5

Turnaround Time:

Urgent 1hr: Non urgent 2hrs


If patients are on anticoagulants the type of anticoagulant should be stated clearly in the request.
All relevant clinical details must be provided with the request.


The Activated Partial Thromboplastin Time (APTT) assay is a universally accepted screening procedure used to detect abnormalities in the intrinsic coagulation system. It can be used to detect deficiencies of Factors II, V, VIII, IX, X, XI and XII. In addition, it can be used to detect lupus anticoagulants and is recommended when monitoring unfractionated heparin therapy since it is sensitive to the presence of heparin


For APTT, 9 volumes of blood added to 1 volume of sodium citrate solution. This ratio of anticoagulant to blood is critical as osmotic effects and changes in free calcium ion concentrations affect the coagulation results. Obtaining blood from an in-dwelling line or catheter is a potential source of error due to likely heaprin contamination, therefore sampling from those is unacceptable.

Vessels and Containers:

1x4.5 Sodium Citrate (Blue top)

Sample Requirements:

1x4.5 Sodium Citrate (Blue top) Underfilled samples will invalidate results
Haemolysis will invalidate results
All medication must be written on the request form
APTT samples must be tested within 6 hours


Bottles should be correctly filled and the sample should not be haemolysed or clotted. The results of samples that are icteric or lipaemic should be interpreted with caution.

How result is reported:

Results are reported as per reference range, if the sample quality is acceptable.
If the sample quality is not acceptable (due to overfilled or underfilled or haemolysed or clotted samples) then the test request will be cancelled and the reason for cancellation is reported.

Important Information:

Citrate Samples which are more than 4hrs old will not be processed by the laboratory.

Transportation and Handling:

Samples which are to be transported by hand or local transport should be dispatched in clearly sealed individual plastic bags within 4 hours of collection.
If it is sent from longer distances, the person sending the specimen must ensure that the appropriate specimen container is used and samples must be spun (following protocol)and plasma should be separated and frozen to -70*C prior to transport. Contact Laboratory if advice required

Time limits for requesting additional examinations:

All add on tests should be requested within 4hrs from the time sample taken.