A Coagulation Screen comprises:
- Prothrombin Time (PT)
- Prothrombin Time Ratio (PTR)
- Activated Partial Thromboplastin Time (APTT)
- Activated Partial Thromboplastin Time Ratio (APTTR)
- Fibrinogen (Clauss)
The Coagulation Screen is a combination of tests designed to provide rapid information and allows an initial broad categorisation of haemostatic function. It is the basis from which all specialist coagulation tests are reflexed.
The Coagulation screen is used in many scenarios including as a pre-operative screen to assess bleeding risk, monitor bleeding conditions and some therapies, and also to assess patients demonstrating a bleeding/bruising history or a thrombosis history or that have a family history of bleeding/bruising. It must be noted that these parameters are helpful but do not detect all haemostatic abnormities, thus clinical history is still of the utmost importance to aid in the diagnosis of a condition.
Individually raised PT and APTT results without cause, or where it is deemed clinically appropriate (i.e. bleeding, bruising or thrombosis), should always be further investigated.
If both PT and APTT are prolonged this can be an indication of other conditions and deficiencies including deficiencies in the common pathway, as well as multiple deficiencies as demonstrated in liver disease or Disseminated Intravascular Coagulation (DIC) or sepsis.
Current laboratory (adult, M/F) normal ranges are as follows:
- PT: 12.0 – 14.8 seconds
- PTR: 0.9 – 1.1
- APTT: 27.0 – 41.0 seconds
- APTTR: 0.8 – 1.2
- Fibrinogen: 1.9 – 8.0 g/L
The volume of blood in coagulation samples must lie within the volume range as indicated by the size of the black fill arrow present on tubes. Volumes above or below the arrow will result in sample rejection to ensure validity of results.
- 1 blue top (sodium citrate) sample.
- All coagulation tubes must be adequately filled (see above).
- All coagulation tubes must be mixed several times by gentle inversion immediately after venepuncture. Mixing the sample with the anticoagulant stops the sample clotting within the tube.
Limitations and restrictions
- It is not possible to provide results on clotted, insufficient, or haemolysed samples. These will be rejected with the appropriate comment.
- Sample tubes that have expired cannot be accepted.
- Samples will be rejected if received more than 8 hours after venepuncture.
- Urgent samples: 1 hour and 15 minutes
- Routine samples: 4 hours
- Coagulation Lab, James Cook University Hospital, Marton Road, TS4 3BW
- Coagulation Lab, Friarage Hospital, Northallerton, DL6 1JG
In some instances of low fibrinogen samples may be referred for genetic analysis to Queens Medical Centre, Derby Road, Lenton, Nottingham, NG7 2UH