Coagulation Screens

Interpretation of coagulation screens

Effective haemostasis requires correct functioning of the vessel endometrium, platelets and coagulation proteins. Coagulation screens offer in vivo testing of the coagulation proteins only.

The pathways may be affected by several in vivo & in vitro factors eg underfilling of tubes, incorrect storage and lupus anticoagulants. It is therefore important to interpret screens in the light of the patient’s clinical status.

Pre operative screens

Coagulation screens on pre operative elective patients are performed to identify any undiagnosed bleeding tendency. In the elective, non-hospitalised patient this will be an undiagnosed inherited bleeding disorder e.g. von Willebrand’s disease. In this group of patients it is therefore acceptable to use the results of any previous coagulation screen without the need to repeat the screen within the pre operative period providing there is no new history of bleeding. Hospitalised or unwell patients should have a recent coagulation screen performed.

Laboratory normal ranges

Current laboratory (adult, M/F) normal ranges are as follows:

Test
Sample requirements
Reference ranges
Reference laboratory perform confirmatory testing
Associated clinical guideline
Prothrombin time (PT) 1 citrate sample 12.7-15.0 seconds*
Activated Partial Thromboplastin Time (APTT) 1 citrate sample 27.0-42.0 seconds*
Fibrinogen (Derived/Clauss) 1 citrate sample 1.9-8.0g/L
Thrombin Time 1 citrate sample 14.5-18.5 seconds*
Reptilase 1 citrate sample 15.7-20.2 seconds*
D-dimer cut-off for VTE exclusion in conjunction with a Low Clinical Probability Score (CPS) 1 citrate sample
MUST be received into Lab within 4 hours of venepuncture
< 0.50 µg/mL (FEU)
Anti-Xa assay 2 citrate samples (included in final report) Royal Victoria Infirmary
Lupus Anticoagulant 2 citrate samples, MUST be received into Lab within 4 hours of venepuncture (part of thrombophilia screen but also performed as single test) < 1.2 (ratio) Special Haematology Laboratory, Sheffield
and

Sheffield Molecular Genetics Service, Sheffield Children’s NHS Trust
CG22 – Thrombophilia testing guideline
Antithrombin III (part of thrombophilia screen) 80 – 129%
Protein C (part of thrombophilia screen) 72–156%
Protein S (part of thrombophilia screen) Male: 70-148%
Female: 56-145%
Thrombophilia Screen 5 citrate samples and 1 SST , MUST be received into Lab within 1 hour of venepuncture
Factor II Assay 3 citrate samples, MUST be received into Lab within 1 hour of venepuncture 73 – 121% Royal Victoria Infirmary
Factor V Assay 66 – 141%
Factor VII Assay 51 – 151%
Factor VIII Assay 56 – 174%
Factor IX Assay 62 – 138%
Factor X Assay 67 – 139%
Factor XI Assay 58 – 157%
Factor XII Assay 65 – 155%
Factor XIII Assay 50 – 150%
von Willebrands Screen includes:
RICOF:
vW Antigen:
3 citrate samples, 1 EDTA and 1 Group and Save sample.
These MUST be received into Lab within 1 hour of venepuncture
50 – 150%
50 – 160%
Royal Victoria Infirmary
HIT Screens in conjunction with an Intermediate or High pre-test probability score (4T) 1 plain red top (included in final report) Freeman Hospital CG18 – Heparin induced thrombocytopaenia guideline
Factor V Leiden Mutation Screen
Prothrombin Gene
Mutation Screen
1 citrate sample (part of thrombophilia screen but also performed as single test) Royal Victoria Infirmary CG22 – Thrombophilia testing guideline
Warfarin Quantification
(Haematologist request only)
2 plain red top tubes (included in final report) Cardiff Toxicology Laboratories
ADAMTS 13
(Haematologist request only)
2 citrate samples, MUST be received in Lab within ONE hour of venepuncture. (included in final report) Freeman Hospital
Antithrombin Genetics
Protein C Genetics
Protein S Genetics
(Haematologist request only)
3 EDTA samples (included in final report) Sheffield Molecular Genetics Service, Sheffield Children’s NHS Trust
Fibrinogen ELISA
(Haematologist request only)
3 citrate samples (included in final report) Special Haematology Laboratory, Sheffield
Fibrinogen genetics
(Haematologist request only)
3 EDTA samples (included in final report) Queens Medical Centre, Nottingham
HIT ELISA
(Haematologist request only)
1 plain red top (included in final report) Freeman Hospital
Inhibitor Screen
(Haematologist request only)
2 citrate samples (included in final report) Royal Victoria Infirmary
Lupus Mix
(Haematologist request only)
2 citrate samples (included in final report) Special Haematology Laboratory, Sheffield
MTHFR
(Haematologist consultant only request)
3 EDTA samples (included in final report) Sheffield Molecular Genetics Service, Sheffield Children’s NHS Trust
Platelet Aggregation studies
(Haematologist request only)
5 citrate samples
MUST pre-arranged with the Lab
(included in final report) Royal Victoria Infirmary
Protein C, Protein S or Antithrombin Confirmation
(For confirmation of previous abnormal result)
3 citrate samples (included in final report) Sheffield Children’s NHS Trust

* May be slight batch variation – current ranges always available on APEX.

All Coagulation specialist test results once approved by a haematologist will include a clinical comment to aid with diagnosis.

Key Factors known to affect test performance or interpretation

  • 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.
  • Samples will be rejected if received more than 8 hours after they are taken for routine clotting, more than 4 hours for D-dimers and more than 1 hour for specialist tests.
  • All coagulation samples must be kept at room temperature.
  • It is not possible to provide accurate results on clotted, insufficient, lipaemic or haemolysed samples. These will be rejected with the appropriate comment.
  • Small samples are difficult to process and will only be accepted for small children.
  • All specialist tests must include all relevant clinical details otherwise these will not be processed.

Turnaround times for coagulation

The published times are from time of receipt in the laboratory.

Routine coagulation assays
Clotting screen 4 hours
INR 4 hours
D dimer 4 hours
Lupus anticoagulant 1 week
Thrombophilia screen (non specialist) 3 weeks
Thrombophilia screen including molecular screening 4 weeks
Von Willebrands screen 4 weeks
Factor assays 1 week
Urgent coagulation assays
Clotting screen 45 minutes
INR 45 minutes
D-dimer 45 minutes

Normal working hours turnaround times for urgent specialist tests

Urgent requests for more specialist test MUST be discussed with the haematologist on call

Factor assays 2 hours
Lupus anticoagulant 2 hours
Obstetric thrombophilia screen 1 week

Referral Laboratories

Sheffield Molecular Genetics Service, Sheffield Children’s NHS Trust, Western Bank, Sheffield, S10 2TH
Coagulation Laboratory, Path Labs, Royal Victoria Infirmary, Queen Victoria Road, Newcastle-Upon-Tyne NE1 4LP
Special Haematology Laboratory, Floor H, Glossop Road, Sheffield, South Yorkshire, S10 2JF
Coagulation Laboratory, Freeman Hospital, Freeman Road, High Heaton, Newcastle-Upon-Tyne, NE7 7DN
Cardiff Toxicology Laboratories, Toxicology Laboratory, The Academic Centre, Penarth, CF64 2XX
Molecular Diagnostics, University Hospital, Queens Medical Centre, Nottingham, N97 2UH