Laboratory Investigations

Cork Kerry Laboratory Guidelines for Hospitals and Primary Care



The indications for clotting screen (APTT / INR):

  • Haemorrhage unrelated to trauma
  • History of a known or suspected bleeding disorder
  • Known or suspected liver disease
  • Paracetamol OD with a delay in seeking medical advice
  • After massive rapid transfusion
  • Suspected disseminated intravascular coagulation
  • Stroke patient

Draw order

Draw Order CUH
Order Colour Contents Assay Notes
1 Blue top Citrate Coagulation Studies: INR, D-Dimer. Fill to arrow line. Inadequately filled tubes cannot be used
2 Red top Coagulant General Biochemistry, Serology, Immunology & Virology tests, Lipid profile, Cold Agglutinins, Viral Antibody & Antigen Testing, Antibiotic assays,Hormone studies, Anti Cardiolipin AB., B12 Folate, Ferritin, RA, Intrinsic Factor AB., Endocrinology tests. Lipid Profile requires a fasting sample
3 Green top Heparin Chromosomes, Lead levels, Amino acids.  
4 Purple top EDTA FBC, HBA1C, Haemoglobin Electrophoresis, Malaria Parasites, Sickle cell, Abnormal Hb Screen, Reticulocyte Count, Coombs Test, Cyclosporins, Tacrolimus, Immunophenotyping, Silrolimus, ESR, PTH, DNA analysis.  
5 Pink top EDTA Crossmatch, Group & Alb. Handwritten details only. No addressograph
6 White tops Oxalate Blood sugar Glucose levels, Glucose Tolerance Tests, Lactate. State time on sample & state whether sample is fasting or random
7 Yellow top ACD-As HLA typing  

Troponin

With the TnI system (as in use in CUH):

  • 34ng/L is the upper normal limit in men
  • 16ng/L is the upper normal limit in women
  • The lower limit of detection (LOD) is taken as 5ng/L
  • As the tests are becoming more sensitive, more false positives may be recorded.
  • The diagnosis of AMI requires:
    • A ↑ and/or ↓ of biomarkers (e.g. cTnI) with at least one value above the 34/16 4ng/L PLUS
    • Symptoms of ischaemia or appropriate ECG changes and/or imaging evidence of new wall motion abnormality.
  • Troponin is only one variable. Risk stratification requires clinical assessment and /or scoring e.g. HEART.
  • Two measurements of TnI are required (at presentation and after 3 hours) unless max pain (and no longer in pain) was > 3 hours ago (one <LOD will suffice in low risk patients).
  • AMI = rise above normal and Δ > 50% over that same period.
  • Δ 20-100% within a 3 hr period requires further testing.
  • Δ <20% within 3 hrs is not consistent with an acute event.
  • Dx of AMI post PCI or CABG requires a three fold increase in TnI.

Thrombophilia

Thrombophila screening should not be done in ED during the acute phase after a clot.

The below only refers to OPD Mx/Follow up, not ED.

  • Inherited abnormalities which predispose to thrombosis are prevalent in the Irish Population.
  • These can be due to deficiencies or abnormalities of natural inhibitor proteins of the coagulation system.
  • These inhibitors exist to control the rate of formation of a blood clot.
  • A second cause of inherited thrombosis is deficiency of proteins in the fibrinolytic system, these proteins break down blood clots once they are formed.
  • Deficiencies of the fibrinolytic system are very rare and analysis is only carried out following assessment by haematology medical staff.

Protein C.

Protein C is part of the anticoagulant regulatory mechanism. It is converted to activated protein C (APC) by thrombin in the presence of thrombomodulin. APC inactivates activated factors V and VIII. Protein C deficiency has been shown to be a risk factor for thrombosis.

Antithrombin

Antithrombin (AT) is a major inhibitor of blood coagulation and is essential for effective heparin therapy. AT inhibits the coagulation proteases including II a, X a , IX a and XI a. AT deficiency is associated with a high risk of thrombotic disorders.

Free Protein S

Protein S is a vitamin K dependent cofactor for the anticoagulant activity of activated protein C (APC). Two forms of protein S are present in plasma : free protein S (40%) and protein S linked to the C4b-binding protein (60%). Only the free form has functional cofactor activity. Protein S deficiency may be hereditary or acquired – as in normal pregnancy. It has been associated with a high risk of developing venous thromboembolism especially in young people. As only the free form of Protein S has the cofactor activity it is only this form that is measured. Measurement of Protein S in pregnancy is rarely useful.

APC Resistance Assay

Protein C is a naturally occurring inhibitor of blood coagulation, acting on activated factor V and VIII. When patient’s plasma does not produce the appropriate anticoagulant response to activated protein C (APC) in the laboratory, this is termed APC resistance. APCR is caused by the VQ506 gene mutation which produces factor V Leiden, a factor V molecule which is resistant to cleavage by activated protein C and therefore prothrombotic.

Factor V Leiden mutation

The identification of Factor V Leiden mutation is carried out using PCR technology. This method is used to identify the genotype of the abnormality. PCR testing is carried out on all samples that have a reduced APCR or have a family history of factor V Leiden.

Prothrombin gene mutation (G-20210-A).

The mutation in the factor II gene (G-20210-A) is in the untranslated portion at start of the gene and is probably part of the the regulatory system for the gene. People carrying the mutation have higher levels of factor II than normal and the increased risk of thrombosis is thought to be a function of this.

Lupus anticoagulant (LA)

LA is an acquired abnormality which is associated with an increased risk of venous thrombosis. LA is named for its association with SLE. A lupus anticoagulant is an anti-phospholipid antibody.

Lupus anticoagulant (LA) results in prolongation of coagulation tests such as the APTT, dependent on phospholipid. Dilute Russell Viper Venom Time (DRVVT) is used to detect the presence of these inhibitors. LA is associated with a range of autoimmune disorders, infections and treatment with some drugs.

The presence of LA may be suggested by:

  1. Unexplained prolongation of APTT
  2. Recurrent early foetal loss thought to be due to placental infarct
  3. Unexplained thrombotic tendency
  4. Thrombocytopenia in association with thrombosis

Who Should have Thrombophilia Screening?

Thrombophilia screening is expensive (€200) and time consuming and it is therefore important that it is targeted at the correctly. At risk patients include:

  1. Known FHx of any of the inherited thrombophilia factors.
  2. FHx of proven venous thromboembolism. (more than two symptomatic members).
  3. Patients who have developed a thrombosis with no obvious precipitating cause or at age < 40.
  4. Hx recurrent miscarriages, pre-eclampsia, IUGR and stillbirth should be screened for the lupus anticoagulant.
  5. Neonates and children with purpura fulminans should be screened urgently.

What tests should be done?

  • Protein C
  • Protein S
  • Antithrombin
  • APCR and Factor V Leiden genetic analysis
  • Protein gene mutation (Prothrombin 20210)
  • Lupus anticoagulant and B2 glycoprotein 1

Thrombophila screening should not be done during the acute phase after the patient presents with a clot.

Patients should be tested after the acute event and after any anticoagulation therapy (1 month post Warfarin therapy - Prot C and S are vit K dependant).

Patients on LMWH can be tested.


Blood Ketone Sampling

Could all Paediatric patients who require phlebotomy for hypoglycaemia or DKA please have an extra 0.5ml Lithium Heparin (orange top) sample sent to Biochemistry please. The lab form should be marked - “Point of Care Blood Ketone Testing. FAO Mary Stapleton.”

Please also insert patient’s Name and MRN into the “Blood Ketones” folder on the desktop of the Paeds computer for our records.

This is part of a laboratory-led quality assurance study with a view to ultimately acquiring Ketone Strips for CUH. Thank you.



Content by Dr Íomhar O' Sullivan from the Cork Kerry Laboratory Guidelines for Hospitals and Primary Care