The INR (International Normalized Ratio) value is a laboratory parameter that describes blood clotting.
To determine the INR value, blood tests measure the time it takes for the blood to clot (called the thromboplastin time or TPZ).
Along with the determination of the Quick value, the INR is the second way of expressing the TPZ. Unlike the Quick value, this is a standardized value (i.e., the value is independent of method and laboratory). It is therefore safer to use and internationally comparable.
The procedure
Material required
- Citrate blood
Preparation of the patient
- Not known
Disruptive factors
- Long venous congestion
- Severe aspiration during blood sampling
- Insufficient filling of the tube (= incorrect citrate-plasma ratio).
- Too low centrifugation
- Medication:
- Antibiotics:
- Cephalosporins
- Penicillin
- Sulfonamides
- Anticonvulsants
- Acetylsalicylic acid (ASA)
- Barbiturates
- Heparin
- Antibiotics:
INR
| Value | Meaning |
| 0,9-1,15 | Normal blood clotting |
| 2,0-4,5 | Therapeutic range in treatment with anticoagulants (anticoagulant drugs). |
Indications
- Therapy with vitamin K antagonists (VKA; Marcumar, warfarin).
- Differential diagnosis of hemorrhagic diathesis (coagulation disorders with increased bleeding tendency).
- Preoperative screening for coagulopathy (disorder of blood coagulation).
- Progression assessment of hepatopathies (liver diseases)/liver cell functional performance (synthesis performance of the liver) in severe liver parenchymal disease (disease of the part of the liver containing liver cells (hepatocytes)).
- Suspected vitamin K deficiency
Interpretation
The therapeutic range is targeted for the following conditions:
- Cardiac arrhythmias (atrial fibrillation, VHF).
- In mechanical valve replacement (here the INR is raised to values of 3.0 – 4.5 the furthest); in biological valve replacement (INR: 2.0 – 3.0).
- Recurrent deep vein thrombosis, pulmonary embolism.
- Zust. n. leg vein thrombosis (formation of a blood clot with occlusion of a vessel).
- Zust. n. pulmonary embolism (detachment of a blood clot from the leg with occlusion of pulmonary vessels).
- Zust. n. Myocardial infarction (heart attack).
- Zust. n. transient ischemic attack (TIA).
- Postoperative prophylaxis of deep venous thrombosis.
- Prolonged immobilization after hip surgery and femur fracture surgeries (fracture of the femur).
Causes of elevated INR:
- Anticoagulant therapy (therapy to inhibit blood clotting).
- Direct oral anticoagulants (NOAK or DOAK)* .
- Dysfibrinogenemia (decrease in clot-active fibrinogen).
- Hepatopathies/liver diseases (see liver parameters).
- Lupus anticoagulant (antiphospholipid antibody).
- Neonates (immature hemostasis system).
- Prothrombin complex deficiency
- Consumptive coagulopathy (consumption of clotting factors and platelets/platelets, which can lead to a bleeding tendency).
- Vitamin K deficiency
* Note: Measurement of INR is not suitable under new or even direct oral anticoagulants (NOAK or DOAK, respectively) to provide information about anticoagulation. In patients with NNOAK, routine INR testing should be avoided.