INR

Sample for INR

1. This sample is just like for PTT or APTT.
2. The blood sample is taken with an ESR (sodium citrate) solution.
   • Mix blood 1.8 ml with ESR solution 0.2 ml.

Indications for INR

1. PT and PTT are advised to find the cause of unexplained bleeding or blood clot formation.
2. INR is advised to monitor the blood thinning drug’s medication, like warfarin therapy.
3. This is done for routine health screenings.
4. To evaluate whether the medical condition is improving or worsening.
5. To assess and measure the success or failure of a medication or treatment plan.
6. This measures the extrinsic pathway.

Precautions for INR and PT:

1. A high-fat diet may decrease the PT.
2. Alcohol use may increase the PT value.
3. There are certain drugs that may increase the PT value are:
   1. Barbiturates.
   2. Amonosalicylic acid.
   3. Allopurinol.
   4. Beta-lactam antibiotics.
   5. Chloramphenicol.
   6. Cephalothins.
   7. Cimetidine.
   8. Clofibrate.
   9. Alcohol.
   10. Neomycin.
4. There are certain drugs that can decrease the PT value are  following:
   1. Anabolic steroids.
   2. Digitalis.
   3.  Benadryl (Diphenhydramine).
   4. Oral contraceptives.
   5. Vitamin K.

Definition of INR

1. This is the patient’s prothrombin time (PT) ratio and the normal mean PT time raised to the power of the international sensitivity index.
2. INR is a  measure of the sensitivity of the specific tissue factor used in the test, as compared with a World Health Organization standard (normal British brain tissue factor).

Blood coagulation process and facts

1. Prothrombin (Factor II) is produced in the liver and is Vit. K dependent.
2. Vit. K deficiency leads to a decreased level of Prothrombin and gives rise to a bleeding tendency.
3. PT is used to evaluate the extrinsic pathway and common pathway.

Coagulation hemostasis mechanism

Prothrombin leads to stable clot formation

The first reaction of the body to active bleeding is blood vessel constriction.

The first response to vascular injury:

1. In a small vessel, the constriction may be enough to stop bleeding, while in large blood vessels, the hemostatic mechanism is involved.

The primary phase:

1. The primary phase of hemostasis is platelet aggregation and activation.
2. The hemostatic system forms the clot which plugs the vessel.

Secondary hemostasis: 

1. It will first activate the tissue factor and then the coagulation factors.
2. The extrinsic pathway is activated by tissue factor and factor VII, which stimulates factor X and enters the common pathway.
3. The intrinsic pathway occurs through XII, XI, IX, and VIII and enters the common pathway by activating factors X and Xa.

Prothrombin facts

INR (International normalized ratio):

1. INR is a simple ratio. There is no unit of INR.
2. This is calculated by dividing the patient’s PT by the mean of the normal range PT.
3. The international sensitivity index (ISI) is 1.3 to 1.5. The following is the formula.

Use of INR:

1. The prophylaxis  range of 2.0 to 3.0 is used to prevent:
   1. Embolism.
   2. Venous thrombosis.
   3. Pulmonary embolism.
   4. Myocardial infarction.
2. In patients with anticoagulant therapy, the INR is maintained between 2 and 3.
3. A raised range from 2.5 to 3.5 is used in the patient with mechanical heart valves.

What is a Normal INR

1. The INR test result is given as a number.
   1. INR = 1 represents equal to normal clotting time.
   2. INR = 2 represents twice the normal clotting time.
2. Normal range value =0.8 to 1.1
3. INR is used in oral anticoagulants:
   1. For prophylaxis = 1.3
   2. All other indications except cardiac = 2.0 to 3.0.
   3. In cardiac diseases = 2.5 to 3.5.

The required range of INR in various diseases :

PT values in various diseases:

Warfarin therapy is given in:

1. Deep vein thrombosis
2. Atrial fibrillation.
3. Pulmonary embolism.
4. Replacement of the artificial valves.
5. Some cases of heart failure.
6. Care during the Warfarin therapy:
   1. Teach the patient to check the PT and INR values regularly.
   2. Teach the patient to evaluate the bleeding tendency, like bruises, petechiae, and gum bleeding.
   3. The patient may have back pain.
   4. Blood will be positive in urine and stool.
   5. Teach the patient about the interaction of other medications, so they should take them with the permission of their physician.

High INR or Critical value and be Careful when  INR = >5.5

• Please, for more information, see PT and PTT.

Questions and answers: