Calculating the Dose
Factor dosage is the number of units of factor needed to raise the person’s clotting factor to the desired level. The desired level is written as a percentage (%). It is based on the type of bleed the person is having. Your hemophilia doctor may make changes in your dosage based on how your body responds. Because the number of factor units needed is based on your weight, you should weigh yourself often and let your doctor know of any changes. Children should be weighed even more often than adults because as they grow the dosage they need will change. Some people figure the factor dosage based on the metric system weight. One kilogram equals 2.2 pounds.
The number of units in a bottle of factor is shown on the label. One unit of factor is the amount of factor activity found in 1 cc (or 1 ml) of fresh plasma. The number of units a person needs for treatment will rarely come out as an even number of bottles. The dosage does not have to be exact. There is no problem if the amount mixed is a little more or less than the computed dosage. If you use recombinant factor concentrate, you may have to use a higher dose. Talk to your doctor.
This section explains how to calculate the dosage for factor VIII and factor IX. First we show you how to do the math yourself. At the bottom of the page is an Automatic Dosage Calculator. You can enter your weight in either pounds or kilograms. Type the desired percentage increase of factor in the “Factor Level” box. For example, to raise the level of factor in the blood to 40%, enter 40 in the Factor Level box.
How to Calculate Dosage for Hemophilia A (Factor VIII)
The doctor may want to adjust the dosage depending on the patient’s severity level and where he is bleeding.
1. Take the patient’s present weight in pounds.
2. Divide that weight by 4.4 (a calculator may help).
3. Multiply that number by the factor level to be reached.
4. The result is the required units of factor.
Formula: weight ÷ 4.4 × factor level desired = number of factor VIII units needed
Example: A man weighing 120 pounds needs to raise his factor level to 40%. 120 lbs ÷ 4.4 × 40 = 1091 units of factor. If the bottles of factor on hand have 600 units each, he should receive two bottles. NOTE: It is difficult to get the exact amount needed. It is always better to infuse more units than fewer units.
You should use all of the factor in the bottle. A person with hemophilia A will not be harmed if he receives a little more factor VIII than is called for; it just costs more.
If, after 24 to 36 hours, you are still bleeding, you may need to take factor again. If you still have symptoms of the bleed after taking factor a second time, call your doctor.
How to Calculate Dosage for Hemophilia B (Factor IX)
The doctor may want to adjust the dosage depending on the patient’s severity level and where he is bleeding.
1. Take the patient’s present weight in pounds.
2. Divide that weight by 2.2 (a calculator may help).
3. Multiply that number by the factor level to be reached.
4. The result is the required units of factor.
Formula: weight ÷ 2.2 × factor level desired = number of factor IX units needed
Example: A man weighing 120 pounds needs to raise his factor level to 40%. 120 lbs ÷ 2.2 × 40 = 2182 units of factor. If the bottles of factor on hand have 600 units each, he should receive four bottles.
NOTE: With factor IX, it is important not to give more than the maximum dosage prescribed.
If, after 36 to 48 hours, you are still bleeding, you may need to take factor again. If you still have symptoms of the bleed after taking factor a second time, call your doctor.
Automatic Dosage Calculator