Rosendaal method for therapeutic time in range

Rosendaal Method for % INR in range - method which INR-specific person-time is calculated by incorporating the frequency of INR measurements and their actual values, and assuming that changes between consecutive INR measurements are linear over time

Example: Patient has INR reading of 2.4 on October 1st, then reading of 3.2 on October 17th. Assuming the patient gradually moves towards a reading of 3.2 throughout the 16-day period between Oct 1st and Oct 17th, then we can estimate that the patient was within their INR therapeutic range [2 - 3] for a majority of that time period. To calculate the value

  1. calculate amount of the total shift (2.4 to 3.2 = 0.8 increase) that is within the therapeutic range (0.6 of shift is within range, [3.0 - 2.4 = 0.6])
  2. calculate percent of total shift within therapeutic range (0.6/0.8 = 75%)
  3. estimate number of days since last visit that were within range (75% x 16 days since last visit = 0.75 x 16 = 12 days within range, 4 days out of range). Percentage for that time period is 75% in range, and 12 total days in range.

To calculate overall % in range, add total days in range for each time period, and divide by total therapeutic days

Sample Patient

Visit Date
Type
INR
Days Since
INR Diff
Pred% In Range
 12/20/2005 8:29:19 AM
 Prior Visit 
3.3 
 
  
  
 1/17/2006 8:32:38 AM
 Onsite Training 
2.7 
  28
 -0.60 
 50% 
 2/7/2006 8:32:38 AM
 Prior Visit 
2.3 
  21
 -0.40 
 100% 
 3/7/2006 8:32:38 AM
 Prior Visit 
2.4 
  28
 0.10 
 100% 
 4/4/2006 3:54:57 PM
 Scheduled Visit 
2.2 
  28
 -0.20 
 100% 
 4/12/2006 10:48:08 AM
 Telephone Contact 
1.9 
  8
 -0.30 
 67% 
 4/25/2006 4:31:10 PM
 Scheduled Visit 
1.2 
  13
 -0.70 
 0% 
 5/2/2006 3:18:50 PM
 Scheduled Visit 
1.8 
  7
 0.60 
 0% 
 5/15/2006 3:51:58 PM
 Scheduled Visit 
3.9 
  13
 2.10 
 48% 
 5/22/2006 3:39:23 PM
 Scheduled Visit 
3.7 
  7
 -0.20 
 0% 
 5/30/2006 3:42:20 PM
 Scheduled Visit 
3.5 
  8
 -0.20 
 0% 
 6/14/2006 2:42:54 PM
 Scheduled Visit 
1.7 
  15
 -1.80 
 56% 
 6/23/2006 3:09:33 PM
 Scheduled Visit 
2.4 
  9
 0.70 
 57% 
 7/25/2006 2:50:16 PM
 Scheduled Visit 
2.5 
  32
 0.10 
 100% 
 8/22/2006 2:49:09 PM
 Scheduled Visit 
3.2 
  28
 0.70 
 71% 
 8/29/2006 3:07:13 PM
 Scheduled Visit 
2.5 
  7
 -0.70 
 71% 
 9/19/2006 3:03:26 PM
 Scheduled Visit 
2.3 
  21
 -0.20 
 100% 

INR In Range % (Traditional) = 47.06%
[8 visits within range out of 17 total visits]

INR In Range % (Rosendaal) = 71.05%
[194 days in therapeutic range out of 273 total therapeutic days]

Here is another way to view the calculations, if we look at just a few data points from above. Click images to enlarge.

Need more help with these calculations? Download an Excel spreadsheet >>