Another concern about having your blood drawn on Friday, but the lab work apparently done on Monday is that improper storage of the blood could also be suspect for getting erroneous values. If I HAD to have a blood draw, I'd want my results done before the blood had much time for a lab to mishandle. I'm a strong advocate for self testing, and I hope you can convince the NHS of your need to do self testing.
I don't use a 7 day pill box - but I take the same dose every night (at around 11 PM), so it's pretty hard to screw up my dosage (although, theoretically, I could forget to take my dose, but don't think it's happened recently). As a self-tester, I created my own spreadsheet - both so I can keep track of many factors that may have had an effect on my INR and also so I can show a doctor that I'm regularly recording the INR and am able to effectively manage it. The fields include Date and Time of test, INR, Prothrombin time (which isn't particularly relevant and varies from meter to meter and batch of strips to batch of strips), weekly dosage, and any comments that may be relevant. These comments include such things as any dietary or activity changes, any medications started or stopped, any Over the counter medications I've started or stopped, any recent illnesses, etc. Although I'm sure that there are probably printed INR diaries available, maintaining the information on a spreadsheet - and fairly regularly copying it - provides a potentially useful ongoing record of INR and overall condition.
I don't use a 7 day pill box - but I take the same dose every night (at around 11 PM), so it's pretty hard to screw up my dosage (although, theoretically, I could forget to take my dose, but don't think it's happened recently). As a self-tester, I created my own spreadsheet - both so I can keep track of many factors that may have had an effect on my INR and also so I can show a doctor that I'm regularly recording the INR and am able to effectively manage it. The fields include Date and Time of test, INR, Prothrombin time (which isn't particularly relevant and varies from meter to meter and batch of strips to batch of strips), weekly dosage, and any comments that may be relevant. These comments include such things as any dietary or activity changes, any medications started or stopped, any Over the counter medications I've started or stopped, any recent illnesses, etc. Although I'm sure that there are probably printed INR diaries available, maintaining the information on a spreadsheet - and fairly regularly copying it - provides a potentially useful ongoing record of INR and overall condition.