Glossary

These are definitions of terminology, not clinical guidance. No target range, dose ceiling or threshold appears anywhere on this page: those belong to the protocol your service has written and to the prescriber who set them.

Anticoagulation service

The pharmacy, clinic or hospital team that runs the follow-up: obtaining the INR, applying the prescriber’s protocol, setting the next dose and the next appointment, and keeping the record. In some countries this is a dedicated service; in others it sits with the community pharmacist.

Audit trail

The record of who entered or changed what, and when. In anticoagulant follow-up it is what lets a dose given months ago be traced back to the result and the protocol it came from.

Dosing calendar

The day-by-day schedule of tablets a patient is asked to take until their next test, usually printed at the visit. It is the document a later question is checked against.

INR

The International Normalized Ratio: a standardised way of reporting how long a blood sample takes to clot. Standardised so that a result from one laboratory means the same as a result from another, whichever reagent each of them used.

International Sensitivity Index (ISI)

The value a manufacturer assigns to a batch of reagent, placing it against the international reference. It is what converts a prothrombin time into an INR, and the reason two laboratories can report comparable results at all.

Oral anticoagulation therapy

Ongoing treatment with an oral anticoagulant, together with the monitoring and dose adjustment that goes with it. In this context it always means a vitamin K antagonist, since that is the class INR monitoring exists for.

Point-of-care INR testing

An INR measured on a handheld meter from a fingerstick sample, rather than sent to a laboratory from a venous draw. The result arrives during the visit, which is what makes the dose and the next appointment decidable while the patient is still there.

Proportion of tests in range

The simpler way of calculating time in therapeutic range: count the results that fell inside the range and divide by the results taken. It answers a different question from Rosendaal — how many tests, not how many days — and the two can disagree substantially for the same patient.

Prothrombin time (PT)

The raw clotting time a laboratory measures. On its own it shifts with the reagent used, which is why results are reported as an INR rather than as a bare number of seconds.

Recall interval

The time between one INR test and the next for a given patient, set by the prescriber’s protocol. Recording it is what turns a series of visits into a follow-up that can be shown to have happened.

Rosendaal linear interpolation

A way of calculating time in therapeutic range that treats the INR as having moved at a constant rate from one test to the next, and credits each day in between accordingly. It answers how much of the patient’s time was in range, which is why most published series use it.

Self-monitoring

A patient measuring their own INR at home on a handheld meter and reporting the result to the service that manages their dose. Distinct from self-management, where the patient also adjusts their own dose under an agreed protocol.

Therapeutic range

The band of INR values a prescriber sets for an individual patient, based on why that patient is anticoagulated. It is a clinical decision recorded in the file: software follows it, it does not choose it.

Time in therapeutic range (TTR)

The share of a follow-up period during which a patient’s INR sat inside their therapeutic range, given as a percentage. It is the usual way of summarising how steady control has been over months, rather than at a single visit.

Vitamin K antagonist (VKA)

The class of oral anticoagulant this kind of follow-up exists for, acting by blocking the clotting factors that depend on vitamin K. Warfarin is the molecule used in Canada; acenocoumarol and phenprocoumon are used elsewhere. Their effect shifts with diet, illness and other medicines, which is the reason they are monitored by INR.

Weekly dose

The total amount a patient takes across a full week. Vitamin K antagonists are usually adjusted on that total rather than tablet by tablet, because their effect accumulates over days.