National Minimum Retesting Interval Guidance
This page provides selected Minimum Retesting Interval (MRI) information for pathology tests.
Guidance source
Source document: National minimum retesting intervals in pathology
Document: G147
Version: 2
Published: March 2021
Publisher: Royal College of Pathologists
Review date shown in source: March 2026
HbA1c – Monitoring patients with type 2 diabetes
Reference: B-E19
Test: HbA1c
Clinical situation: HbA1c monitoring in patients with type 2 diabetes.
Minimum retesting interval / recommendation:
Monitoring intervals should be tailored to the patient’s circumstances until blood glucose levels and glucose-lowering therapy are stable. Once stable on unchanged therapy, repeat HbA1c at six-monthly intervals.
Exceptions / additional guidance:
An HbA1c measurement performed less than three months after a previous measurement should be interpreted in the context of the direction of change rather than as a new steady-state measurement.
Source: NICE NG28, as referenced within RCPath G147.
Evidence level: B
HbA1c – Diagnosis of diabetes in an asymptomatic patient
Reference: B-E18
Test: HbA1c
Clinical situation: Diagnosis of diabetes using HbA1c in an asymptomatic patient.
Minimum retesting interval / recommendation:
An abnormal HbA1c result used for diagnosis in an asymptomatic patient requires confirmation rather than diagnosis being based on a single abnormal result. Confirmation may be by a further qualifying HbA1c or plasma glucose result.
Exceptions / additional guidance:
Refer to the approved source guidance for the circumstances in which HbA1c is appropriate for diagnosis.
Source: WHO guidance, as referenced within RCPath G147.
Evidence level: B
C-reactive protein (CRP)
Reference: B-SP7
Test: C-reactive protein (CRP)
Clinical situation: Repeat CRP testing.
Minimum retesting interval / recommendation:
Do not routinely repeat CRP within 24 hours of the initial request.
Exceptions / additional guidance:
The approved guidance identifies an exception for paediatric requests.
Source: RCPath G147 – National minimum retesting intervals in pathology.
Evidence level: D
Vitamin B12 and folate
Reference: B-G10
Test: Vitamin B12 and folate
Clinical situation: Monitoring vitamin B12 and folate deficiency.
Minimum retesting interval / recommendation:
Routine repeat measurement is not required in established vitamin B12 or folate deficiency.
Exceptions / additional guidance:
Further testing may be appropriate where there is an inadequate response to treatment, in accordance with the circumstances described in the approved guidance.
Source: RCPath G147 – National minimum retesting intervals in pathology.
Evidence level: D
Using this guidance
Minimum Retesting Intervals depend on both the pathology test and the clinical situation. Where more than one recommendation may apply to a test, the relevant clinical context should be established before selecting a recommendation.
This page supports access to approved Minimum Retesting Interval guidance and does not replace clinical judgement or applicable local protocols.
Where the information required for a particular test or clinical situation is not provided on this page, users should refer to the approved source guidance rather than infer a Minimum Retesting Interval.