01Principles and purposeThe professional or clinical skill and the decisions it supports.
Data interpretation in prescribing turns observations into an action that improves treatment. The action may be a dose change, additional assessment, a temporary hold or deliberate continuation. Start by identifying what the result measures and whether it describes the current patient. A creatinine concentration, indexed eGFR and calculated creatinine clearance are related but not identical. An HbA1c represents a different time window from a capillary glucose reading. A sitting blood pressure may miss postural symptoms. These distinctions matter because a correct number can answer the wrong clinical question if its meaning is not examined before a prescription is changed.
Trends and treatment goals give a result context. Repeated stable kidney values support a chronic dose category more reliably than a single result during vomiting. Recurrent overnight hypoglycaemia may reveal excessive background insulin even when an occasional daytime value is high. A new low pressure with dizziness may warrant review despite an apparently desirable clinic target. The interpretation should make the clinical link explicit: which medicine is affected, why the new data change its benefit or risk, and what further observation will show whether the adjustment was appropriate. Avoid treating an abnormal result as a command detached from the person and the indication.
Key points
- Identify the decision the data should inform, then check identity, units, timing, reliability and the relevant baseline before changing treatment.
- Combine the result with symptoms, examination, actual medicine use and the indication. A number within a population range can still be unsafe for the individual, and an abnormal value can sometimes be an expected monitored response.
- Distinguish stable impairment from acute deterioration. A chronic dose table cannot safely substitute for assessment of dehydration, sepsis, hypoxia or rapidly evolving organ injury.
- For selected metformin prolonged-release tablets at stable GFR 30–44 mL/min, the total daily dose must not exceed 1,000 mg; below GFR 30 the product is contraindicated.
- Do not transfer the dose rule for one medicine or indication to another. Apixaban AF age, weight and creatinine criteria differ from its acute VTE schedule, and SGLT2 cardiorenal benefit differs from glucose efficacy.
- If glucose readings show recurrent hypoglycaemia, reassess the regimen and individual target rather than intensifying solely because another isolated measurement is high.
- Write the revised dose or explicit hold, the reason, the expected effect and the verification plan. Communicate the next actual administration so the patient is not left to infer the change.
02Situations and prioritiesThe context, relevant information and actions that matter most.
Compare with a relevant baseline and ask whether the difference is large enough, persistent enough or symptomatic enough to alter care. Consider measurement variability and the expected response to recent treatment. A sudden clinically important change deserves prompt assessment even if a repeat value is planned.
Determine which renal measure, weight criterion, concentration target or physiological endpoint the product or guideline actually uses. A dose-reduction rule with several conditions must be applied logically, not approximately. Write each criterion and its supplied value so another clinician can reproduce the result.
Ask about missed doses, timing, technique, supply and interactions. An apparently ineffective regimen may not have been taken consistently, while a concentration or clinical response may reflect recent catch-up dosing. Increasing the written dose without understanding use can create excessive exposure once the original problem is corrected.
A tighter glycaemic target, lower blood pressure or stronger anticoagulant effect is not inherently better in every context. Evaluate hypoglycaemia, falls, bleeding, renal injury and treatment burden alongside the intended benefit. The appropriate adjustment may be simplification or risk reduction rather than escalation.
03Assessment and interpretationHow to gather information, assess the situation and recognise uncertainty.
Consider the information, its meaning and its limitations before deciding what follows.
- 01
Validated laboratory values and clinical trajectory - Why
- Establish whether the result supports a stable dose category or acute assessment.
- Interpretation and limitations
- Check patient identity, units, sample date and previous measurements. A laboratory eGFR during rapidly changing creatinine is not a dependable steady-state clearance. Assess intake, urine output and physiological stability before applying a chronic medicine dose limit to an acutely unwell person.
- 02
Patterns of glucose, pressure or other response data - Why
- Relate medicine timing to benefits and adverse effects.
- Interpretation and limitations
- Review multiple appropriately obtained readings when the decision depends on a pattern. For glucose, note meals, exercise, symptoms and insulin timing; for pressure, include posture and symptoms where relevant. A single convenient measurement can conceal the period in which treatment is causing harm.
- 03
A complete current administration history - Why
- Distinguish pharmacological failure from inconsistent delivery or a recent change.
- Interpretation and limitations
- Verify the actual dose and formulation, not only the repeat list. Ask who gives the medicine and how missed or extra doses are handled. For devices, observe technique when poor delivery could explain the data. Reconcile changes made during a recent admission before adding further treatment.
- 04
The exact product and indication-specific recommendation - Why
- Translate the supplied data into an evidence-based prescribing action.
- Interpretation and limitations
- Check current dose criteria, contraindications and monitoring guidance for the selected product. A guideline may recommend a class while the product defines an individual dose boundary. If the patient lies near a threshold or outside the studied population, seek appropriate advice rather than inventing a proportional reduction.
04Worked approachesCases with ordered reasoning, an action and a check of the outcome.
01Worked exampleAdjust metformin to a stable renal dose ceilingA 72-year-old takes metformin prolonged-release 2,000 mg orally with the evening meal and dapagliflozin 10 mg orally daily for type 2 diabetes. eGFR values over 3 months are 39, 38 and 38 mL/min/1.73 m². She is well hydrated without acute illness or hypoxia; HbA1c is 50 mmol/mol against an agreed 48–58 target. Her metformin tablets contain 500 mg.+
- 1Identify the stable renal category rather than assuming an acute kidney injury from one result. The supplied repeated eGFR values place her in the selected metformin product’s 30–44 band, which permits a maximum total of 1,000 mg per day.
- 2Compare prescribed exposure with that ceiling: 2,000 mg daily is 1,000 mg above the permitted maximum. The revised 1,000 mg dose is two 500 mg prolonged-release tablets, representing a 50% reduction from the current daily amount.
- 3Give the final medicine action: reduce metformin prolonged release to 1,000 mg orally with the evening meal and update the supply instructions. Review dapagliflozin separately; reduced glucose efficacy at this eGFR does not automatically remove its eligible protective role in this stable patient.
- 4Arrange review of tolerability, glucose symptoms and renal trajectory, with repeat HbA1c around 3 months for this illustrative stable plan and earlier assessment if illness develops. Independently verify two 500 mg tablets equal 1,000 mg, confirm the old four-tablet instruction is inactive and explain the change and sick-day contact plan to the patient.
02Pattern interpretationRespond to recurrent low glucose during treatmentAn adult using a hypoglycaemia-causing medicine has repeated low readings or compatible symptoms.+
- 1Assess and treat any current hypoglycaemia first, then obtain the timing and circumstances of previous episodes. Confirm the glucose units, meal pattern, actual doses and kidney function, and ask about driving or activities in which recurrence could be dangerous.
- 2Look for a pattern connected to treatment timing, such as overnight lows, missed meals or increased activity. Consider whether a changed organ state or reduced intake has made a previously suitable regimen excessive; do not use a single later high value to dismiss the repeated lows.
- 3Review the individual glycaemic target and agree an appropriate dose reduction, simplification or alternative with the responsible diabetes clinician. The specific change depends on the agent and pattern; a generic percentage reduction is not a universal substitute for that assessment.
- 4Provide an explicit next-dose plan, increased monitoring during the adjustment and advice about recurrence. Check whether the change reduces hypoglycaemia while preserving acceptable symptom control, and revisit the plan if the glucose pattern remains unsafe.
03Criteria interpretationApply an anticoagulant rule without importing another indicationA patient’s age, weight or kidney data prompt review of a DOAC dose.+
- 1Confirm the indication and phase of treatment before opening the dose criteria. Atrial-fibrillation stroke prevention, acute venous thrombosis treatment and extended prevention can require different doses even in the same person.
- 2Use current product guidance and the required renal method, with verified weight and creatinine. For apixaban AF, evaluate the age, weight and serum-creatinine criteria individually and also apply the separate severe-clearance rule; do not reduce solely because the patient is elderly.
- 3Check interactions, bleeding, liver disease and adherence before issuing the revised or continued regimen. A dose that satisfies a numerical rule may still be unsuitable when another contraindication or serious clinical problem is present.
- 4Document the selected dose and the data supporting it, with a review interval appropriate to renal stability and other risks. Independently confirm that the indication in the prescription matches the one used to select the dose, especially after a recent thrombotic event or discharge.
05Relevant medicines and safetySpecific regimens and precautions when the skill involves prescribing.
Metformin prolonged release after the supplied renal review
For the stable worked case, 1,000 mg orally with the evening meal each day, supplied as two 500 mg prolonged-release tablets, replacing the previous 2,000 mg daily instruction.Below GFR 30 this product is contraindicated. Acute dehydration, hypoxia or serious illness can require a hold irrespective of the stable chronic dose; review liver risk, alcohol exposure and other causes of lactic-acidosis vulnerability.
06Feedback, follow-up and evidenceReview outcomes, seek feedback and identify what to improve.
- After a change, measure the effect at a time suited to the outcome. A symptom or glucose pattern may change quickly, whereas HbA1c takes longer to reflect the new regimen. Match the review interval to both the expected benefit and the risk of harm.
- Recheck organ function when the trajectory is uncertain or an acute illness develops. A chronic dose adjustment is based on the current stable state and should be revisited if that state changes, rather than treated as permanently correct.
- Confirm implementation by reviewing the label, medication list and actual dose taken. A verbal reduction can fail when an automated repeat or monitored dosage system continues the former tablet count.
- Document whether the action achieved its intended goal and whether another problem emerged. A lower dose that reduces toxicity but allows serious symptoms to recur may require an alternative treatment, not simply a return to an unsafe previous regimen.
07Special situationsVariants, exceptions and circumstances that change the usual approach.
Different numbers describe different time windows
HbA1c, a fasting glucose and an overnight sensor trace are complementary rather than interchangeable. Use the measurement that describes the part of the treatment pattern you are trying to change.
Criteria should be applied transparently
A rule requiring two of three conditions is different from a rule triggered by any one condition. Listing the inputs and marking which criteria are met prevents intuitive but unsupported dose reductions.
A dose ceiling is not a therapeutic target
A maximum describes an upper permitted exposure under specified conditions. The appropriate individual dose may be lower because of tolerability, treatment response or another risk, and reaching the ceiling is not itself evidence of good prescribing.
Continuation can be an active decision
When data remain acceptable and benefit is maintained, documenting why the current regimen should continue is a legitimate prescribing action. It should still include the next review and the circumstances that would change the decision.
08Common pitfallsFrequent interpretation and management errors.
- 01
Changing treatment from a single out-of-context laboratory number can miss sampling problems, acute illness or an important longer-term pattern.
- 02
Assuming that all medicines should be reduced at the same eGFR ignores differences in elimination, efficacy, indications and product dose rules.
- 03
Escalating treatment for an isolated high glucose despite recurrent hypoglycaemia can worsen the clinically more immediate problem.
- 04
Updating a narrative plan without changing the active prescription can leave the patient taking the old dose despite a correct interpretation of the data.