The Pharmacist’s Guide To Interpreting Lab Values

Laboratory results are central to safe medication management, yet a number rarely tells the whole clinical story. A creatinine result can alter an antibiotic dose, a potassium concentration can signal danger in a patient taking an ACE inhibitor, and a mildly raised ALT may require review rather than automatic cessation of treatment. Pharmacists need to interpret these findings alongside the medicine, indication, patient history and timing of the test.

In Australia, pharmacists often work with fragmented information from community pharmacies, general practices, hospitals, pathology providers and residential aged-care services. The result may appear in a discharge summary, a patient’s My Health Record or a printed pathology report. A consistent approach helps pharmacists identify medication-related harm, communicate clearly with prescribers and support patients without presenting themselves as the sole diagnostician.

Start With The Clinical Question

Begin by identifying why the test was ordered and what decision it is meant to support. Is the clinician checking whether a medicine is working, assessing toxicity, confirming a diagnosis or establishing a baseline before treatment? The same result can have different implications depending on that purpose.

Check the patient’s age, weight, pregnancy status, hydration, comorbidities and recent illness. Ask when the sample was collected in relation to the dose. A lithium concentration taken shortly after administration cannot be interpreted like a properly timed trough level. Similarly, a glucose result after a meal should not be treated as equivalent to a fasting measurement.

Review the complete medication list, including over-the-counter products, complementary medicines and recent short courses. Non-steroidal anti-inflammatory drugs, laxatives, antacids and herbal products can all influence laboratory values or medicine exposure. In a busy pharmacy in Melbourne or Brisbane, a brief medicines reconciliation may reveal the explanation for an unexpected result.

Read The Result In Context

Reference intervals are statistical guides, not rigid boundaries between health and illness. They can vary between pathology laboratories because of different analysers, methods, populations and reporting conventions. Always read the interval printed on the report rather than relying on a remembered range from a textbook.

Australian pathology reports commonly use SI units, such as mmol/L for electrolytes and glucose, μmol/L for creatinine and g/L for haemoglobin. Confirm the units before acting. A result may also be affected by collection conditions, haemolysis, fasting status, posture, exercise and sample delay. If a value conflicts sharply with the patient’s presentation, contact the pathology service or prescriber before making a medication change.

Trends are usually more useful than isolated values. A stable creatinine over several months may be less concerning than a rapid increase, even if both values remain within the laboratory interval. Compare current and previous results, calculate the direction and pace of change, and document the clinical context that might explain it.

Kidney Function And Dose Decisions

Renal function is one of the most important areas of laboratory interpretation for pharmacists. Serum creatinine alone is an incomplete measure because it is influenced by muscle mass, age, diet and acute illness. The estimated glomerular filtration rate, or eGFR, provides useful information for many medicines, but it may be unreliable during rapidly changing kidney function, acute kidney injury, dialysis or extremes of body size.

Medication decisions should follow the dosing information for the specific medicine. Some recommendations use eGFR, while others, particularly older product information and certain clinical trials, refer to creatinine clearance calculated by the Cockcroft–Gault equation. Do not substitute one measure automatically. When the dose threshold is close, ask the prescriber or renal pharmacist to confirm the intended method.

Look for medicines that accumulate or increase renal risk, including metformin, gabapentinoids, digoxin, lithium, some antimicrobials and direct oral anticoagulants. A patient with vomiting, diarrhoea, fever or reduced oral intake may experience a rapid decline in kidney function before a new pathology result is available. Explain warning symptoms, assess hydration and escalate promptly when toxicity or acute kidney injury is possible.

Liver Tests And Medicine Safety

Liver panels need careful interpretation because each component reflects a different process. ALT and AST may indicate hepatocellular injury, while alkaline phosphatase and gamma-glutamyl transferase can be associated with cholestasis, biliary disease, alcohol exposure or enzyme induction. Bilirubin and albumin provide additional information, but albumin changes slowly and may be affected by nutrition or inflammation.

A mild isolated enzyme elevation does not automatically mean a medicine must be stopped. Review the timing of treatment, alcohol intake, viral illness, metabolic disease and other hepatotoxic exposures. Paracetamol overdose, jaundice, marked enzyme elevation, confusion, bleeding or severe abdominal symptoms require urgent medical assessment rather than routine follow-up.

Medicines such as statins, anti-tuberculosis therapies, valproate, methotrexate and some antifungals may require liver monitoring under particular circumstances. Pharmacists should check the approved product information and local protocol, then communicate the exact result and trend. Patient education can include practical oral and general health resources; for example, an appropriate oral health resource may support counselling when dry mouth, oral ulceration or poor intake complicates medicine use.

High Risk Medicines And Monitoring

Therapeutic drug monitoring is most useful when a medicine has a narrow therapeutic index, a clear relationship between concentration and effect, and a validated sampling time. Lithium, digoxin, phenytoin, vancomycin and some immunosuppressants require attention to dose history, collection time, adherence and interacting medicines. A concentration without its sampling details can be misleading.

For lithium, review renal function, thyroid function, sodium status, fluid intake and medicines such as NSAIDs, ACE inhibitors, angiotensin receptor blockers and thiazide diuretics. For digoxin, consider renal function, potassium, magnesium, age and symptoms; nausea, visual disturbance, confusion and arrhythmia deserve urgent escalation. For warfarin, interpret the INR against the treatment indication and target range, while checking antibiotics, alcohol changes, illness and missed doses.

Anticoagulant management also illustrates the limits of routine laboratory testing. PT/INR does not measure the effect of apixaban or rivaroxaban in a way that supports ordinary dose adjustment. A normal result does not exclude clinically significant anticoagulant exposure. In Australia, PBS access and brand changes can influence medicine histories, so confirm the exact product, strength and last dose before advising.

Communicate Results Across Care

A pharmacist’s value often lies in translating a laboratory result into a clear, actionable message. Use a structured format: identify the patient and medicine, state the result and date, describe the relevant trend, explain the suspected medication connection, and propose the next clinical step. “Creatinine has risen from 92 to 168 μmol/L over two weeks after an NSAID was started; the patient is oliguric and taking an ACE inhibitor” is more useful than “renal function is worse.”

Escalate according to urgency. Severe hyperkalaemia, a rapidly falling haemoglobin, suspected overdose, a dangerously high INR, severe hypoglycaemia or signs of sepsis should not wait for a routine fax or future appointment. Contact the prescriber, emergency service or poisons information pathway as appropriate, and record who was contacted and what advice was provided.

Shared records can help, but they do not replace direct communication. A discharge summary may omit a community medicine that affects renal function, while a pathology report may not reach the pharmacy. Encourage patients to keep an updated medicine list and, where suitable, ensure relevant information is available through My Health Record. In rural and remote Australia, telehealth and collaboration with Aboriginal Community Controlled Health Services may be essential when specialist access is limited.

Build A Practical Monitoring Workflow

Create a medicine-specific monitoring plan rather than ordering tests without a decision attached. Record the baseline result, target or threshold, timing of the next test, responsible clinician and action required if the value changes. Include patient instructions, such as when to collect a trough level or which symptoms require immediate care.

Use reliable sources, including the Australian Medicines Handbook, Therapeutic Guidelines, product information, local hospital protocols and Therapeutic Goods Administration safety alerts. Recommendations can differ between medicines and patient groups, and renal or hepatic impairment may require specialist input. A professional clinical perspective can also prompt reflective discussion about communication, uncertainty and the practical limits of medication monitoring.

Make follow-up visible. Electronic reminders, pharmacy notes, aged-care communication systems and documented handover can prevent a monitoring plan from disappearing after dispensing. If the patient misses pathology testing, cannot obtain the medicine, or reports new symptoms, treat that information as part of the clinical assessment rather than as an administrative issue.

Laboratory finding	Medicines commonly affected	What the pharmacist should check	Escalation concern
Rising creatinine or falling eGFR	Metformin, lithium, digoxin, gabapentinoids, some antimicrobials	Acute illness, hydration, dose, renal dosing method and recent NSAID use	Rapid change, reduced urine, confusion or suspected toxicity
High potassium	ACE inhibitors, ARBs, spironolactone, trimethoprim	Repeat result, haemolysis, kidney function and interacting medicines	Severe elevation, weakness, palpitations or ECG concern
Raised ALT or AST	Statins, valproate, methotrexate, antifungals	Baseline, trend, alcohol, viral illness and other hepatotoxic drugs	Jaundice, marked elevation, bleeding or altered mental state
Low haemoglobin	Anticoagulants, antiplatelets, NSAIDs	Bleeding symptoms, iron status, stool changes and medicine history	Syncope, chest pain, haemodynamic instability or active bleeding
Abnormal INR	Warfarin, interacting antibiotics and other medicines	Target range, dose history, diet, alcohol and bleeding symptoms	Very high INR, head injury or any significant bleeding
Low glucose or high HbA1c	Insulin, sulfonylureas, corticosteroids and diabetes medicines	Meal pattern, adherence, renal function and glucose records	Severe hypoglycaemia, altered consciousness or recurrent episodes

Use this framework to turn pathology data into safer, patient-centred medication decisions. Review one high-risk medicine in your dispensary today, confirm its monitoring requirements, and document a clear pathway for acting on the next result. Consistent interpretation, timely escalation and strong communication can prevent avoidable harm across Australian pharmacy practice.