Laboratory tests, including but not limited to assessment of renal function in older patients

Overview

Interpreting laboratory tests in older patients requires age-adjusted reference ranges and clinical context, since several common tests have different "normal" implications in older age than in younger adults
Standard reference ranges are often derived predominantly from younger, healthier populations and may not reflect what is truly normal (or truly abnormal) in an older, frailer cohort

eGFR declines physiologically with age - a "reduced" eGFR in an otherwise well 85-year-old may reflect expected ageing rather than acute kidney disease, though it still matters for drug dosing regardless of cause
ESR rises with age independent of disease, reducing its specificity as an inflammatory marker in this population
Mild anaemia, mild hyponatraemia, and mildly abnormal thyroid function are more common and sometimes multifactorial in older patients, requiring judgement about clinical significance rather than reflexive investigation/treatment of every mild deviation
Vitamin D deficiency is highly prevalent in older adults, particularly those with reduced sun exposure/mobility

No single reference range applies universally - interpretation requires weighing the result against age-expected physiological change, the patient's known baseline, and the overall clinical picture rather than a fixed population cutoff alone
Interpret results against the patient's own baseline (if available) and clinical context, not just the population reference range - a "significant" change from a patient's own baseline can be clinically important even within the population-normal range, and vice versa
Avoid over-testing/over-treating mild, non-progressive abnormalities that are common and often benign in this population (see judicious use of investigations)

Renal function/drug dosing, anaemia of chronic disease/multifactorial anaemia, subclinical thyroid dysfunction, vitamin D deficiency

A test result that would prompt urgent action in a younger patient may represent a stable, longstanding, and clinically insignificant finding in an older patient - trend and clinical context matter more than a single value against a generic reference range

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