Age Charts to Assess Kidney Function

Blog entry written on: Kidney trajectory charts to assist general practitioners in the assessment of patients with reduced kidney function: a randomised vignette study, (bmjebm-2021-111767)

Authors: Michelle Guppy, Paul Glasziou, Elaine Beller, Richard Flavel, Jonathan E Shaw, Elizabeth Barr, Jenny Doust.


It’s time to incorporate age into the chronic kidney disease guidelines to better categorise patients’ risk. 

Age-related kidney function charts could do just that. To illustrate the folly of ignoring age, consider two patients.

Phyllis is aged 76 and visits her GP for the results of her annual health check.  She’s very healthy for her age, and she’s on no medications.  The GP checks her kidney function as part of a routine screen and discovers that whilst it is a similar result to 12 months ago, it has now dropped to the range considered “chronic kidney disease” (but is average for her age).  The GP considers whether to tell Phyllis she has chronic kidney disease? The GP queries what the average kidney function of a woman Phyllis’ age is, and wonders if there is a tool that could help him determine that.

Brad visits his GP for his annual check-up.  Brad is a much younger man, but he recognises the importance of keeping on top of his health because several family members have diabetes and heart disease.  Brad gave up smoking 5 years ago and he’s keen to stay healthy.  The GP checks Brad’s kidney function and discovers that it is within the ‘normal’ range, but has dropped a few points in the preceding 12 months.  The GP queries what rate of kidney function decline in a younger person should be something to worry about.  The GP wonders if there is a tool that could help determine that.

These scenarios are played out in GP consultations on a daily basis.  GPs make decisions about their patients’ kidney function and whether it needs to be further investigated, or whether a ‘watch and wait’ strategy is acceptable. How do GPs make these decisions? Currently guidelines use absolute cut-off values for kidney function, without any reference to a patient’s age.  However this can be problematic, with a patient’s kidney function dropping by 50% from its peak before being recognised as abnormal.  In a young person, this rapid drop could be cause for concern and further investigation, whereas in an older person, the slow drop may just be a result of age, and as long as the person is careful with what medications they take, may not need any active treatment.

Our paper (Kidney trajectory charts to assist general practitioners in the assessment of patients with reduced kidney function: a randomised vignette study) (bmjebm-2021-111767) presents a “kidney age trajectory chart” as a tool to assist GPs in making decisions about patients’ kidney function, taking age into account in addition to the guidelines. Our chart plots eGFR across the 5th to 95th percentiles and compares this to patient age.  We tested this chart on GPs to see how it might change their thinking about a patient’s kidney function. We found that GPs who used the chart were more likely to think an older woman’s kidney function was normal for her age.  We also found that GPs who used the chart were more likely to correctly recognise a younger male patient’s kidney function decline as problematic.  We think it is time to incorporate patient age into the kidney disease guidelines to assist in making sensible patient-centred decisions.

Example of kidney trajectory charts (Image created by the authors. Used with permission)

Image of a chart


Blog Authors

Dr Michelle Guppy

Institute for Evidence-Based Healthcare, Bond University, Queensland, Australia
COI: Dr Guppy received a grant from Therapeutic Guidelines Ltd to undertake this research

Dr Paul Glasziou

Institute for Evidence-Based Healthcare, Bond University, Queensland, Australia
COI: reports grants from the Australian National Health and Medical Research Council during the conduct of the study.


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