Letter to the Editor

After listening to the podcast and reading the article about drug dosing in chronic kidney disease,1 I am still perplexed about the best way to estimate renal function (for drug-dosing purposes) for patients in wheelchairs. I have asked many colleagues without success.

I do many group home visits where the majority of patients are in wheelchairs and fed by PEG (percutaneous endoscopic gastrostomy), hence my question.

Penny Beirne
Pharmacist, Sydney


Author's response

Darren Roberts, one of the authors of the article, comments:

The clinical issue raised here relates to disuse atrophy of the muscles which results in decreased creatinine production. It is therefore anticipated that a patient in a wheelchair with significant chronic kidney disease may have a serum creatinine concentration that is in the reference range. This means that routine laboratory reporting of the estimated glomerular filtration rate (eGFR) will incorrectly indicate that the patient has a ‘normal’ GFR.

Although there are limited data regarding this patient group, published studies have confirmed this hypothesis, and the limitations of simple approaches based on the serum creatinine concentration and either eGFR or estimated creatinine clearance (eCrCl). Both the eGFR2,3,4 and eCrCl2,4,5,6 commonly overestimated CrCl as measured on a 24-hour urine collection1,3,5,6 or measured GFR (mGFR).4,5 The actual CrCl measured on a 24-hour urine collection was approximately 70–80% lower than estimates using eGFR or eCrCl in two studies,2,6 and even lower in patients who were quadriplegic.6 In another study, the 24-hour urinary CrCl was on average 17 mL/minute higher than the corresponding mGFR.4

A few studies indicate that of the approaches which use a single blood sample, cystatin C-based methods are superior to creatinine-based methods.5,7 However, these are not widely available.

Taken together, eGFR and eCrCl are more likely to be inaccurate in patients in wheelchairs, but interpatient variability precludes an adjustment factor being applied universally. Until more information is available, including data confirming the accuracy of cystatin C-based approaches, a CrCl based on 24-hour urine collection may be the simplest option, particularly in those with an indwelling urinary catheter. However, since this may also overestimate the actual GFR, then an mGFR should be considered if clinically indicated. Therapeutic drug monitoring should also be used when appropriate.



  1. Stefani M, Singer RF, Roberts DM. How to adjust drug doses in chronic kidney disease. Aust Prescr 2019;42:163-7.
  2. Chikkalingaiah KB, Grant ND, Mangold TM, Cooke CR, Wall BM. Performance of simplified modification of diet in renal disease and Cockcroft-Gault equations in patients with chronic spinal cord injury and chronic kidney disease. Am J Med Sci 2010;339:108-16.
  3. Braley-Berthoumieux E, Gamé X, Marque P, de Boissezon X, Rischmann P, Castel-Lacanal E. Étude de la sensibilité de l’échographie rénale comme moyen indirect d’évaluation de la fonction rénale chez les patients porteurs d’une vessie neurologique, à partir d’une cohorte de 103 patients [Study of the sensitivity of renal ultrasonography as an indirect means of assessing renal function in patients with neurogenic bladder, from a cohort of 103 patients]. Prog Urol 2014;24:1114-9.
  4. Mingat N, Villar E, Allard J, Castel-Lacanal E, Guillotreau J, Malavaud B, et al. Prospective study of methods of renal function evaluation in patients with neurogenic bladder dysfunction. Urology 2013;82:1032-7.
  5. MacDiarmid SA, McIntyre WJ, Anthony A, Bailey RR, Turner JG, Arnold EP. Monitoring of renal function in patients with spinal cord injury. BJU Int 2000;85:1014-8.
  6. Mirahmadi MK, Byrne C, Barton C, Penera N, Gordon S, Vaziri ND. Prediction of creatinine clearance from serum creatinine in spinal cord injury patients. Paraplegia 1983;21:23-9.
  7. Jenkins MA, Brown DJ, Ierino FL, Ratnaike SI. Cystatin C for estimation of glomerular filtration rate in patients with spinal cord injury. Ann Clin Biochem 2003;40:364-8.

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Penny Beirne

Pharmacist, Sydney

Darren M Roberts

Staff specialist, Department of Clinical Pharmacology and Toxicology, St Vincent’s Hospital, Sydney

Staff specialist, Department of Renal Medicine, Canberra Hospital and Community Services, Canberra

Staff specialist, Department of Renal Medicine and Transplantation, St Vincent’s Hospital, Sydney

Conjoint associate professor, St Vincent’s Clinical School, University of New South Wales, Sydney