Chronic kidney disease in elderly people: disease or disease label?
BMJ 2016; 352 doi: https://doi.org/10.1136/bmj.h6559 (Published 18 January 2016) Cite this as: BMJ 2016;352:h6559
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This piece is both timely and well-argued. As a geriatrician, I have been exercised by this topic since its inception. Not only does the information not help greatly prognostically with one's older patient (as the authors amply demonstrate), but its apparent simplicity also can mislead. Many doctors just see 'GFR of 62 mLs per min' and presume that that is what it means, and what it actually is.
The eGFR is calculated using the MDRD formula and, as described, is expressed as mLs/min per unit (1.73 m^2) body surface area [BSA]. This BSA is that of the mythical 'average young adult' the physiologists teach us about in medical school. Over the past few years, in the context of discussing renal function, I have asked virtually all my junior doctors and medical students to estimate patients' surface areas. No-one has ever had a clue. However, they confidently, and fairly accurately, estimate patients' weight from the end of the bed.
They are usually very surprised when I then estimate the renal function using the Cockroft-Gault [CG] formula for them, using a smartphone app.
For example, a 90 year old woman of 1.52 m (5 foot) and 50 kg (7 stone 12 lbs) has an 'ideal' BMI of 21.5, and her body surface area is 1.45 m^2. If she has a creatinine of 90, her eGFR (calculated using CG) is 29 mL/min. Using the MDRD formula, this result translates into approximately 1.73/1.45 times this result, i.e. 35 mL/min - a 20% difference. To put it another way, if the same patient weighed 75 kg, the CG eGFR would be 44 mL/min - approximately 50% greater! The smaller and frailer the patient the greater the difference between the MDRD uncorrected for BSA and the CG eGFR.
This order of magnitude variance due to BSA can easily be the difference between a person having renal function apparently safe for i.v. contrast, and a GFR low enough to be of major concern.
It is high time we used sensible and practical measures in a clinically useful way, rather than an abstract and ‘artificial statistical construct’ which is poorly understood by many (most?) doctors and which unnecessarily worries many GPs and patients.
Competing interests: No competing interests
Ellam and colleagues should have had the courage to place "disease" in (parenthesis). Or did the BMJ (house style) not let them?
Chronic Kideney Disease (CKD) is no more a disease than "fever" or "anaemia". It is a measure of physiological deviation which MAY reflect disease and merits the attention of medicine, a profession whose three main tenets are diagnosis, diagnosis and diagnosis.
How can we sensibly lump together such an amorphous group as a ninety year old female with pipe-stem arteries; a younger male with renal artery stenosis; those with hydronephrosis due to obstructive uropathy; and those patients with one of the many causes of interstitial renal disease? And in terms of a comprehensive differential diagnosis that is just a taster.
But that is what the apalling abbreviation CKD invites us to do and even to consider management as though these heterogeneous people had a single shared "disease" with a common treatment strategy. This is dangerous nonsense.
I would like to invite the international medical community to consider barring the expression CKD and replace it with "impaired renal function - cause and management to be determined".
Competing interests: No competing interests
Physicians treat sickness by probing the past and present (diagnosis), prescribing medicine or surgery, and predicting the future (prognosis). But sometimes physicians are wrong, because they’re so focused on esoteric scientific knowledge, that they ignore plain common sense by overlooking obvious questions, such as the patient’s contact with toxins and addictions, both of which are common causes of sickness. A wise physician knows that knowledge plus common sense is wisdom, but knowledge minus common sense is nonsense.
Competing interests: No competing interests
Graphs Reveal the Progression of Kidney Disease: A single measurement is not enough.
This article, and the rapid responses generated, discuss the significance of a “low” egfr calculated from a serum creatinine measurement in the elderly person, with the potential to diagnose a disease when none exists but also the potential, if a “low” egfr is ignored, to miss a condition that might respond to an intervention eg discontinuing a nephrotoxic medication, treating an infection or removing obstructing pathology.
All “abnormal” results may be indicating important pathology but also may be a “false” positive due to the reference ranges provided for elderly patients indicating “abnormality” in some without disease of clinical significance or with a kidney disease that is stable. When an egfr is below the reference ranges it is the clinician's responsibility to identify those with progressive disease of significance. The report of an “abnormal” value is, therefore, an indication to search for previous measurements of plasma creatinine and to generate a plan for sufficient further testing to enable an assessment of rate of progression. Repeat measurements may need to be immediate if insufficient previous values are available to aid assessment and when there are substantially changed values from the most recent measurements. Repeat measurement can often be planned to be collected at intervals of time in the future appropriate to the situation to generate an adequate sequence of data to assess if there is a decline or to establish stability.
Measurements should be considered as a sequence of measurements and not in isolation. The merits of considering sequential measurements of kidney function over time is not discussed in this review. They are critical to enable the clinician to assess if there is a rate of deterioration in excess of that anticipated with age. With sufficient sequential data an acceleration in a previous rate of deterioration, with a “change point”, can indicate a reason for deteroration eg introduction of a nephrotoxic medication.
Sequences of creatinine measurements are best presented as a graphic of the reciprocal of plasma creatinine or as the egfr (1). The importance of further investigations (eg measurement of urine albumin/creatinine ratio, examination of the urinary deposit and renal imaging) is increased when there is progressive change suggesting deterioration or an acceleration in deterioration not due to ageing. Graphical presentations should be provided by laboratory services or by clinic or hospital IT systems. Algorithms that analyse data statistically for trends in data and for change-points in sequential data, have been developed but are underused for assisting with the interpretation of sequential data and to provide alerts when the rate of deterioration changes. (2) (3)
(1) Rayner H, Thomas M, Milford D. (2016) "Plot all the Dots: Graphs Reveal the Progression of Kidney Disease", CHAP 3, Understanding Kidney Disease. Springer, London. http://www.theisn.org/education/education-topics/general-nephrology/item...
(2) Knapp, MS, Smith, AFM, Trimble, IM, Pownall, R, Gordon, K (1983). Mathematical and statistical aids to evaluate data from renal patients. Kidney International, 24,474-486.
(3) Morgan EJ, Will EJ. Selection, presentation and interpretation of biochemical data in renal failure. Kidney International 1983, 24,438-445.
Competing interests: No competing interests