Screening for chronic kidney disease in patients with diabetes: are we missing the point?

Merlin C Thomas*, GianCarlo Viberti and Per-Henrik Groop  About the authors

Screening for chronic kidney disease (CKD) should be an essential part of diabetes care. As an important health problem with high personal, social and financial costs, CKD meets any rational criteria for a screenable disease.¹ The natural history of diabetic kidney disease is well understood, and measurement of urinary albumin excretion is a simple, safe, precise and validated means of screening that is acceptable and convenient for patients. Albuminuria offers a means of identifying patients who are at an early and treatable stage of disease, and who have increased risk of not just renal failure, but also of cardiovascular disease and premature mortality.

Screening does not end once a patient has been classified as likely or unlikely to develop complications, however. Fundamentally, screening encompasses not only the test, but also subsequent diagnostic procedures and interventions. Indeed, when physicians screen for disease (or risk of disease), they assume a substantial degree of responsibility to intervene or at least respond to the result. For example, detection of a breast lump should be followed by appropriate investigation and intervention. It would be malfeasance to do nothing but watch and wait, because the prognosis of unmanaged disease is worse than the risks associated with investigation and intervention. The same principles must be applied to screening for CKD in patients with diabetes. Indeed, untreated albuminuria might be substantially more costly to the healthcare service than an untreated breast lump.²

Two key requirements for any type of screening are that there is an effective intervention available for patients identified as high risk, and that early access to this intervention leads to better outcomes. Even where screening is mandated and performed as part of the minimal cycle of diabetes care, however, usually only the test is undertaken and not any intervention. In Australian general practice, for example, diabetic patients who have macroalbuminuria are no more likely to receive an angiotensin-converting-enzyme inhibitor than those who have urinary albumin excretion in the normal range.³ Perceived blood pressure targets and the rate of use of aspirin for cardiovascular disease prevention are also similar in these two groups, even though the absolute benefits of intervention are highest in patients with macroalbuminuria.³ If the identification of risk is not followed by intensification of or changes in management, what is the purpose of screening?

For screening to be effective, the risk, cost or impracticality of treating all patients must outweigh any benefits that might be achieved by doing so, so that more costly or risky interventions are reserved for patients deemed to be at increased risk. Meeting treatment targets does, however, have substantial benefits for all patients with diabetes.⁴ Indeed, there is some support for the suggestion that maximal antihypertensive therapy, treatment with agents that block the renin–angiotensin system, and optimal glycemic and lipid control, should be undertaken in all patients with diabetes, regardless of the presence or absence of albuminuria. It is currently more expensive, however, to treat all diabetic patients than to treat just those at high risk of CKD, although the former strategy might be associated with increased quality-adjusted life expectancy.⁵ With the advent of cheaper generic drugs it will become more cost-effective to intensively treat all patients who have diabetes.

Although all health-care providers should ideally optimize clinical management of their patients before participating in a screening program, screening can be useful if there are inadequacies in preventive care. If a disease is generally undermanaged, substantial benefits can be achieved by identifying high-risk patients and, more importantly, working harder to reduce their risk. Screening is not so much an admission of these inadequacies as a way to make the most of a suboptimal system. The patient at the greatest absolute risk of cardiovascular disease will thus be the one whose LDL cholesterol you try to reduce even further, the one in whom you aim for additional blood-pressure lowering, the one for whom you prescribe aspirin, and the one on whom you spend more of your limited time and effort. Put simply, the greatest absolute risk reduction stands to be achieved in those who have the greatest absolute risk. Screening for CKD, and the risk stratification that such screening facilitates, is one way for busy clinicians to identify patients at greatest absolute risk and allocate limited resources to precisely where they are most needed.

Although the traditional characterization of patients as microalbuminuric or macroalbuminuric is useful for clinical studies, it is less relevant for the long-term management of individual patients with CKD. In clinical practice, screening is more than the process of instantaneous classification. There is no magic boundary between the stages of diabetic kidney disease, rather there is a continuous process of progression in which the level of urinary albumin excretion provides a marker of how far disease has progressed and what the likely outcomes will be if changes in management are not made. Moreover, reduction of albuminuria is associated with proportional renoprotective and cardioprotective effects, whether or not any arbitrary line is crossed.^{6, 7} Albuminuria should be considered a target for therapy, and a way of judging the absolute benefit of interventions and further optimizing risk reduction, rather than just a classification. To achieve the best outcomes, urine albumin excretion should be reduced to its lowest achievable level for as long as possible.

There exist numerous international guidelines on who should be tested for CKD, but testing is not the same as screening. Screening permits the identification of susceptible persons so that appropriate preventive actions can be taken. Intensive lifestyle modification, lowering of blood pressure and lipids, and improvement of glycemic control can improve renal and cardiovascular outcomes in patients with diabetes. In an imperfect world, targeting intensification of therapy to the high-risk patients with CKD who are identified by screening can optimize the use of limited resources and provide additional benefit. The finding of increased urinary albumin excretion must be a call to action. This, after all, is the point.

Competing interests

The authors declared no competing interests.

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