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As the prevalence of diabetes continues to soar, primary care practitionersare confronted with an ever-increasing tide of patients presenting with signsof diabetic nephropathy.
Rather than immediately turning these patients over to a nephrologist,primary care providers can play an important role in maintaining the continuumof care throughout all stages of the disease.
A symposium at the 65th Scientific Sessions of the American DiabetesAssociation (ADA) in San Diego and reports from new research also presented atthe June 10–14 meeting identified the most effective nephropathyscreening and care management techniques for the primary care setting.
EVALUATING EFFECTIVENESS OF SCREENS
Undiagnosed chronic kidney disease (CKD) is common in patients withdiabetes. Because of the likelihood that diabetic patients will developnephropathy—they account for roughly half of all CKD cases—ADArecommends that primary care clinicians screen all diabetic patients forkidney disease on an annual basis.
"Unfortunately, this is not a consistent practice," saysMatthew Weir, MD, professor of medicine and director of nephrology at theUniversity of Maryland.
Inconsistent screening is just one problem with the process of identifyingdiabetic nephropathy. How best to screen for it isanother.
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Guidelines in the U.K. recommend annual urinary albumin and serumcreatinine evaluations, with a nephrology referral when serum creatininelevels are >150 µmol/l (1.7 mg/dl). But screening strategies based onserum creatinine >150 µmol/l (1.7 mg/dl) alone, or albuminuria alone,fail to identify a considerable number of patients with clinically relevantCKD, according to results of a population-based cohort study in an urban U.K.setting.
Microalbuminuria has been widely accepted as the primary predictor of CKD.But at the June ADA meeting, other researchers shared separate findingsdemonstrating that this marker does not identify all people with hyperglycemiaand CKD who are at risk for end-stage renal failure. The investigators reportthat while microalbuminuria increases in prevalence and severity as CKDadvances, patients can exhibit severely impaired renal function withoutmanifesting albuminuria.
"CKD may be missed if clinicians rely on [microalbuminuria] fordiagnosis of diabetic nephropathy in patients with hyperglycemia,"concludes George Bakris, director of the hypertension research center at RushUniversity Medical Center in Chicago, who presented the findings.Nonalbuminuric patients with diabetes and CKD are understudied, Bakris andcolleagues conclude, and may represent a large number of high-riskpatients.
Serum creatinine levels alone aren't sufficient either, Bakris says.Because muscle mass and kidney function naturally decline as we age,"serum creatinine is a relatively crude marker for kidney function,especially in people over 65," Bakris says. "A number may bewithin the normal range, but the patient could have lost 30–40% ofkidney function."
GFR A BETTER SCREENING TOOL
That's why an increasing number of clinicians are using calculatedestimates of the glomerular filtration rate (GFR) to diagnose and stagechronic kidney disease. Recent ADA guidelines recommend estimated GFR as amore precise means of determining the level of renalfunction.1 Themethod also is backed by the National Kidney Disease Education Program(NKDEP), an initiative of the National Institutes of Health that seeks toenhance public awareness of preventive therapy.
Calculating the GFR is simple (see FYI). "Your receptionist cancalculate the GFR," Bakris says. Others concur. "It's easilydownloadable on your PDA or desktop," says Katherine R. Tuttle, MD,director of The Heart Institute of Spokane. "It's designed to be verysimple; it uses existing information on patients."
GFR also is gaining the support of many laboratories. "Nationally,it's anticipated that within the next year, all major laboratories will reportGFR," Bakris says. Although the estimated GFR must be ordered separatelyfrom serum creatinine for patients >20 years old, there is no extracharge.
PROMOTING A CONTINUUM OF CARE
While potential therapeutic advances are cause for cautious optimism (seesidebar, "Emerging Diabetic Nephropathy Therapy"), the carecomponent remains critical to successful outcomes. With primary care providersalready overburdened and nephrologists lacking in numbers, diabetic patientswho have or are at risk for CKD sometimes fall through the cracks.
"Primary care doctors are trying to hand them off too early;nephrologists are reluctant to accept them," says nephrologist Tom F.Parker III, MD, of Dallas Nephrology Associates. Indeed, in some regions,access to a nephrologist is hard to come by, and the primary care provider mayneed to continue to take a lead in managing several CKD-related issues. As theGFR drops, providers should be paying more attention to anemia, proteinconsumption, hyperkalemia, phosphate imbalances, and calcium.
Because an estimated 23 times more people who have kidney disease die ofcardiovascular disease than develop end-stage renal disease, experts adviserigorous techniques to inhibit CVD for all diabetic patients with nephropathy."An LDL [cholesterol] level <70 [mg/dl] should be the target,"says Mark Molitch, MD, director of Northwestern University Feinberg School ofMedicine's Endocrinology Clinic. "Aspirin should be routine. Stresstesting should be carried out when necessary."
Some people believe that any diabetic patient should be on anangiotensin-converting enzyme (ACE) inhibitor and an angiotensin receptorblocker (ARB)—even those who don't have kidney disease, Parker says. Henotes, however, that to date the efficacy of this approach remainsanecdotal.
So when is it time to make a referral to a nephrologist? "As the GFRapproaches 30–45 [ml/min/1.73 m2], consultation with anephrologist is indicated," Molitch says. He also recommends thatprimary care providers refer patients to a nephrologist if they areuncomfortable managing rapidly falling GFR or rising urinary albumin levels,or if they have difficulty controlling hypertension, hyperkalemia, elevatedparathyroid hormone levels, or anemia.
Similarly, ADA advises considering "referral to a physicianexperienced in the care of diabetic renal disease either when the GFR hasfallen to <60 ml/min/1.73 m2 or if difficulties occur in themanagement of hypertension or hyperkalemia." Consultation with anephrologist is recommended when the GFR is <30 ml/min/1.73 m2.Early referral can reduce cost, improve quality of care, and keep people offdialysis longer.2(For a complete discussion on the treatment of nephropathy, see the ADAposition statement on diabeticnephropathy3 and theNational Kidney Foundation practice guidelines forCKD.4)
Referring a patient to a nephrologist doesn't mean severing the existingrelationship, however. "The primary care physician should remain activein the care of the patient, not simply `hand off' the patient to anephrologist," Molitch says.
Relying on available support systems helps facilitate this continuedcommunication. Newer electronic medical records enable easy routing of visitrecords and test results between offices. Support staff also help keep thelines of communication open. "Office nurses, nurse educators, andnephrology nurses are vital links in the process," Molitch says.
| Emerging Diabetic Nephropathy Therapy In preliminary studies, a promising therapy appeared to decreasealbuminuria in patients with type 2 diabetes and diabetic nephropathy who wereon standard antihypertensive therapy of angiotensin-converting enzyme (ACE)inhibitors, angiotensin receptor blockers (ARBs), or both, according toresearch presented at the ADA meeting. The agent under investigation, ruboxistaurin (Arxxant, Lilly), is aselective inhibitor of protein kinase C beta, an enzyme believed responsiblefor producing microvascular damage in people with kidney disease. In the second of two trials of ruboxistaurin, 123 subjects with persistentalbuminuria despite standard treatment were randomized either to ruboxistaurin(32 mg/day) or placebo. Those in the control group remained on ACE inhibitorsand/or ARBs. Subjects in the experimental group experienced significantreductions in albuminuria after 1 month of treatment, and decreases persistedthroughout the trial. The control group did not fare as well. "The placebo group got thebest of what we have available now, but predictably, proceeded to lose kidneyfunction," says lead investigator Katherine R. Tuttle, MD, director ofThe Heart Institute of Spokane. The scientists hope to advance to phase III trials in the near future.Tuttle expresses optimism about ruboxistaurin and other emergingtherapies. "Hopefully before too long we'll have a menu of things with which totreat vascular complications. We're getting to the point where we'll actuallybe treating the affected organs," she says.
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| Nutrition Guide for Diabetic Nephropathy Following a nutritionally sound diet is an integral part of managingdiabetic nephropathy, but it's not easy. "Competing dietary needs make devising an appropriate dietdifficult," admits Katherine R. Tuttle, MD, director of The HeartInstitute of Spokane. Even the most savvy and motivated patients need assistance, and they needit early in the disease process. "Health care providers who see people at stages 1 and 2 (seechart on page 8) need to bethinking about nutrition, and not waiting until people are just about readyfor dialysis," says Jane H. Greene, RD, CSR, a registered dietitiancertified as a renal specialist by the American Dietetic Association. At thesestages, people should continue working with their diabetes dietitian, as mostof the nutrition guidelines are similar to those endorsed by the AmericanDiabetes Association (ADA) (see FYIbelow).1 For patients who have diabetic nephropathy, start by sharing the followingnutritional guidelines, which should allow for a seamless transition fromnutritional counseling provided in accordance with the ADA recommendations.The most substantive addition is keeping closer tabs on potassium andphosphorus; protein recommendations are the same.
FYI The American Diabetes Association recommendations for medicalnutrition therapy can be found online athttp://care.diabetesjournals.org/content/vol28/suppl_1/. More information about becoming certified as a renal dieteticspecialist is available from the American Dietetic Association:www.eatright.org/Public/Other/index_certfication.cfm.
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Footnotes
The estimated glomerular filtration rate (eGFR) can be calculated easily byaccessingwww.kidney.org/kls/professionals/gfr_calculator.cfm.
The National Kidney Foundation is registering reviewers for theforthcoming K/DOQI Clinical Practice Guidelines: Diabetes and CKD. Thedraft for these guidelines is expected to be ready for review in 2006.
To sign up, visitwww.kidney.org/professionals/kdoqi/kdoqi_form.cfm.
References
2. Levinsky NG: Specialist evaluation in chronic kidney disease: Toolittle, too late. Ann Intern Med 137: 542–543, 2002.
3. American Diabetes Association: Nephropathy in diabetes (PositionStatement). Diabetes Care 27(Suppl. 1): S79–S83, 2004.
4. Levey AS, Coresh J, Balk E, et al.: National Kidney Foundationpractice guidelines for chronic kidney disease: Evaluation, classification,and stratification. Ann Intern Med 139: 13–147, 2003.
1. American Diabetes Association: Standards of medical care indiabetes (Position Statement). Diabetes Care 28 (Suppl. 1): S4–S36, 2005.
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10% oftotal caloric intake; total fat <30% of overall intake.