EVIDENCE-BASED ANSWER
Screening diabetic patients for microalbuminuria identifies those who may benefit from treatments that delay progression to renal failure (strength of recommendation: B, based on extrapolation from Level 1 treatment studies of patients with microalbuminuria).
No research has determined the best method for screening for microalbuminuria, or whether screening in primary care populations will produce better long-term outcomes. No studies have examined the role of microalbuminuria screening after angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers (ARBs) have been instituted for other indications.
Evidence summary
Patients with diabetes mellitus have a 20% to 40% lifetime risk for development of nephropathy, and microalbuminuria is the earliest easily detectable marker of renal damage.1 Improved control of blood sugar2,3 and blood pressure4 decreases but does not completely prevent development of microalbuminuria and progression to overt kidney failure. ACE inhibitors and ARBs have been shown to diminish this progression even in the absence of hypertension (the latter in type 2 diabetes only) (Table).
No prospective randomized trials of screening have been reported. There is uncertainty about what method of screening is most effective and practical in primary care settings.10 Expert opinion recommends diagnosing microalbuminuria after 2 positive test results,1 but whether repeated tests improve diagnostic accuracy is still controversial.10
A large randomized controlled trial showing better long-term renal and vascular disease outcomes would be needed to give screening for microalbuminuria a strength of recommendation of A. Recruiting patients for such a study, and interpreting its results, would be difficult: many subjects would have other indications, such as hypertension or congestive heart failure, warranting use of potentially renoprotective medications.
TABLE
Reno- and cardioprotective efficacy of treatments for diabetic patients with microalbuminuria
| DM type | Medication | NNT | Time (years) | To prevent endpoint |
|---|---|---|---|---|
| 1 | ACE inhibitor (Captopril) | 7.9* | 2 | Clinical proteinuria5 |
| 2 | ACE inhibitor (Enalapril) | 6.3* | 5 | Macroalbuminuria6 |
| 2 | ACE inhibitor (Enalapril) | 2.4* | 7 | Significant proteinuria7 |
| 2 | ARB (Losartan) | 3.6 | 3.4 | End-stage renal disease8 |
| 2 | ACE inhibitor (Ramipril) | 4 | 4.5 | Cardiovascular disease9 † |
| *Normotensive subjects | ||||
| †Myocardial infarction, revascularization procedure, stroke, cardiovascular death, congestive heart failure requiring hospitalization, overt nephropathy, renal dialysis, or laser treatment for retinopathy | ||||
| DM, diabetes mellitus; NNT, number needed to treat; ACE, angiotensin-converting enzyme; ARB, angiotensin receptor blocker | ||||
Recommendations from others
The American Diabetes Association recommends annual screening for microalbuminuria—after 5 years of established type 1 disease, and at time of diagnosis for type 2 diabetes without macroalbuminuria. Initial screening can use 1 of 3 methods: measurement of the albumin-to-creatinine ratio in a random, spot collection; 24-hour collection with creatinine, allowing the simultaneous measurement of creatinine clearance; timed (eg, 4-hour or overnight) collection. At least 2 of 3 tests measured within a 6-month period should show elevated levels before a patient is said to have microalbuminuria.1
CLINICAL COMMENTARY
Stephen A. Wilson, MD
University of Pittsburgh Medical Center, St. Margaret Family Practice Residency, Pittsburgh, Pa
Blood pressure control and ACE inhibition improve mortality and morbidity for patients with diabetes mellitus type 2. Therefore, maximize ACE inhibitor or ARB doses, as tolerated, and aim for a blood pressure of 110–120/70–80 mm Hg (130/85 mm Hg is the maximum).
Using this plan, I do not routinely screen for microalbuminuria—which is, at best, a surrogate marker for nephropathy and poor blood pressure control—unless I believe it will work as an educational and motivational tool for patients who are less committed to self-care.
If serum creatinine becomes elevated, a 24-hour urine collection to examine volume, creatinine clearance, and protein can be used to help develop a negotiated care plan with the patient, which may or may not include referral. Until there is different evidence about screening and treatment options for microalbuminuria, I see no need to screen when the above plan is in effect.