Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 59-year-old woman is evaluated during a routine follow-up visit. She was recently diagnosed with type 2 diabetes mellitus and hyperlipidemia. She feels well. Medications are metformin, atorvastatin, and aspirin.

Physical examination findings and vital signs are normal. BMI is 27.

Laboratory studies reveal a serum creatinine level of 0.9 mg/dL (79.6 µmol/L), an estimated glomerular filtration rate of >60 mL/min/1.73 m², and normal urinalysis results.

Which of the following is the most appropriate diagnostic test to perform next?

A: 24-Hour urine collection for protein
B: Kidney ultrasonography
C: Spot urine albumin–creatinine ratio
D: No additional testing

MKSAP Answer and Critique

The correct answer is C: Spot urine albumin–creatinine ratio. This item is available to MKSAP 16 subscribers as item 73 in the Nephrology section.

A spot urine albumin–creatinine ratio is indicated to evaluate this patient for chronic kidney disease (CKD). She has type 2 diabetes mellitus, a population that is at risk for CKD, and testing for microalbuminuria is appropriate. The National Kidney Foundation and the American Diabetes Association recommend annual testing to assess urine albumin excretion in patients with type 1 diabetes of 5 years’ duration and in all patients with type 2 diabetes starting at the time of diagnosis by measuring the albumin–creatinine ratio. Microalbuminuria is defined as an albumin–creatinine ratio of 30 to 300 mg/g; diagnosis requires an elevated albumin–creatinine ratio on two of three random samples obtained over 6 months. Patients with diabetes and microalbuminuria are at increased risk for progression of CKD and cardiovascular disease. Use of ACE inhibitors or angiotensin receptor blockers delays progression in patients with proteinuric kidney disease or in patients with diabetes and microalbuminuria, underscoring the importance of early detection.

The gold standard for measuring urine protein excretion is a 24-hour urine collection. However, this test is cumbersome and unreliable if not collected correctly. Patients have a difficult time accurately collecting urine for 24 hours, in addition to keeping it on ice. Therefore, the National Kidney Foundation Kidney Disease Outcomes Quality Initiative (NKF KDOQI) recommends use of urinary ratios on random urine samples as an alternative method of estimating proteinuria in the clinical assessment of kidney disease. Furthermore, a 24-hour urine collection may not diagnose low-grade microalbuminuria.

Kidney ultrasonography can be performed once a diagnosis of CKD is made but should not be used to screen for CKD.

Although this patient has an estimated glomerular filtration rate of >60 mL/min/1.73 m² and normal urinalysis results, she has diabetes and should therefore be evaluated for CKD.

Key Point

• The National Kidney Foundation and the American Diabetes Association recommend annual testing to assess urine albumin excretion in patients with type 1 diabetes mellitus of 5 years’ duration and in all patients with type 2 diabetes starting at the time of diagnosis by measuring the albumin–creatinine ratio.

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