Table 3. Evaluation of proteinuria

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Do the words nephrology or kidney evoke terrible memories of the renal section that you never completely understood?

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This article provides a step-by-step process for evaluating kidney function and offers information on early management of chronic kidney disease (CKD) in a primary-care setting. Identifying CKD facilitates appropriate treatment of this very destructive disease.

The clinical scenario of Mr. H will be used throughout the article to illustrate this step-by-step process.

  • Aged 55 years
  • The patient’s status one year post-coronary stenting included a history of obesity, type 2 diabetes mellitus, hypertension, and cardiovascular disease (CV D).
  • Mr. H is a current tobacco user with a 30-pack year smoking history.
  • Present medications include insulin, metoprolol (Lopressor, Toprol), and hydrochlorothiazide (HCTZ) (HydroDIURIL, Microzide).
  • Mr. H has retinopathy, a fourth heart sound, +2 lower extremity edema, and peripheral neuropathy.
  • Serum creatinine (sCr) 2.4 mg/dL (up from 2.0 mg/dL one year ago), blood urea nitrogen (BUN) 30 mg/dL, potassium 4.8 mEq/L, hemoglobin (Hb) 10.4 g/dL, HbA1c 9.8%, and spot urine albumin/creatinine 2,500 mg/g.

When Mr. H returns for a four-month follow-up visit, should the focus be on weight management or on treating his diabetes? Do you provide advice on smoking cessation? Do you attempt to evaluate kidney function?

Most clinicians have likely seen an increase in abdominal girth and obesity among the patient population. The rates of type 2 diabetes continue to increase as well, leading to a rise in the prevalence of CKD. Diabetes is the foremost cause of CKD and end-stage renal disease (ESRD) in the United States, followed closely by hypertension.1 Given this knowledge, it is unethical not to evaluate each at-risk patient for the potential development of CKD.

Dialysis has made tremendous advances in prolonging patients’ lives once ESRD is reached, but it is not an ideal way to live. Dialysis strongly affects the physical, financial, and emotional aspects of a patient’s life. Evaluating renal function, especially in people with CKD risk factors, is of paramount importance.

Step 1: Identify patients at increased risk for CKD

Individuals who are older than age 60 years, have diabetes, hypertension, CVD, family history of CKD, history of autoimmune disease, recurrent urinary tract infections, nephrolithiasis, systemic infections, neoplasms, or history of acute kidney injury are at increased risk for CKD and must be screened (Table 1).

Clinical scenario 1: Based on his medical history, Mr. H should definitely be screened for CKD. Diabetes, hypertension, and CVD (not to mention elevated sCr and albuminuria) place Mr. H at increased risk for developing CKD.

Step 2: Screen patients at increased risk for CKD

Based on the National Kidney Foundation’s Kidney Disease Outcomes Quality Initiative guidelines, the diagnosis of CKD is determined by the presence of kidney damage and/or the level of kidney function, irrespective of diagnosis.2

Table 1. Risk factors for chronic kidney disease

Age older than 60 years
Family history of CKD
Type 2 diabetes mellitus
History of autoimmune disease, recurrent urinary tract infections, ­nephrolithiasis, systemic infections, neoplasms, or acute kidney injury

In clinical terms, CKD is defined as: (1) the persistent and usually progressive reduction in glomerular filtration rate (GFR) (i.e., GFR <60 mL/minute/1.73 m2 for three months or longer, with or without kidney damage); and/or (2) albuminuria (>30 mg of urinary albumin per gram of urinary creatinine) based on spot urine collection.2

In the outpatient setting, kidney function is determined by calculating the estimated GFR (eGFR). An abbreviated eGFR can be calculated using the patient’s age, race, sex and sCr concentration. Most labs report the eGFR with the metabolic panel. A normal eGFR is approximately >100 mL/min/1.73 m2. The eGFR gives a percentage of kidney function. For example, if the eGFR is 40, the patient has approximately 40% of kidney function remaining, meaning that approximately 60% of kidney function has been lost.

Clinical scenario 2: Mr. H’s sCr, age, race, and sex produce an eGFR of 36. Last year, his sCr was 2.0 mg/dL with an eGFR of 42. Since he has had an eGFR of <60 for at least three months, we can conclude that Mr. H has CKD. Mr. H should be informed that he has approximately 36% of his kidney function remaining.

The eGFR is critical to calculate, and clinicians should be cautioned against using sCr alone to establish kidney function. Serum creatinine concentration is determined mainly by muscle mass and dietary animal-protein intake, independent of renal function. If a patient has extremes in muscle mass and/or dietary animal-protein intake, sCr will not accurately determine renal function.

For example, a black male bodybuilder, aged 25 years, may have an sCr of 1.5 mg/dL with a normal eGFR, while a thin, white woman aged 80 years with a history of hypertension with the identical sCr may have an eGFR of 30.

The young bodybuilder is on the extreme side in both muscle mass and dietary intake of animal protein, so his sCr is more reflective of these factors than of his true level of kidney function. The elderly thin woman has very little muscle mass and a poor diet.