10 High Yield Nephrology Pearls for Clinical Practice and the ABIM Board Exam (Part 1 of 2)

Recently, I read an article on some very useful chronic kidney disease (CKD) pearls to help those healthcare providers who are not nephrologists care for their patients and also prepare for the ABIM Internal Medicine Board exam at the same time. The article was titled “The Top 10 Things Nephrologists Wish Every Primary Care Physician Knew” by Paige NM et al and basically stated: early recognition of kidney disease is essential in order to begin measures to prevent progression and complications such as kidney failure, cardiovascular disease, and premature death. I have decided to break the content into two parts; the first half will be discussed in this post:

1. A “Normal” Creatinine Level May Not Be Normal

• Make sure to take muscle mass, age, sex, height, and limb amputation into account
• Consider using MDRD or Cockcroft-Gault equations to calculate glomerular filtration rate (GFR)
• MDRD and Cockcroft-Gault equations are imprecise at high values for GFR (low values for serum creatinine)

2. Know the Medications That Falsely Elevate Serum Creatinine Levels

• Trimethoprim-sulfamethoxazole and cimetidine decrease secretion of creatinine
• Both medications can increase creatinine level by as much as 0.4 – 0.5mg/dL
• An increase in creatinine level is a true decrease in GFR only if there is also a corresponding increase in BUN

3. Patients with Decreased GFR or Proteinuria Need to be Evaluated for the Cause

• Urine dipstick detects concentration of albumin in urine
• Urine concentration can affect dipstick results therefore a quantitative estimation of proteinuria is required to evaluate dipstick proteinuria
• The preferred quantitative test is spot urine protein to creatinine ratio (accurate & more convenient than 24-hr urine collection)
• A urine protein to creatinine ratio ≥ 1 has a higher risk of progression of CKD

4. Early-Stage CKD Should Have Periodic Evaluation and Intervention to Slow Progression

• Try and avoid nephrotoxic agents (NSAIDs, aminoglycoside antibiotics, and radiocontrast)
• Monitor and control blood pressure with a goal of <130/80 mmHg
• Angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin II receptor blockers (ARBs) may slow progression of CKD, especially in patients with proteinuria
• Monitor phosphorous, calcium, and parathyroid hormone levels in all patients with stage 3 to 4 CKD
• Patients with CKD are at higher risk of cardiovascular events and should be on a baby aspirin, and a lipid lowering agent with goal LDL <100mg/dL (Maybe <70mg/dL for LDL in patients with CAD and CKD)
• Consider referral and co-management with a nephrologist if a patient has CKD progression, active urine sediment and/or stage 3 CKD
• ALL patients with Stage 4 – 5 CKD should be referred to a nephrologist

5. DO NOT Discontinue an ACEI or ARB Because of a Small Increase in Serum Creatinine or Potassium

• Both ACEIs and ARBs are the drugs of choice to prevent progression of proteinuric CKD
• An increase of 20 to 30% of the creatinine level is acceptable
• Just make sure to confirm the creatinine stabilizes and does not continue to increase
• Also a serum potassium of 5.5 mEq/L is acceptable as long as it is stable and as long as the patient is aware of dietary restrictions
• Serum creatinine and potassium levels should be ordered within one week of increase in dose of ACEI or ARB
• If a patient has an increase in creatinine from 1.5 to 1.9 (<30% increase) CONTINUE THE ACEI
• If the same patient has an increase in creatinine from 1.5 to 2.2 (>30% increase) STOP THE ACEI

As chronic kidney disease is increasing world wide, we as primary care practitioners need to make sure we are doing our part to help catch this disease process early, slow down progression, and make referrals when necessary to nephrology. Stay tuned for Part 2 of this series, hopefully this provides some useful clinical pearls for your practice as well as ABIM Internal Medicine exam certification or re-certification preparation.

References:

1. Bakris GL et al. Angiotensin-Converting Enzyme Inhibitor-Associated Elevations in Serum Creatinine: Is this a Cause for Concern? Arch Intern Med. 2000; 160 (5): 685 – 693. PMID: 10724055

2. Douglas K et al. Meta-analysis: The Effect of Statins on Albuminuria. Ann Intern Med. 2006; 145 (2): 117 – 124. PMID: 16847294

3. Levey AS et al. Definition and Classification of Chronic Kidney Disease: A Position Statement from Kidney Disease: Improvemeng Global Outcomes (KDIGO). Kidney Int. 2005; 67 (6): 2089 – 2100. PMID: 15882252

4. Paige NM et al. The Top 10 Things Nephrologists Wish Every Primary Care Physician Knew. May Clin Proc. 2009 Feb; 84 (2): 180 – 186. PMID: 19181652