Renal Function Assessment and Urinalysis Quiz

Renal Function Markers

• Why pharmacists care: Many drugs need dose adjustments for patients with reduced kidney function, as kidneys are their primary elimination route.

• Example: Bactrim (sulfamethoxazole/trimethoprim) requires renal dose adjustments. Use drug references (e.g., Micromedex, Clinical Pharmacology) for recommendations.

Measuring Renal Function

• Two Main Methods: Blood tests and urine analysis.

Blood Tests

• Serum Creatinine (SCr): Key marker for pharmacists, byproduct of muscle creatine. Cleared by the kidneys, not reabsorbed, synthesized, or metabolized. Levels affected by muscle mass and red meat. Changes lag behind renal function decline. A rise indicates past 1-2 day function decline

• Blood Urea Nitrogen (BUN): Less specific than SCr. Elevated BUN can signify kidney problems, dehydration, or GI bleeding.

• Serum Electrolytes: (sodium, potassium, chloride, magnesium, phosphorus). Abnormal levels indicate potential kidney issues. Potassium especially important, as abnormal levels affect the heart.

Urine Tests

• Urine Output: Total urine volume over time. Reduced output may indicate fluid intake issues or kidney problems.

• Urinalysis: Chemical, physical, and microscopic analysis of urine.

• Albumin-to-Creatinine Ratio (ACR): Measures albumin and creatinine in the urine, helps detect kidney damage in diabetes or hypertension. High ACR indicates damage.

Estimated Glomerular Filtration Rate (eGFR)

• Definition: Volume of fluid filtered per minute by the glomerulus (kidney's functional unit). Normal range for young adults: ~120 mL/min/1.73m².

• Factors influencing eGFR: Changes with SCr levels. Age, sex, and body size are fixed variables. Useful for determining chronic kidney disease (CKD) severity.

Creatinine Clearance (CrCl)

• Calculation: Primarily used for drug dosing via the Cockcroft-Gault equation.

• Cockcroft-Gault Equation: A formula used to estimate CrCl for drug adjustments. Serum Creatinine (SCr) in the denominator.

• Weight Considerations: Different weights (ideal body weight, total body weight, adjusted body weight) used based on Body Mass Index (BMI) and weight excess. Use of different weights is crucial.

• Using the correct body weight: Using incorrect weight in calculations leads to either under or overestimation of CrCl.

• eGFR vs. CrCl: eGFR used for clinical diagnosis and prognosis. CrCl used primarily for drug dosing.

Renal Function Calculation Equations

• Modified Diet in Renal Disease (MDRD): Equation to calculate eGFR.

• Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI): A more commonly used equation for eGFR, since it's less biased.

Clinical Applications & Caveats

• Elderly Patients: Muscle loss reduces SCr, potentially overestimating CrCl. Important to carefully adjust calculations.

• Amputations: Loss of muscle mass affects SCr-based calculations.

• Unstable SCr: Not a reliable indicator if fluctuating, since it lags behind kidney function changes

Case Example: Mr. MG

• A 65-year-old male with UTI prescribed Bactrim. Patient parameters: 119.5kg, 5'9", BMI 38.8, and stable SCr 3.08mg/dL. The correct weight for CrCl calculation involves using adjusted body weight (90.2kg).

• Calculated CrCl: 31mL/min

• Dose Adjustment: No need for Bactrim dose adjustment in Mr. MG as his CrCl is above 30mL/min.

Additional Renal Function Measurements

• BUN (Blood Urea Nitrogen): Elevated levels can indicate kidney issues or dehydration. Less specific than SCr. Normal range: 6-20mg/dL

• Electrolytes: Kidney maintains electrolyte balance, especially potassium, which can cause serious heart problems in abnormality.

• Urine Output: Reduced urine output (less than 0.5mL/kg/hour over 24 hours) is an early sign of kidney or dehydration issues.

• Urinalysis: Essential tool for identifying conditions like diabetes, urinary infections, and glomerular damage. Look for physical characteristics (color, clarity), chemical findings (glucose, protein, leukocyte esterase), and microscopic analysis (red blood cells, white blood cells, bacteria, epithelial cells).

This quiz explores crucial lab values and concepts related to kidney function and urinalysis. It covers topics such as the identification of kidney damage, significance of specific lab results, and the Cockcroft-Gault Equation. Test your knowledge on renal health indicators and urinalysis interpretation.