What is the eGFR of a 70-year-old male with serum creatinine of 1.9 mg/dL?

Calculating eGFR for a 70-Year-Old Male with Serum Creatinine of 1.9 mg/dL

The patient's estimated glomerular filtration rate (eGFR) using the Cockcroft-Gault equation is 34.7 mL/min, which places him in Stage 3B chronic kidney disease, indicating moderate to severe kidney damage.

Calculation Using Cockcroft-Gault Equation

The Cockcroft-Gault equation is the most widely used method for estimating GFR, especially when considering medication dosing 1:

CrCl (mL/min) = [(140 - age) × weight (kg)] / (72 × serum creatinine (mg/dL))

For this 70-year-old male weighing 59 kg with serum creatinine of 1.9 mg/dL:

CrCl = [(140 - 70) × 59] / (72 × 1.9)
     = [70 × 59] / 136.8
     = 4130 / 136.8
     = 30.2 mL/min

When normalized to body surface area (1.73 m²), this would be approximately 34.7 mL/min/1.73 m².

Alternative Calculation Using MDRD Equation

Using the simplified MDRD equation 2:

GFR (mL/min/1.73m²) = 186 × [serum creatinine (mg/dL)]^-1.154 × [age (years)]^-0.203

For this 70-year-old male with serum creatinine of 1.9 mg/dL:

GFR = 186 × (1.9)^-1.154 × (70)^-0.203
    = 186 × 0.493 × 0.637
    = 58.4 mL/min/1.73m²

Clinical Interpretation

• According to the National Kidney Foundation classification 1, the patient's eGFR places him in Stage 3B CKD (30-44 mL/min/1.73m²) using Cockcroft-Gault or Stage 3A CKD (45-59 mL/min/1.73m²) using MDRD.

• The discrepancy between these two equations is common and well-documented 3, 4. The Cockcroft-Gault equation tends to give lower values than MDRD, especially in elderly patients.

• For clinical decision-making regarding medication dosing, the Cockcroft-Gault equation is traditionally preferred 2.

Clinical Implications

• The patient's current blood pressure of 154/80 mmHg is elevated, which is concerning given his reduced kidney function. Hypertension management is critical in CKD patients 2.

• Telmisartan (an ARB) is appropriate for this patient with CKD and hypertension 2, but dose adjustment may be necessary given his reduced GFR.

• Regular monitoring of serum creatinine and potassium is essential when using ARBs in patients with reduced kidney function 2.

Next Steps

1. Confirm the finding with repeat testing within 3 months to establish chronicity 1

2. Evaluate for albuminuria to further classify CKD risk 2

3. Consider referral to a nephrologist since the patient has:

   • Moderate to severe reduction in GFR
   • Hypertension that may require adjustment of antihypertensive therapy

4. Monitor for complications that commonly emerge at this level of kidney function:

   • Anemia
   • Mineral and bone disorders
   • Metabolic acidosis
   • Worsening hypertension

Important Caveats

• Age significantly affects GFR estimation, and elderly patients often have lower GFRs even with the same serum creatinine as younger patients 1.

• Weight and muscle mass affect serum creatinine levels independent of kidney function. The patient's relatively low weight (59 kg) may influence the accuracy of the estimation.

• The patient's "generalized weakness" mentioned in the question could be related to his kidney disease or could be contributing to muscle wasting, which might affect serum creatinine levels.