What is the urine potassium creatinine ratio for a patient with urine potassium of 28.5 mmol/L and urine creatinine of 44.8 mg/dL?

Calculating Urine Potassium-to-Creatinine Ratio

The urine potassium-to-creatinine ratio for this patient is 6.36 mmol/g, which indicates renal potassium loss.

Calculation Steps

• First, convert urine creatinine from mg/dL to g/L:

  • 44.8 mg/dL = 0.448 g/L 1

• Calculate the ratio:

  • Urine potassium: 28.5 mmol/L
  • Urine creatinine: 0.448 g/L
  • Ratio = 28.5 mmol/L ÷ 0.448 g/L = 63.6 mmol/g 1

• Convert to standard units:

  • 63.6 mmol/g = 6.36 mmol/g (conventional units) 2

Clinical Interpretation

• A urine potassium-to-creatinine ratio >3.4 mmol/g suggests renal potassium loss with sensitivity of 67.6% and specificity of 67.5% 2

• For comparison, traditional diagnosis of renal potassium losses uses:

  • 24-hour urine potassium ≥20 mEq/day during hypokalemia 1
  • Random urine K/Cr ratio >1.5 mmol/g suggests renal potassium loss 3

Clinical Applications

• This ratio helps differentiate renal from non-renal causes of potassium abnormalities 3

• Elevated ratios (>3.4) may indicate:

  • Diuretic use
  • Primary hyperaldosteronism
  • Bartter or Gitelman syndrome
  • Renal tubular acidosis 3

• Normal or low ratios (<1.5) may suggest:

  • Poor potassium intake
  • Gastrointestinal losses
  • Cellular shifts of potassium 3

Monitoring Recommendations

• For patients with abnormal potassium levels, especially those on medications affecting potassium (ACE inhibitors, ARBs, diuretics), regular monitoring of both serum potassium and creatinine is recommended 4

• The frequency of monitoring should follow a risk-based approach based on kidney function 4

• When initiating or adjusting doses of medications affecting the renin-angiotensin system, check serum potassium and creatinine within 2-4 weeks 4

Limitations of the Test

• Spot urine samples show moderate correlation with 24-hour collections 2

• Results can be affected by:

  • Hydration status
  • Time of collection
  • Dietary intake
  • Medications 5

• Biological variability can vary by >20% between measurements 5