Calculate the spot urine potassium-to-creatinine ratio in mmol/mmol or mEq/g, convert common lab units, or reverse-solve potassium and creatinine.
Potassium to Creatinine Ratio Formula
The potassium-to-creatinine ratio is a urine index reported as mmol/mmol creatinine or mEq/g creatinine. It compares different analytes; it is not a percentage of a whole or the fractional excretion of potassium.
- R_g is the urine potassium-to-creatinine ratio in mEq/g; R_n is the ratio in mmol/mmol
- K is potassium (often urine potassium concentration, e.g., mmol/L or mEq/L)
- Cr_g is urine creatinine in g/L; Cr_n is urine creatinine in mmol/L. Convert mg/dL or µmol/L before dividing.
Use concentrations from the same spot urine sample. Divide potassium in mmol/L (numerically equal to mEq/L for potassium) by creatinine in g/L for mEq/g, or by creatinine in mmol/L for mmol/mmol. The calculator uses a nominal creatinine molar mass of 113.12 g/mol: 1 mmol/L = 0.11312 g/L and 1 mg/dL = 0.01 g/L.
How to Calculate Potassium to Creatinine Ratio?
The following example problem outlines how to calculate a urine potassium-to-creatinine ratio.
Example Problem #1:
- First, determine the urine potassium concentration.
- The urine potassium is given as 40 mmol/L.
- Next, determine the urine creatinine concentration.
- The urine creatinine is provided as 120 mg/dL.
- Finally, calculate the potassium-to-creatinine ratio using the equation above (convert creatinine to compatible units as needed).
K/Cr = K / Cr
The values given above are inserted into the equation below and the solution is calculated:
Cr = 120 mg/dL = 1.20 g/L. Using 113.12 g/mol, Cr = 1.20 / 0.11312 ≈ 10.6082 mmol/L. Thus 40 / 10.6082 ≈ 3.7707 mmol/mmol, or 40 / 1.20 ≈ 33.3333 mEq/g creatinine.
FAQ
What is the significance of the Potassium to Creatinine Ratio?
In clinical practice, the urine potassium-to-creatinine ratio (urine K/Cr) is commonly used when evaluating hypokalemia to help assess whether the kidneys are inappropriately wasting potassium. A higher urine K/Cr can suggest renal potassium loss (depending on context), while a lower value is more consistent with appropriate renal conservation. It is not a substitute for measuring blood (serum) potassium.
How often should the Potassium to Creatinine Ratio be tested?
How often it is checked depends on the clinical situation (for example, evaluation of hypokalemia or monitoring certain medications) and your clinician’s guidance.
Can diet affect the Potassium to Creatinine Ratio?
Yes. Higher dietary potassium intake (or supplements) can increase urinary potassium excretion and may increase a urine K/Cr result. In people with kidney disease or those taking certain medications, dietary potassium can also raise blood potassium. Discuss diet changes with a healthcare professional if you have kidney disease or abnormal potassium levels.
