What is Prediction Marker/Impedance Ratio (IR)?
The Impedance Ratio (IR), derived by an MF-BIA measurement, and is defined in the ESPEN Blue Book as a “Newer way to evaluate cell membrane function” and a “reliable guide to prognosis” of patients in intensive care Units.
IR is the ratio between the impedance measured at 200 kHz and 5 kHz.
How does it work?
In a healthy subject at 5 kHz, the Impedance or resistance to the flow of the current will be High because the current cannot penetrate the cell membrane. It therefore only measures the Extra-cellular water (ECW).
At the higher 200 kHz frequency, the current is strong enough to penetrate the cell membrane wall. Thus, the impedance is lower and measure both inside (ICW) and outside the cells (ECW) – total body water (TBW = ECW+ICW).
The greater the variance between these two values the healthier the body tissues.
Expressed as a ratio, the closer to 1, the less healthy the cell becomes.
Prediction Marker / Impedance Ratio have become increasingly popular as a measure of patient health. Not least in the following applications:
- Predictor of Outcome before surgery
- Identify potential high risk surgery patients
- Track effectiveness of surgery and rehabilitation recovery
- Raise awareness of potential complicated clinical courses of patients during hospitalization
- Prognosis of patients in intensive care units.
- Assessment of cellular health & hydration status.
The greater the variance between the two impedance values at 5 kHz and 200 kHz, the healthier the body cells. To allow easy monitoring of change, these figures are expressed as a ratio. A ratio closer to 1.00 indicates poor cellular health or extreme fluid overload.