The Prediction Marker is discussed in the ESPEN “Blue” Book, Basics in Clinical Nutrition text, as a “newer way to evaluate cell membrane function” and as a “reliable guide to prognosis” (of patients in intensive care units). The Prediction Marker is unique to Bodystat and since its inception has been used in many research areas.
Basics in Clinical Nutrition, Fourth Edition, ESPEN (2011)
The Prediction Marker or Impedance Ratio is the ratio between the impedance measurement at 200 kHz and 5 kHz. At 200 kHz the current is strong enough to penetrate the cell membrane and therefore total body water (TBW) can be measured. However, at 5 kHz the membrane cannot be penetrated and only Extracellular Water (ECW) can be measured. Intracellular water (ICW) is derived by TBW-ECW. 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. Figure 3 illustrates the normal ranges as experienced by Bodystat.
Figure 4 illustrates actual data of a “dying” male. Note that the curve is much flatter compared to that of the healthy male. When considering this data, the steeper the curve, the healthier the body cell.
Expansion of ECW and loss of ICW are typical features of systemic illness, arising from protein leakages into the extracellular space and loss of intracellular protein.
Loss of intracellular potassium and extracellular accumulation of sodium result in an increased whole-body exchangeable Na+-K+ ratio, which is a strong predictor of mortality in surgical patients. The resistance of the cell membrane at 5 kHz is therefore significantly reduced in the case of critical illness and the difference between the impedance values at 5 kHz and 200 kHz is markedly closer to each other resulting in a higher ratio, indicating cellular deterioration.