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mBCA measuring results: how to interpret the BIVA

The bioelectrical impedance analysis (BIA) has successfully been established as a diagnostic method for determining a patient’s body composition. The devices offered by seca, under the series seca mBCA, are renowned for their medically validated results and their significant amount of applications in clinical and ambulatory settings. During the measuring process with a seca mBCA, a weak alternating current is conducted through the patient’s body. The resistances that occur during this process are determined by measuring electrodes. The total resistance, known as the impedance, is a result of the resistance in body liquids that are high in electrolyte (Resistance, R) and the resistance of cell membranes (Resistance, Xc). Special analysis algorithms then calculate the exact amount of fat tissue and fat-free mass, as well as the body’s entire amount of liquids. The calculations of a BIA algorithm are based on the body’s physiological water balance and can be affected by changes in the body’s water distribution. Therefore, water inclusions can falsify the results and lead to a false estimation of too much fat-free mass and too little fat tissue. This can lead to misinterpreting a patient’s health status and can result in a misdiagnosis.

For this reason, the seca mBCA also measures the phase angle and completes the data by using the so called bioelectrical impedance vector analysis (BIVA).

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What is the BIVA?

During the BIVA process, the impedance is used as a vector for the fraction resistances; Resistance (R) and Reactance (Xc). The impedance value is adjusted according to the patient’s body size and applied into a coordinate system. This graphic display enables a detailed estimation of the patient’s hydration status as well as the body cell mass. The “body cell axis” runs from the top left to the bottom right quadrant. Shifting the vector along this line points at a change in Reactance (Xc) and an increase or decrease in cell mass. The “water axis” runs from the top right to the bottom left quadrant of the ellipse. Shifting the value along this line will result in a change in Resistance (R) which shows the volume of body liquids.

An elliptical reference range of the norm group, including three tolerance ellipsoids, (50%, 75%, 95%) helps evaluate the measuring data. Patients with a normal water supply are within the range of the green 50% ellipse. Strong anomalies towards the norm values can be seen in the 95% ellipse and outside of it. Malnutrition or heart insufficiencies are possible reasons for such divergences. If the values lie within the bottom pole of the reference area, a liquid surplus can be on hand. Values in the top part of the pole signify a strong dehydration. Cell loss, which can occur during malnutrition, is visible with values within the bottom right quadrant. Values in the top left quadrant signify a large amount of cell mass.

The following clinical examples serve for illustrating the capabilities of the BIA, BIVA and phase angle:

Patients afflicted with heart problems can suffer from being overweight or having a considerably increased body mass index (BMI) due to extracellular water retention. The BIA can prove that the weight and BMI increase are not related to a respective increase in fat tissue. The body composition chart (BCC), which shows the ratio between fat free mass and fat tissue, will also show that this patient’s fat free mass is increased and outside of the norm area. Usually these results would indicate an increase in muscular mass. By way of the BIVA, the fat free mass can now be further differentiated. In the following example; the BIVA offers information on how an increase in fat free mass is not related to increased cell mass. Instead, it illustrates a heightened water retention. A low phase angle will confirm this assumption as well.

Usually people with high muscular mass and low amounts of fat tissue will exhibit a high phase angle. Water retention can lead to low phase angle values. The BIVA and the phase angle are the essential parameters in this example for identifying water retentions,  that result from an illness and that lead to weight gain.

Both parameters can also offer essential information about tumor patients’ body compositions. A precise estimation of this patient group’s nutrition status plays a vital role for prognosis and further therapy procedures. Cancer patients can suffer from the so called tumor cachexia, which is a multifactorial syndrome that is distinguished by unwanted weight loss, a loss of muscular mass, tiredness and weakness, as well as visibly reduced appetite. By way of the
seca mBCA, the development of a tumor cachexia can be recognised early on. Especially during the early stages of this development, the BMI and fat mass can remain within normal range despite obvious weight loss.

In our case example, the tumor patient even shows a slight increase in BMI and fat mass after the first signs of weight loss. The BCC, on the other hand, shows a decrease of fat free mass and the BIVA serves for identifying the cause – a visible cell loss, which is situated outside of the 95% tolerance ellipse. This information, paired with a decreased phase angle can distinctly point to a relevant loss of muscular mass. Even though the BMI and fat mass are still within normal range, the loss of muscular mass indicates a tumor cachexia for this patient. For further case studies on diagnosing diseases with the seca mBCA, click here.

By combining the bioelectrical impedance analysis, the BIVA and the analysis of the phase angle, the seca mBCA is a precise instrument with a wide range of possible applications in medicine. Measuring results of the seca mBCA have been validated towards the according gold standards and display the highest levels of reliability and reproducibility. In only one measuring procedure, body composition, water supply and cell status can be quickly and easily determined. Results can be printed as a comprehensive document for patients, offering the patient and the doctor all important information. Additionally, the data can be transmitted into a patient data management system (PDMS).

If you are personally interested in finding out more about the advantages of a seca mBCA device, seca offers product demonstrations free of charge. For inquiries and further information, please click here.

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