Phase angle measurement in pulmonary tuberculosis patients and control subjects using bio-impedance analysis

Bio-impedance is the measure of impedance of the body. Impedance consists of resistance and reactance. Phase angle (PA) is the tan value of the ratio of reactance versus resistance. PA depends on cell membrane integrity and on body cell mass. Earlier studies have shown a correlation between PA values and body cell mass. Body cell mass varies in chronic diseases like HIV infection, tuberculosis, cancers and chronic renal failure.

The aim of this study was to compare the PA values of tuberculosis patients (TB) with that of control subjects and to compare the anthropometric values between the groups.

Bioimpedance analysis and PA measurements were done using Bodystat Quadscan 4000 machine on 30 tuberculosis patients and controls between the age group of 18 to 50 years.

The PA values were 5.09 +/- 1.11 degrees and 7.2 +/- 1.27 degrees in TB patients and control subjects respectively. PA values were positively correlated with Body mass index (BMI) in TB patients and control (r = 0.42 and 0.011, both p < 0.001). Mean difference and its 95% confidence interval between groups for PA were -2.11 (-2.72, -1.49), for weight -13.9 (-18.1, -9.7), for BMI -5.65 (-7.1, -4.2), for corrected arm muscle area (CAMA) -9.91 (-13.2, -6.6) and for impedance 152.6 (106.6, 198.6). PA, weight, BMI and CAMA were significantly higher in control subjects and impedance was lower in control groups using independent sample t test.

PA and nutritional status were significantly low in TB patients as compared with control subjects.