I. INTRODUCTION

　　I N RECENT years， bioelectrical impedance analysis （BIA） has become an increasingly popular modality in the assessment of human body composition： bioelectrical tissue conductivity， mass distribution and water compartments. BIA technique， which measures the whole body bioimpedance， provides a noninvasive and practical method to estimate body composition and body hydration in human ［1］–［6］。 Since then， this technique is widely used in human nutrition and clinical research.

　　BIA has shown to be sensitive in determining the hydrational profile in dengue patients ［7］–［9］。 However， BIA did not improve on serial hematocrit and bodyweight determinations for Manuscript received June 2， 2003; revised September 1， 2004. The work of F. Ibrahim was supported by the University of Malaya and the Sultan Iskandar Johor Foundation. F. Ibrahim and W. A. B. Wan Abas are with the Department of Biomedical Engineering， University of Malaya， 50603 Kuala Lumpur， Malaysia. M. N. Taib is with the Universiti of Teknologi MARA， 40450 Shah Alam， Shah Alam， Selangor， Malaysia. C. H. Guan is with the Department of Cardiology， Hostpital Pantai Putri Ipoh， 31400 Ipoh， Perak， Malaysia. S. Sulaiman is with the Damansara Specialist Hospital， 47400 Petaling Jaya， Selangor， Malaysia. Digital Object Identifier 10.1109/TIM.2004.840237 monitoring plasma volume contraction and extracellular expansion in dengue patients， respectively ［10］。 Recent studies on BIA indicate body composition， as reflected by reactance， greatly in- fluence the assessment of hematocrit status and modeling of hemoglobin in dengue hemorrhagic fever ［11］， ［12］。

　　Dengue fever （DF） is an acute febrile viral disease frequently presented with headache， bone or joint and muscular pains， and rash. A significant percentage of DF patients develop a more severe form of disease， known as dengue hemorrhagic fever （DHF）。 DHF is an infection associated with an increase in microvascular permeability， a decrease in plasma volume， and in severe forms hypotension and shock ［13］。 Measurement of total increase in hematocrit （Hct） （over 20%） or hemoglobin （Hb） concentration （Hb above the upper normal range limit） is one of the method for monitoring the onset and progression of plasma leakage ［13］。 Another conventional method for monitoring risk in DHF patients is to monitor their platelet count and liver function status ［13］， ［14］。 These techniques are invasive， tedious， and time-consuming. Moreover， frequent blood taking will cause further injury to the subcutaneous tissue and potentially risky to the DHF patients.