The present invention relates to a strip for an improved lateral flow assay of a biological sample on a single plane and a lateral flow chromatography assay using a test device containing the same. The strip of the present invention consists of a single-pad, which can improve lateral flow assay by providing an easy and simple procedure and clear visual reading. The strip of the present invention is consisted of sample application (sample) zone and reactant-resultant zone where the reaction mixture is deposited (reactant) are all on a same plane. In addition, the present invention provides a chromatographic method wherein hemoglobin is separated from analyte by a differential chromatography on the solid phase. Any interference of detection of the result by hemoglobin is removed by the present invention. The present invention provides advantages including an easy and simple procedure with a quick and clear response.