A method for analyzing a cause of prolonging a coagulation time of a blood specimen from a subject, without using a specimen obtained by mixing of the blood specimen from the subject and a normal blood specimen, the method comprising: adding a calcium solution to a first sample resulting from an elapse of a first waiting time from mixing of the blood specimen from the subject and a measurement reagent for an activated partial thromboplastin time; obtaining a first coagulation time and/or a first parameter regarding a differential of a coagulation waveform, for the first sample to which the calcium solution has been added; adding the calcium solution to a second sample resulting from an elapse of a second waiting time, which is longer than the first waiting time, from mixing of the blood specimen from the subject and the measurement reagent; obtaining a second coagulation time and/or a second parameter regarding a differential of a coagulation waveform, for the second sample to which the calcium solution has been added; and obtaining information regarding a cause of prolonging a coagulation time, on the basis of the first coagulation time and/or the first parameter and the second coagulation time and/or the second parameter, wherein the obtaining of the information comprises obtaining an index value based on the first coagulation time and/or the first parameter and the second coagulation time and/or the second parameter, and obtaining the information on the basis of a result of comparison between the index value and a predetermined threshold value, and wherein the information is related to a suspicion that the blood specimen contains lupus anticoagulant when the result of comparison matches a predetermined condition; or the information is related to a suspicion that the blood specimen contains heparin when the result of comparison matches a predetermined condition; or the information is related to a suspicion that the blood specimen contains lupus anticoagulant or heparin when the result of comparison matches a predetermined condition. adding a calcium solution to a first sample resulting from an elapse of a first waiting time from mixing of the blood specimen from the subject and a measurement reagent for an activated partial thromboplastin time; obtaining a first coagulation time and/or a first parameter regarding a differential of a coagulation waveform, for the first sample to which the calcium solution has been added; adding the calcium solution to a second sample resulting from an elapse of a second waiting time, which is longer than the first waiting time, from mixing of the blood specimen from the subject and the measurement reagent; obtaining a second coagulation time and/or a second parameter regarding a differential of a coagulation waveform, for the second sample to which the calcium solution has been added; and obtaining information regarding a cause of prolonging a coagulation time, on the basis of the first coagulation time and/or the first parameter and the second coagulation time and/or the second parameter, wherein the obtaining of the information comprises obtaining an index value based on the first coagulation time and/or the first parameter and the second coagulation time and/or the second parameter, and obtaining the information on the basis of a result of comparison between the index value and a predetermined threshold value, and wherein obtaining an index value based on the first coagulation time and/or the first parameter and the second coagulation time and/or the second parameter, and obtaining the information on the basis of a result of comparison between the index value and a predetermined threshold value, and wherein the information is related to a suspicion that the blood specimen contains lupus anticoagulant when the result of comparison matches a predetermined condition; or the information is related to a suspicion that the blood specimen contains heparin when the result of comparison matches a predetermined condition; or the information is related to a suspicion that the blood specimen contains lupus anticoagulant or heparin when the result of comparison matches a predetermined condition.