Abstract:
Disclosed is a urine specimen analyzing method which improves the detection of casts in a urine specimen by flowing a measurement sample containing a urine specimen through a flow cell, irradiating light on the measurement sample flowing through the flow cell, generating a signal waveform indicating a temporal change of intensity of light given off by the measurement sample, and detecting casts distinguishably from mucus threads contained in the urine specimen, based on information related to respective slope at both end sides of the signal waveform corresponding to each formed element contained in the urine specimen.

Description:
RELATED APPLICATIONS 
     This application claims priority from prior Japanese Patent Application No. 2014-071950, filed on Mar. 31, 2014, entitled “URINE SPECIMEN ANALYZING METHOD AND URINE ANALYZER”, the entire contents of which are incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a urine analyzing method, a urine analyzer and a non-transitory computer-readable storage medium. 
     2. Description of the Related Art 
     There are conventional urine sample analyzers which detect and count formed elements contained in urine. Casts and mucus threads are among the formed elements contained in urine. It is known that counting casts and mucus threads contained in urine has clinical significance. Mucus threads are long and narrow and have a shape similar to that of casts. Therefore, mucus threads produce noise when detecting casts. 
     U.S. Pat. No. 5,719,666 discloses discriminating between casts and mucus threads based on the (volume)/(length) of the detected formed element. 
     There is demand for more accurate identification of casts and mucus threads. 
     SUMMARY OF THE INVENTION 
     The scope of the invention is defined by the appended claims, and not by any statements within this summary. 
     A first aspect of the present invention relates to a urine specimen analyzing method. The method comprises: flowing a measurement sample containing a urine specimen through a flow cell; irradiating light on the measurement sample flowing through the flow cell; generating a signal waveform indicating a temporal change of intensity of light given off by the measurement sample; and detecting casts distinguishably from mucus threads contained in the urine specimen, based on information related to respective slope at both end sides of the signal waveform corresponding to each formed element contained in the urine specimen. 
     A second aspect of the present invention relates to a urine analyzer. The analyzer comprises: a flow cell through which a measurement sample containing a urine specimen flows; a light source arranged at a position for irradiating light on the measurement sample flowing through the flow cell; a light receiving part configured to generate a signal waveform indicating a temporal change of an intensity of light given off by the measurement sample; and a processing part configured to detect casts distinguishably from mucus threads contained in the urine specimen, based on information related to respective slope at both end sides of the signal waveform corresponding to each formed element contained in the urine specimen. 
     A third aspect of the present invention relates to a non-transitory computer-readable storage medium storing a program. The program causes a processor connected to an optical detector to execute operations comprising: instructing the optical detector to flow a measurement sample containing a urine specimen through a flow cell; instructing the optical detector to irradiate light on the measurement sample flowing through the flow cell; receiving, from the optical detector, a signal waveform indicating a temporal change of intensity of light given off by the measurement sample; and detecting casts distinguishably from mucus threads contained in the urine specimen, based on information related to respective slope at both end sides of the signal waveform corresponding to each formed element contained in the urine specimen. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a brief block diagram of the urine sample analyzer of a first embodiment; 
         FIG. 2  is a schematic view of the urine sample distributing part and a measurement sample preparation part; 
         FIG. 3  is a schematic view of an optical detection part; 
         FIG. 4  is a flow chart of the urine sample analysis operation in the first embodiment; 
         FIG. 5  is an example of a signal waveform on a time axis from a cast; 
         FIG. 6  is an example of a signal waveform on a time axis from a mucus thread; 
         FIG. 7  is a graph representing the regions specifying the formed elements as cast or mucus thread in the first embodiment: 
         FIG. 8  is a graph representing the regions specifying the formed elements as cast or mucus thread in a second embodiment; 
         FIG. 9  is a schematic view showing an example a plurality of entangled mucus threads with other adhered impurities; 
         FIG. 10  shows an example of a signal waveform of a clot of plurality of entangled mucus threads with other adhered impurities; 
         FIG. 11  shows an example of a signal waveform of a clot of a plurality of entangled mucus threads with other adhered impurities; 
         FIG. 12  shows an example of a signal waveform of a clot of a plurality of entangled mucus threads with other adhered impurities; 
         FIG. 13  shows an example of a signal waveform of a clot of a plurality of entangled mucus threads with other adhered impurities; 
         FIG. 14  is an example of a signal waveform on a time axis from a cast; and 
         FIG. 15  is an example of a signal waveform on a time axis from a cast. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments of the present invention are described hereinafter. Note that the following embodiments are merely illustrative. Note also that the present invention is not limited to the following embodiments. 
     First Embodiment 
     (Urine Sample Analyzer  1 ) 
       FIG. 1  is a brief block diagram of the urine sample analyzer  1  of a first embodiment. The urine sample analyzer  1  shown in  FIG. 1  analyzes the formed elements in urine samples. Formed elements in urine samples include red blood cells, white blood cells, epithelial cells, bacteria, casts, and mucus threads. Casts are result of, for example, Tamm-Horsfall mucoprotein coagulating sedimentation in the renal tubular lumen. Blood cells and renal tubular epithelial cells are sometimes included in the substrate of the cast. Mucus threads include mucoprotein, and are long and thin formed elements. 
     The urine sample analyzer  1  has a urine sample distribution part  10 , sample preparation part  20 , optical detection unit  30 , and processing part  40 . 
       FIG. 2  is a schematic view of the urine sample distribution part  10  and the sample preparation part  20 . As shown in  FIG. 2 , the urine sample distribution part  10  aspirates a predetermined amount of urine sample accommodated in a test tube  12  using an aspirating tube  11 . The urine sample distribution part  10  dispenses the aspirated sample to the sample preparation part  20 . Specifically, the urine sample distribution part  10  allocates urine sample aliquot to a first reaction tank  21   a  and a second reaction tank  21   b  of the sample preparation part  20 . 
     In the first reaction tank  21   a , the aliquot is mixed with a first diluting liquid  22   a  and a first staining liquid  23   a . Hence, the formed elements in the measurement sample are stained by the colorant contained in the first staining liquid  23   a . The first staining liquid  23   a  contains a staining dye which stains the cell membrane and proteins. A first measurement sample prepared in the first reaction tank  21   a  is supplied for analysis of particles that do not have nucleic acid, such as red blood cells, casts, mucus threads and the like, in urine. 
     In the second reaction tank  21   b , the aliquot is mixed with a second diluting liquid  22   b  and a second staining liquid  23   b . Hence, the formed elements in the measurement sample are stained by the colorant contained in the second staining liquid  23   b . The second staining liquid  23   b  contains a staining dye which specifically stains nucleic acid. A second measurement sample prepared in the second reaction tank  21   b  is supplied for analysis of particles that have nucleic acid, such as white blood cells, epithelial cells, fungi, bacteria and the like, in urine. 
     The first and second reactor tanks  21   a  and  21   b  are respectively connected to the flow cell  31  of the optical detection unit  30 . The first and second measurement samples are supplied from the first and second reaction tanks  21   a  and  21   b  to the flow cell  31 . The measurement samples pass through the center of a pressurized sheath fluid flowing within the flow cell  31 . A layered sheath flow is formed by the sheath fluid at this time. The formed elements contained in the measurement sample are drawn one by one into the layered sheath flow. The formed elements in the measurement sample pass through within the flow cell  31  one by one. 
       FIG. 3  is a schematic view of the optical detection part  30 . As shown in  FIG. 3 , the optical detection part  30  has a light source  32 . The light source  32  is configured by, for example, a semiconductor laser, gas laser or the like. The light from the light source  32  is condensed on the measurement sample flowing through the flow cell  31  via a condensing optical system  33 . In this way the forward scattered light, side scattered light, and fluorescent light are given off from the formed elements contained in the measurement sample. 
     The forward scattered light is condensed on the light receiving part  35  of the optical system  34 . The light receiving part  35  generates a forward scattered light signal (FSC) corresponding to the intensity of the received forward scattered light. The light receiving part  35  may be configured by, for example, a photodiode or the like. 
     The side scattered light is condensed on the light receiving part  38  by way of optical system  36  and dichroic mirror  37 . The light receiving part  38  generates a side scattered light signal (SSC) corresponding to the intensity of the received side scattered light. The light receiving part  38  may be configured by, for example, a photomultiplier or the like. 
     The fluorescent light is condensed on the light receiving part  39  by way of optical system  36  and dichroic mirror  37 . The light receiving part  39  generates a fluorescent light signal (FL) corresponding to the intensity of the received fluorescent light. The light receiving part  39  may be configured by, for example, a photomultiplier or the like. 
     The forward scattered light signal (FSC), side scattered light signal (SSC), and fluorescent light signal (FL) are respectively output to a processing part  40 . The processing part  40  counts each of the formed elements using the forward scattered light signal (FSC), side scattered light signal (SSC), and fluorescent light signal (FL). The processing part  40  controls the urine sample distribution part  10 , sample preparation part  20 , and optical detection part  30 . The processing part  40  includes a hard disc (memory) storing control programs for performing the control and analysis programs for identifying types of the formed elements, a CPU executing the programs read out from the hard disc, and so on. 
     (Urine Sample Analyzing Method Used in Urine Sample Analyzer  1 ) 
     In urine sample analyzer  1 , the processing part  40  first controls the urine sample distribution part  10  and the sample preparation part  20  to prepare a measurement sample. Specifically, the processing part  40  controls the urine sample distribution part  10  to aspirate a sample (step S 1 ), and controls the sample preparation part  20  to prepare a measurement samples from the aspirated sample, diluting liquids  22   a  and  22   b , and staining liquids  23   a  and  23   b  (step S 2 ), as shown in  FIG. 4 . As a result, a first measurement sample is prepared by mixing the first diluting liquid  22   a  and first staining liquid  23   a  with the urine sample, and a second measurement sample is prepared by mixing the second diluting liquid  22   b  and the second staining liquid  23   b  with the urine sample. 
     The processing part  40  then controls the optical detection part  30  to measure pursuant with the measurement items (step S 3 ). The first measurement sample is supplied to the flow cell  31  while the sheath fluid is fed to the flow cell  31 . The optical detection part  30  detects the forward scattered light, side scattered light, and fluorescent light, and generates forward scattered light signals (FSC), side scattered light signals (SSC), and fluorescent light signals (FL). The forward scattered light signal (FSC), side scattered light signal (SSC), and fluorescent light signal (FL) are respectively output to the processing part  40 . 
     The second measurement sample is then supplied to the flow cell  31  while the sheath fluid is fed to the flow cell  31 . The optical detection part  30  detects the forward scattered light, side scattered light, and fluorescent light, and generates forward scattered light signals (FSC), side scattered light signals (SSC), and fluorescent light signals (FL) according to the intensity of the light. The forward scattered light signal (FSC), side scattered light signal (SSC), and fluorescent light signal (FL) are respectively output to the processing part  40 . 
     The processing part  40  analyzes the output signals (step S 4 ). Specifically, the processing part  40  counts the formed elements such as red blood cells, white blood cells, epithelial cells, bacteria, casts, and mucus threads. The processing part  40  subsequently shows the analysis results on a display part which is not shown in the drawing (step S 5 ). 
     The present embodiment is described in terms elan example in which the processing part  40  counts casts and mucus threads based on the fluorescent light signal (FL). However, the present invention is not limited to this example. The processing part  40  also may be configured to specify formed elements using a signal other than the fluorescent light signal (FL). For example, the processing part  40  also may be configured to specify formed elements using signals related to the intensity of scattered light such as forward scattered light and side scattered light. 
       FIG. 5  is an example of a signal waveform on a time axis from a cast. The signal waveform indicates a temporal change of signal intensity obtained from the cast. Casts are generally thick, and have a uniform thickness. Therefore, casts have a large slope at both end s of the signal waveform on the time axis. That is, the bilateral ends are steep on the signal waveform on the time axis in the case of casts. 
       FIG. 6  is an example of a signal waveform on a time axis from a mucus thread. The signal waveform indicates a temporal change of signal intensity obtained from the mucus thread. Mucus threads generally are thinner than casts, and have a narrow shape tapering from at least one end among a leading end and a trailing end. Therefore, mucus threads have a small slope at least at one end of the signal waveform on the time axis. Mucus threads also may have a steep slope at least at one end of the signal waveform on the time axis.  FIG. 6  shows an example of the small slope at the leading end of the signal waveform of a mucus thread. The mucus thread signal waveform on a time axis includes signal waveforms which have a small slope at the trailing end, and signal waveforms which have a small slope at both the leading end and the trailing end. 
     Note that in the present specification the term “leading end” is defined as the downstream side of the flow cell  31  in the direction of the flow. Note also that in the present specification the term “trailing end” is defined as the upstream side of the flow cell  31  in the direction of flow. 
     In view of the characteristics of the signal waveform on the time axis corresponding to casts and mucus threads as described above, the processing part  40  of the urine analyzer  1  identifies the type of the formed element based on information related to the slope at least at one end of the signal waveform on the time axis corresponding to each formed element. Specifically, the processing part  40  determines that a formed element corresponding to a signal waveform having bilateral slopes that are smaller than a slope threshold value is a mucus thread based on information related to the slopes at bilateral ends of the signal waveform. The cast signal waveform does not satisfy the condition that at least the slope at one end is smaller than a slope threshold value. Therefore, the processing part  40  determines that a formed element corresponding to a signal waveform having bilateral slopes that are greater than a slope threshold value is a cast based on information related to the slopes at bilateral ends of the signal waveform. In this way casts and mucus threads contained in a urine sample can be discriminated with high degree of accuracy. 
     More specifically, the processing part  40  uses the time Ta from when the signal waveform initially attains the first signal level Th 1  (refer to  FIGS. 5 and 6 ) to the second signal level Th 2  which is higher than the first signal level Th 1 , and the time Tb from when the signal waveform finally falls from the second signal level Th 2  to the first signal level Th 1  as information related to the slope of the ends of the signal waveform. The time Ta is a parameter representing the steepness of the slope at the leading end of the signal waveform. The time Tb is a parameter representing the steepness of the slope at the trailing end of the signal waveform. 
     As shown in  FIG. 7 , the processing part  40  identifies a formed element as mucus thread when at least one of these conditions is satisfied: the time Ta is greater than a predetermined time Ta 1 , and a time Tb is greater than a predetermined time Tb 1 . That is, the processing part  40  identifies a formed element as a mucus thread when the condition Ta&gt;Ta 1  and Tb&gt;Tb 1  is satisfied, when Ta&gt;Ta 1  and Tb≦Tb 1  is satisfied, and when Ta≦Ta 1  and Tb&gt;Tb 1  is satisfied. The processing part  40  identifies a formed element as a cast when the condition Ta≦Ta 1  and Tb≦Tb 1  is satisfied. 
     Thus, the casts and mucus threads contained in the urine specimen are discriminated and detected based on information related to the respective slope at both ends of the waveform of the signal corresponding to each formed element contained in the urine specimen. Casts contained in a urine sample therefore are discriminated to a high degree. 
     Note that the first signal level Th 1  may be, for example, approximately 3 to 10% of the maximum signal intensity. Further note that the second signal level Th 2  may be, for example, approximately 50 to 80% of the maximum signal intensity. 
     Second Embodiment 
     The first embodiment is described by way of example in which formed element is identified as a cast when the conditions Ta≦Ta 1  and Tb≦Tb 1  are satisfied. However, there may be times when all formed elements which have signal waveforms contained in this region cannot be identified as casts. For example, consider cases in which a plurality of mucus threads are entangled and form a single clot, and in which an impurity such as another cell is adhered to a mucus thread. In such cases there is a possibility that the conditions Ta≦Ta 1  and Tb≦Tb 1  may be satisfied even when the signal waveform is that of a mucus thread. In view of this possibility, the second embodiment also the possibility of a cast and the possibility of a mucus thread when the conditions Ta≦Ta 1  and Tb≦Tb 1  are satisfied, as shown in  FIG. 8 . Specifically, in this embodiment mucus threads contained in a urine sample are discriminated, and casts are detected based on information related to the respective slop at bilateral ends of the signal waveform, and information reflecting the shape of the part of the waveform which is not at either end of the signal waveform. In this way casts can be discriminated from mucus threads and detected with high identification accuracy. Note that the information reflecting the shape of the part of the waveform which is not at either end of the signal waveform also may be a parameter representing the correlation between the width of the signal waveform and the area of the signal waveform. 
     When, for example, impurities are adhered to both ends of a clot of a plurality of mutually entangled mucus threads as shown in  FIG. 9 , the signal waveform is steep at the bilateral ends of the waveform and the conditions Ta≦Ta 1  and Tb≦Tb 1  are satisfied. However, it is difficult to hypothesize that impurities are adhered to the entire mucus thread even in such cases. Therefore, clots that have a plurality of mucus threads generally have a part which is narrower than another part. In view of this possibility, a formed element is identified as a mucus thread when there is no predetermined correlation between the width Tw of the signal waveform and the area S of the signal waveform even when the respective slopes at the bilateral ends of the signal waveform are smaller than the slope threshold value. Hence, the processing part  40  identifies a formed element as a cast when the slopes at the respective bilateral ends of the signal waveform are less than the slope threshold value and there is a predetermined correlation between the width Tw of the signal waveform and the area S of the signal waveform. 
     That is, the processing part  40  identifies a formed element as a mucus thread when the condition Ta&gt;Ta 1  and Tb&gt;Tb 1  is satisfied, when the condition Ta&gt;Ta 1  and Tb≦Tb 1  is satisfied, when the condition Ta≦Ta 1  and Tb&gt;Tb 1  is satisfied, and when the condition Ta≦Ta 1  and Tb≦Tb 1  and there is no predetermined correlation between width Tw and area S is satisfied. The processing part  40  identifies a formed element as a cast when the condition Ta≦Ta 1  and Tb≦Tb 1  and there is a predetermined correlation between the width Tw and the area S is satisfied. Accordingly, the urine sample analyzer  1  identifies mucus threads and casts with higher accuracy. 
     Note that “width of the signal waveform” is the period from when the signal waveform initially attains the second signal level Th 2  to when the signal waveform finally falls from the second signal level Th 2 , as shown in  FIG. 10 . 
     The area S is the area of the region (the hatch-marked region in  FIG. 10 ) circumscribed by signal waveform and the straight line representing the signal intensity=0 in the period between when the signal waveform initially attains second signal level Th 2  to when the signal waveform finally falls from the second signal level Th 2 . 
     The value R representing the correlation between the signal waveform width Tw and the signal waveform area S can be expressed as, for example, R=S/(Tw×h). Where h is a constant. The constant h is preferably the height of the second signal level Th 2 . The denominator (Tw×h) is equal to the area of the rectangle having the width Tw of the period from when the signal level initially exceeds the second signal level Th 2  to when the signal level finally falls below the second signal level Th 2 , and a height Th 2 . That is, the denominator (Tw×h) is equal to the area S 2  represented by the hatch marks of  FIG. 5 . Therefore, the equation can be expressed as R=S/S 2 . 
     In a clot formed by a plurality of mutually entangled mucus threads, a thin part readily occurs in the middle part in the length direction, as described above. In the case of casts, however, a thin part is unlikely to occur in the middle part in the length direction. Therefore, the area S will be small in the case of a mucus thread, and large in the case of a cast. The value R obtained by dividing the area S by the area S 2  is a value approaching 1 in the case of casts, and a value less than 1 in the case of mucus threads. 
     Therefore, mucus threads and casts can be identified with high accuracy by comparing the threshold value R 1  with the value R, which represents the correlation between the width Tw and the area S. 
     The threshold value R 1  is preferably set, for example, at approximately 0.7. That is, when the area S 1  is less than 70% of area S 2 , the formed element is preferably identified as mucus thread. 
     Other Embodiment 
     The value R which represents the correlation between the signal waveform width Tw and the signal waveform area S in the second embodiment also may be the ratio R 2  of the signal waveform Tw and the signal waveform area S. For example, the ratio R 2  also may be expressed as S/Tw. In this case, the ratio R 2  is the maximum value Rmax when the signal level does not once fall below Th 2  in the part that is not at the bilateral ends of the signal waveform, as shown in  FIG. 5 . Mucus threads and casts can be identified with high accuracy by comparing the ratio R 2  and a threshold value R 1  The threshold value R 3  may be approximately 70% of the maximum value Rmax. 
     The signal waveform width Tw in the second embodiment, for example, also may be the period from when the signal waveform initially exceeds the signal level Th 1  to when the signal waveform finally falls below the first signal level Th 1 . In this case, the area S of the signal waveform may be the area S 1  of the region (the hatch-marked part in  FIG. 12 ) in the period. 
     The second embodiment is described by way of example using a parameter representing the correlation between the signal waveform width Tw and the signal waveform area S to determine whether formed elements having a signal waveform which satisfies the condition Ta≦Ta 1  and Tb≦Tb 1  are casts or mucus threads. However, the present invention is not limited to this example. Other parameters also may be used as the information reflecting the shape of the part of the signal waveform which is not part of the bilateral ends of the signal waveform. 
     For example, information reflecting the thinness of the part which is thinner than the bilateral ends in the formed element may be used as another parameter. 
     The processing part  40  also may be configured to identify a formed element as a mucus thread when the slope at the bilateral ends of the signal waveform are respectively greater than a threshold value of the slope, and minimum value of the signal waveform is less than the threshold value of the signal waveform. 
     Referring to  FIG. 11 , for example, the processing part  40  also may be configured to identify a formed element as a mucus thread when the minimum value Ts of the signal waveform is less than a third signal level Th 3 . In this case the third signal level Th 3  is preferably greater than the first signal level Th 1 , but less than the second signal level Th 2 . The third signal level Th 3  is preferably, for example, approximately 20 to 30% of the maximum signal intensity. 
     For example, the minimum value may be the signal level when the signal level is lowest on the period from when the second signal level Th 2  is initially exceeds to when the signal level finally falls below the second signal level Th 2 . 
     The processing part  40  also may be configured to identify a formed element as a cast when the slope at the bilateral ends of the signal waveform are respectively greater than a threshold value of the slope, and minimum value of the signal waveform is greater than the threshold value of the signal waveform. 
     For example, the processing part  40  also may be configured to identify a formed element as a casts when the condition Ta≦Ta 1  and Tb≦Tb 1  is satisfied and the minimum value Ts of the signal waveform is greater than the third signal level Th 3 . 
     In a clot formed by a plurality of mutually entangled mucus threads, a thin part readily occurs in the middle part in the length direction, as described above. The minimum value Ts reflects the thinness of the thin part in the middle part of the formed element. Accordingly, mucus threads and casts can be identified with high accuracy by determining the height of the minimum value Ts of the signal waveform relative to the third signal level Th 3 . 
     Note that the threshold value (Th 3 ) relative to the minimum value Ts is not necessarily a fixed value. The threshold value (Th 3 ) relative to the minimum value Ts also may be a variable value determined according to the signal waveform. For example, a specific value within a range of 10 to 20% of the maximum value of the waveform signal level may be used as the threshold value relative to the minimum value Ts. 
     The rate of reduction of the signal level in the part not at the bilateral ends also may be used instead of the minimum value as the information reflecting the thinness of the part which is thinner than the bilateral ends of the formed element. For example, the rate of reduction may represent the ratio of the minimum value Is determined as described above, and the maximum value of the signal level of the waveform. 
     The processing part  40  also may be configured to identify a formed element as a mucus thread when the slope of the respective bilateral ends of the signal waveform are greater than the slope threshold value, and the sum of the width of the part positioned in the period from when one signal level initially exceeds a threshold value to when one signal level finally falls, and the width of the part in which the signal level which has a signal level greater than one signal level is less than a threshold value, and this sum exceeds a threshold value. 
     For example, referring to  FIG. 13 , the processing part  40  also may be configured to identify a formed element as a mucus thread when the sum Td, of the widths Td 1  and Td 2  of the parts positioned in the period from when the signal waveform initially exceeds the first signal level Th 1  to when the signal waveform finally falls below the first signal level Th 1  and is less than the third signal level Th 3 , is greater than the threshold value Tw 1 . 
     The processing part  40  also may be configured to identify a formed element as a cast when the slope of the respective bilateral ends of the signal waveform is greater than a slope threshold value, and the sum of the widths of the parts, positioned in the period among the waveforms from when the signal waveform initially exceeds one signal level to when the signal waveform finally falls below one signal level and the part is less than another signal level, is greater than a threshold value. 
     For example, the processing part  40  also may be configured to identify a formed element as a cast when the sum Td, of the widths Td 1  and Td 2  of the parts positioned in the period from when the signal waveform initially exceeds the first signal level Th 1  to when the signal waveform finally falls below the first signal level Th 1  and is less than the third signal level Th 3 , is less than the threshold value Tw 1 . 
     In a clot formed by a plurality of mutually entangled mucus threads, a thin part readily occurs in the middle part in the length direction, as described above. In the case of casts, however, a thin part is unlikely to occur in the middle part in the length direction. Therefore, the sum Td of the widths is larger in the case of mucus threads, and smaller in the case of casts. Therefore, mucus threads and casts can be identified with high accuracy by comparing the sum Td of the widths and the threshold value Tw 1 . 
     For example, the threshold value Tw 1  preferably is approximately 30% of the width Tw (the period from when the waveform signal initially exceeds Th 2  to when the signal finally falls below Th 2 ) of the waveform signal. 
     The second embodiment is described by way of example using times Ta and Tb as the information related to the slope. In the present invention, other information also may be used as information related to slope. 
     For example, referring to  FIG. 14 , the area of a triangle circumscribed by a first intersection point, a second intersection point, and a third intersection point also may be used as information related to slope when the intersection of the signal waveform and the first signal level Th 1  is designated the first intersection point, the intersection of the signal waveform and the second signal level Th 2  is designated the second intersection point, and the intersection of the first signal level Th 1  and the time positioned at the second intersection point is designated the third intersection point. 
     For example, referring to  FIG. 15 , the area of regions A 1  and A 2 , which are circumscribed by time Tz 1  and time Tz 2  which are located at the intersection points C 4  of the signal waveform and the first signal level Th 1 , and the signal waveform and the second signal Th 2 , also may be used as the information related to slope.