A cell volume greater than 40% on TCT is a good indication of satisfactory sampling and satisfactory specimen. If the cell volume is less than 40%, it indicates that the sampling is not satisfactory, which may sometimes result in a missed diagnosis. There are two possible reasons for a low cell volume: first, incorrect method of sampling.1. Failure to spread the brush flat on the surface of the squamocolumnar junction.2. Incorrect timing of sampling or method of sampling. The second, which may occur in the type III transformation zone, is that the squamocolumnar junction retracts into the cervical canal, which may result in a low cell volume, and may easily lead to a missed diagnosis. Periodic review is recommended in the presence of this phenomenon.