Clinically, if a patient has the symptoms of diabetes mellitus, such as excessive drinking, excessive urination, and excessive eating with weight loss, it often indicates the possibility of elevated blood glucose, but not necessarily diabetes mellitus, and the monitoring of venous plasma and blood glucose needs to be improved. If it is accompanied by venous plasma fasting glucose ≥7.0mmol/L, diabetes can be diagnosed, but if the monitored venous plasma fasting glucose is normal level, diabetes can be excluded. Therefore, the clinical symptoms of diabetes mellitus may not necessarily be diabetes mellitus, but also other diseases such as hyperthyroidism, which may be manifested as polyphagia, lethargy, diarrhea and panic, and some patients have symptoms such as polydipsia and polyuria, and monitoring of thyroid function indicates the presence of hyperthyroidism. The above symptoms can be improved after the hyperthyroidism is cured, and the blood sugar of some patients can be restored to normal. Therefore, the clinical symptoms of diabetes mellitus with three more and one less only indicate the possibility of elevated blood sugar, but not necessarily diabetes mellitus.