Many patients will have occult blood/ occult blood + when they do urine routine, they will suspect whether they are suffering from incurable diseases like nephritis/urea, and clinicians do not have much time to explain to patients in detail due to their busy schedule, which causes great distress to patients, today I will give you a brief introduction to the relationship between occult blood and nephritis. Positive occult blood ≠ hematuria The occult blood in urine routine is to detect hemoglobin (the main component of red blood cells in blood), but it also reacts to many other substances, such as oxidants and bacteria, thus mistaking it for the presence of red blood cells in urine, which is medically called a false positive. In contrast, true hematuria is defined as a number of red blood cells per high-powered field of view >3 (>3/HP) in red blood cell microscopy. Hematuria ≠ nephritis Many causes can lead to hematuria, and nephritis is only one of them. The common causes of hematuria are divided into two categories: physiological and pathological. 1.Physiological hematuria For example, fever and strenuous exercise can cause hematuria, which is usually transient. 2, pathological hematuria Various diseases can lead to hematuria, common are urinary system diseases, such as urinary tract infection, stones, tumors, nephritis is also a common cause. Systemic diseases, such as sepsis, leukemia, purpura. Immune system diseases, such as systemic lupus erythematosus, rheumatoid arthritis, etc. Certain drugs can also cause hematuria, such as sulfonamides, indomethacin, warfarin, cyclophosphamide, heavy metal ions, etc. How to identify hematuria caused by nephritis Hematuria caused by nephritis is usually dominated by anisocytic red blood cells, and morphological examination of urinary red blood cell phase difference is needed. If anisocytic red blood cells > 80%, or spiny red blood cells > 5%, consider nephritis as a high possibility, and vice versa, consider other causes of hematuria.