Urinary tract infections are those in which bacteria have invaded the body’s urethra, bladder, ureters and kidneys and caused inflammation. To diagnose a urinary tract infection, it is important to first clarify the site of infection, whether it is infecting the kidneys (commonly known as the upper urinary tract) or the urethra or bladder, the latter also known as the lower urinary tract; because the treatment time, medications used and the impact on the patient’s health are completely different between the two. In the case of pyelonephritis, long-term, recurrent attacks may cause decreased kidney function, which may then develop into uremia. Lower urinary tract infections, on the other hand, do not. Clinically, when you have a urinary tract infection, you will usually experience frequent urination, urgency, painful urination, difficulty urinating, or lower abdominal distension. Lower urinary tract infections are usually considered in patients who present this way; however, this is not always the case. Studies have shown that 30% of patients who present with symptoms of lower urinary tract infections actually have pyelonephritis. What are the manifestations of pyelonephritis? In addition to the symptoms mentioned earlier, patients may have symptoms such as chills, high fever, back pain, general weakness, and percussion pain in the kidney area on physical examination. Laboratory tests show elevated routine blood leukocytes, urine routine leukocytes greater than 5 per high-powered view, and in severe cases urine leukocytes greater than 100; urine culture may show growth of Escherichia coli, which is the most common bacterium in urinary tract infections, in addition to Aspergillus and Klebsiella pneumoniae. Urinary microalbumin (MAU) and urinary microalbumin/urinary creatinine ratio (MAU/UCr) are usually used to diagnose glomerular diseases, such as early renal damage in hypertension, early diabetic nephropathy, renal damage in systemic lupus erythematosus, renal damage in allergic purpura and primary glomerular diseases (glomerulonephritis and nephrotic syndrome, etc.). In contrast, the Department of Nephrology, Hua Shan Hospital, Fudan University, Jing’an Branch, after a 4-year study, found that MAU and MAU/UCr, originally used to diagnose glomerular diseases, could assist in the diagnosis of pyelonephritis. The mean levels of MAU and MAU/UCr were significantly higher before treatment in all cases of urinary tract infection studied, and both were significantly lower after treatment, with medically statistically significant differences compared to the pre-treatment levels. It was also found that when the urine routine was normalized after treatment, but the MAU and MAU/UCr were still elevated in some cases, the bacteria were still present in the urine culture again, and the bacteria were the same as the original culture; when the MAU and MAU/UCr were normalized after treatment, the urine culture was also normalized. This result suggests that elevated MAU and MAU/UCr levels may have some predictive value in determining whether a urinary tract infection is cured. Why do elevated MAU and MAU/UCr occur in pyelonephritis that is not glomerular disease? The author suggests that it may be related to the fact that the infecting bacteria are mostly gram-negative such as Escherichia coli, because this type of bacteria can secrete endotoxin, which can affect the capillary endothelial function on the glomerular filtration membrane, leading to increased permeability of the glomerular filtration membrane, making MAU and MAU/UCr filtration increase and causing elevation. This study gives new clinical significance to the elevated MAU and MAU/UCr levels. The results of this study were published in World Clinical Drugs, Vol. 7, 2010. The authors concluded that after excluding primary and secondary glomerular diseases, as well as systemic diseases affecting the kidneys, elevated levels of urinary microalbumin and urinary microalbumin/urinary creatinine ratio in patients with urinary tract infections may suggest that the patient may have pyelonephritis, i.e., a bacterial infection affecting the kidneys.