Children’s urine routine test: Does positive urine sugar mean diabetes?

Author: Song Wenqi, National Children's Medical Center (Beijing), Chief Technician, Beijing Children's Hospital, Capital Medical University

Reviewer: Zhang Yu, researcher at Chinese Center for Disease Control and Prevention

When we get a routine urine test report, we usually find marks such as "negative, positive", "+, ++", etc. What do they mean?

Most hospitals use urine multiple module test strips (dry chemical method) for urine chemical testing, that is, soak the test strips in urine, and the chemical components in the urine react chemically with the modules on the test strips, thereby changing the color of the modules. Generally speaking, the greater the color change of the module, the higher the concentration of the corresponding component in the urine. The multiple test strips are placed on the urine dry chemical analyzer for interpretation, and it can be judged whether it is negative, positive, one "+", or four "+". Generally speaking, the more "+", the higher the concentration, so the expression of one "+" and four "+" is a semi-quantitative expression method.

Take urine sugar as an example. Under normal physiological conditions, the human body needs to maintain blood sugar within a certain concentration range. A small amount of glucose can appear in the urine, generally at a concentration of 2-30 mg/dL. Since the renal tubules have the function of reabsorbing glucose, urine sugar is normally negative.

If the glucose test in urine is "±", it means that the glucose concentration in urine is about 50mg/dL. One "+" means that the glucose in urine is qualitatively positive, and the general urine sugar concentration is about 100mg/dL; "++" means that the urine sugar concentration is about 200mg/dL; "+++, +++++" represent strong positive, and the urine sugar concentration is about 500mg/dL and 1000mg/dL respectively. Different instruments and reagents may represent slightly different concentrations, but in general, the more plus signs there are, the higher the glucose content in urine.

Urine sugar is a preliminary indicator for the initial screening of diabetes and the judgment of the severity of the disease. Diagnosis of diabetes also requires blood sugar testing to make an accurate diagnosis.

When conducting qualitative urine sugar testing, you must pay attention to false positives and false negatives.

False positives are often caused by urine contamination by oxidants, such as hydrogen peroxide, chlorine, etc., which can cause false positives for urine sugar. False negatives are caused by urine containing a large amount of salicylic acid, vitamin C, or high specific gravity urine, which can also cause false negatives for urine sugar.

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Diabetes is usually divided into primary diabetes and secondary diabetes, which can occur in children of all ages. Primary diabetes is divided into type 1 diabetes (insulin-dependent diabetes) and type 2 diabetes (non-insulin-dependent diabetes). Secondary diabetes is often secondary to pancreatic diseases and endocrine diseases.

Type 1 diabetes is more common in children, which is caused by insufficient insulin secretion. As living standards improve, the number of children with type 2 diabetes is also increasing.

Children with diabetes may have elevated fasting blood sugar or elevated postprandial blood sugar, which can result in positive urine sugar. Many physiological and pathological factors can affect urine sugar, so positive urine sugar in children does not necessarily mean diabetes.

Diabetes is divided into hyperglycemic diabetes and normal blood sugar diabetes.

Hyperglycemia-induced diabetes:

The first type is ingestive diabetes. For example, if a child consumes a large amount of sugary food or beverages at one time, including excessive glucose intake, it will cause a transient increase in blood sugar and cause diabetes.

The second type is stress diabetes, which is caused by the body's reactive and transient increase in blood sugar due to craniocerebral trauma, such as cerebral hemorrhage, cerebral infarction, etc.

The third type is metabolic diabetes. A typical example is diabetes, which is caused by increased blood sugar due to impaired sugar metabolism, thus causing diabetes.

The fourth type is endocrine diabetes. Endocrine diseases such as hyperthyroidism and acromegaly cause increased blood sugar, thus causing diabetes.

Normoglycemic diabetes:

The patient's blood sugar is normal, but the urine sugar is positive. This is called renal glycosuria, which means that the renal tubular reabsorption capacity of glucose is reduced and the renal glucose threshold is lowered. Therefore, when the blood sugar is normal, there will be glucose in the urine. There are mainly several situations:

The first type is familial renal glucosuria, which is mainly seen in genetic metabolic diseases, such as Fanconi syndrome. The fasting blood glucose and glucose tolerance are normal. Due to the congenital defect of the renal tubules in the ability to reabsorb glucose in the urine, the fasting urine glucose is positive.

The second type is neonatal diabetes, because the renal tubules of newborns are not yet fully capable of reabsorbing glucose, resulting in normal blood sugar and positive urine sugar.

The third type is acquired renal diabetes, which is caused by renal tubular damage due to chronic kidney disease, nephrotic syndrome, etc., which eventually leads to normal blood sugar and positive urine sugar.

We learned earlier that positive urine sugar does not necessarily mean diabetes, and in fact, not all people with diabetes necessarily have positive urine sugar.

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For example, if diabetes is combined with glomerular arteriosclerosis, the renal glucose threshold will increase due to the decrease in renal blood flow and renal filtrate. Although blood sugar is very high, the increased blood sugar cannot be excreted from the urine, so the urine sugar is negative. In addition, in mild diabetes or impaired glucose tolerance, fasting urine sugar may also be negative, but urine sugar may increase after a meal.

If clinicians want to use urine sugar as a qualitative indicator for dietary control of children with diabetes, they can observe it through the positive and negative urine sugar. Because urine is an excretion of the human body, urine sugar testing is a non-invasive test. However, it must be understood that in type 1 diabetes, that is, insulin-dependent diabetes, blood sugar and urine sugar are not necessarily one-to-one. Therefore, in order to diagnose the disease or observe the efficacy, it is also necessary to test blood sugar and glycosylated hemoglobin to make an accurate judgment.