What Is Proteinuria?

Proteins are large biomolecules that are essential for a lot of functions in the body, including growth and repair of cells. These proteins need to remain in the blood to reach the required parts of the body and carry out its function. On the other hand, the kidneys are involved in filtering the blood to remove waste and excess water through urine. When the kidneys start malfunctioning, they may allow proteins to pass through to the urine. Increased levels of protein in the urine is called proteinuria.

While small levels of protein in the urine do not lead to symptoms, higher levels of protein can cause foamy or bubbly urine, swelling of hands and feet, increased frequency of urine, vomiting and muscle cramps.

Protein in the blood is detected by a urine test. The ratio between levels of albumin (a small protein) and creatinine (a waste product) is measured and if above a certain threshold, it indicates presence of proteinuria.

What Causes Proteinuria?

In many cases, a person might have short-term proteinuria due to issues like dehydration, stress, cold temperatures, fever, high intensity of physical activity or kidney stones. In these mild and temporary cases, treatment might not be required, or specific treatment related to the cause will be administered.

If proteinuria is present over a long period of time, it could be an early indication of chronic kidney disease. The two major causes of chronic kidney diseases are high blood pressure and diabetes. Here, we will further discuss diabetes and glucose tolerance related to proteinuria.

As a side note, apart from chronic kidney disease, proteinuria may also occur in other serious health conditions including immune disorders, cancer, cardiovascular diseases and preeclampsia in pregnant woman.

Diabetes and Kidney Diseases

Type 2 diabetes is a condition where insulin, a hormone that regulates the sugar in the blood, does not function effectively. If not regulated, increased levels of sugar or glucose in the blood can damage various organs in the body including the kidneys.

The damage can occur in multiple ways. The increased sugar in the blood can cause blood vessels in the kidneys to constrict (endothelial dysfunction) which can damage the filtering function of the kidney. With diabetes, there can be damage to the nerve function as well which can disrupt the communication between brain and bladder. If the bladder does not get the message to pass urine in time, it can put pressure on the kidneys and damage its function.

Independent of diabetes causing kidney damage, type 2 diabetes and proteinuria have similar clinical features. In both cases, there is increase in inflammation and dysfunction of blood vessels (endothelial dysfunction) in the body.

Prediabetes and Proteinuria Levels

Since it is well known that diabetes can cause kidney damage, most diabetic patients are regularly checked for this health condition. However, before becoming diabetic, patients may be identified at a stage where glucose levels are higher than normal but are not considered diabetic. They are known to be prediabetic.

To find out if someone is prediabetic, a blood test can be done to measure the levels of glucose attached to the hemoglobin (called HbA1C). This gives the average glucose levels present over 2 to 3 months. When the level of HbA1C is less than 5.6, it is considered normal. From 5.7 to 6.4, it is considered prediabetic, and when higher than 6.5, it is considered diabetic.

Because about 33% of newly detected diabetic patients have some extent of kidney-related issues, the question arises whether prediabetic patients might already have an increased risk of proteinuria and kidney disease. While the research in this area has not yielded definitive results, a recent open access article addressed this question by analyzing the health history from 1.8 million patients. These patients were specifically selected for not having taken any glucose-lowering medication at the start of when their data was studied.

Some trends that were observed were that the proportion of men increased when the glucose category level increased. Also, the number of people who were overweight, smoked cigarettes or had hypertension increased with higher levels of glucose. The main observation was that the proteinuria levels in the blood increased with increasing glucose levels. Additionally, when the yearly glucose levels (HbA1C) increased by 0.5% or more, there was a greater risk for proteinuria, especially in those patients having prediabetes. This risk was observed even if people with hypertension were excluded or in subgroups divided based on age and sex. More interestingly, the authors found that if the glucose levels could be brought back to normal, the increase in proteinuria could be prevented.

Take-Home Message

Apart from diabetic patients, patients having prediabetes are already at a risk of having increased proteinuria, potentially leading to chronic kidney disease. However, detecting this early by routine tests and consultations with the doctor can help prevent the kidney from further damage.