Causes of Temporary Proteinuria
Proteinuria, clinically referred to as the presence of excess protein in urine, can manifest as a temporary condition or may develop into a chronic issue due to kidney diseases. The transient types of proteinuria can be attributed to several factors, including:
- Emotional stress.
- Fever.
- Exposure to extremely cold temperatures.
- Dehydration.
- Intense physical exercise.
Causes of Persistent Proteinuria
The presence and type of protein in urine can indicate either a renal impairment affecting the kidney’s ability to reabsorb proteins or an overproduction of proteins by the body. The causes of persistent proteinuria can be categorized as follows:
Glomerular Diseases
Glomerular diseases represent one of the most common reasons for significant proteinuria, defined as the loss of more than 2 grams of protein in urine per day. Normally, the glomeruli, which are networks of capillaries, allow small molecules and liquids to pass through while preventing larger molecules like proteins from leaking into the urine. However, when these structures are diseased, their filtration ability is compromised. The conditions leading to glomerular diseases include:
- Primary glomerular diseases, such as:
- IgA nephropathy.
- Glomerulonephritis.
- Secondary diseases, including:
- Preeclampsia.
- Diabetes mellitus.
- Infections.
- Chronic rejection of transplanted kidneys.
- Amyloidosis.
- Cancers, including lymphomas.
- Lupus nephritis.
- Certain medications, like lithium, non-steroidal anti-inflammatory drugs, penicillamine, and heroin.
Tubular Kidney Diseases
Tubular kidney diseases diminish the ability of the proximal convoluted tubule to reabsorb proteins, particularly small molecular-weight proteins that are typically fully reabsorbed under normal circumstances. The protein levels leaking into urine in such conditions are generally less than 2 grams daily, which may not always be detectable by standard urine tests, potentially yielding false negative results. Common causes include:
- Acute interstitial nephritis.
- Use of analgesics.
- Immunosuppressive medications.
- Sjögren’s syndrome.
- Cryoglobulinemia.
Elevated Protein Levels in the Body
An excessive production of small molecular-weight proteins by the body can result in their infiltration into the urine, thereby putting stress on the proximal convoluted tubules responsible for their reabsorption. This can lead to increased levels of protein in urine due to conditions such as:
- Hemoglobinuria.
- Myoglobinuria.
- Multiple myeloma.
- Amyloidosis.
- Monoclonal gammopathy.
Additional Causes
Other factors that may contribute to proteinuria include:
- Endocarditis.
- Hypertension.
- Heart diseases.
- Malaria.
- Orthostatic proteinuria.
- Sarcoidosis.
- Rheumatoid arthritis.
- Pregnancy.
- Sickle cell anemia.
Risk Factors
Certain factors can increase the likelihood of developing proteinuria. These include:
- Aged over 65 years.
- Obesity.
- Family history of kidney diseases.