Hematuria is the medical term for blood found in the urine, and its appearance during an infection can be alarming. The SARS-CoV-2 virus, which causes COVID-19, is known primarily for respiratory illness, but it also affects many other organ systems, including the kidneys and urinary tract. Renal abnormalities, such as the presence of blood and protein in the urine, are frequently recognized complications of moderate to severe COVID-19 infection. These kidney-related issues are common among hospitalized patients and indicate a more widespread systemic effect of the virus on the body.
Identifying Hematuria Associated with COVID-19
Hematuria is categorized into two main types based on detection. Gross hematuria is visible to the naked eye, causing the urine to appear pink, red, or cola-colored. Microscopic hematuria, which is far more common in the context of COVID-19, can only be seen when a urine sample is examined under a microscope in a laboratory setting.
This microscopic presence of blood is often discovered incidentally during routine urinalysis performed when a patient is hospitalized. Studies focusing on patients with COVID-19 pneumonia have reported a significant incidence of hematuria, with rates sometimes exceeding 40% of the cohort. In severe cases, the prevalence has been noted to be even higher, nearing 80% in certain patient groups.
The presence of blood in the urine, particularly when accompanied by protein (proteinuria), signals kidney involvement and potential damage. This renal manifestation is frequently linked to the development of Acute Kidney Injury (AKI) during the course of the disease. Hematuria’s frequency highlights the kidneys’ susceptibility to the destructive processes triggered by the SARS-CoV-2 infection.
Mechanisms of Kidney and Urinary Injury from SARS-CoV-2
The injury leading to blood in the urine is caused by a combination of three distinct biological pathways, rather than a single factor.
Direct Viral Action
One significant mechanism involves the direct action of the SARS-CoV-2 virus on kidney cells. The virus uses the Angiotensin-Converting Enzyme 2 (ACE2) receptor to enter host cells, and this receptor is highly expressed on kidney cells, particularly on proximal tubular cells and podocytes. Direct binding and entry allow the virus to replicate within these renal cells, causing cellular damage and death, known as acute tubular injury. This direct cytopathic effect disrupts the delicate filtering and reabsorbing structures of the kidney, allowing red blood cells to leak into the urine. Evidence includes the visualization of virus-like particles within kidney tissue samples from deceased patients.
Systemic Inflammation
A second major contributor is the systemic inflammatory response, often called a “cytokine storm” in severe cases. The body’s overwhelming immune reaction releases inflammatory molecules that damage the endothelial lining of blood vessels, including the delicate capillaries of the kidney’s filtering units (glomeruli). This damage can result in glomerulonephritis, where inflamed filtering membranes become leaky, leading to the passage of blood into the urinary space.
Hypercoagulability
Finally, COVID-19 often induces a state of hypercoagulability, meaning the blood has an increased tendency to clot. This results in the formation of microscopic blood clots, or microthrombi, within the small blood vessels of the kidneys. These tiny blockages obstruct blood flow, causing localized tissue damage and ischemia in the nephrons, further damaging renal structures and contributing to hematuria.
Clinical Management and Prognosis
Any person who notices a sudden change in urine color, especially to pink, red, or brown, should seek medical attention immediately. While microscopic hematuria is often an incidental finding in a hospital setting, visible (gross) hematuria warrants prompt evaluation to rule out other serious non-COVID-related causes, such as kidney stones, urinary tract infections, or malignancy. Diagnosis begins with a thorough urinalysis to confirm the presence of blood and protein. This is followed by blood tests specifically measuring blood urea nitrogen (BUN) and creatinine to check kidney function.
Management of hematuria associated with COVID-19 focuses primarily on treating the underlying viral infection and its severity. Supportive care is provided to maintain overall kidney function and fluid balance while the body fights the virus. This support may involve careful monitoring of hydration and sometimes the use of dialysis if kidney function declines to severe Acute Kidney Injury (AKI).
The prognosis for COVID-19-associated kidney complications is varied and depends on the overall severity of the infection. Many patients who develop hematuria and AKI experience a resolution of symptoms and recovery of kidney function within a few weeks. However, renal complications, including AKI, are associated with a higher rate of mortality in hospitalized patients. While the majority of kidney injury is acute and reversible, a small percentage of patients may experience long-term damage that progresses toward Chronic Kidney Disease (CKD).