Is Blood in Urine Always a Sign of Nephritis?

Blood in the urine, medically known as hematuria, is not necessarily an indication of nephritis. Hematuria refers to the presence of red blood cells in a urinalysis, sometimes visible only under a microscope (microscopic hematuria) or noticeable by a change in urine color (gross hematuria). While kidney inflammation—commonly referred to as nephritis—is one potential cause, numerous other underlying conditions, both medical and surgical, can lead to this symptom.

Common Causes of Hematuria

Hematuria can stem from a wide range of health issues, and it's essential to differentiate between them for accurate diagnosis and treatment. Broadly speaking, causes fall into two main categories: urological (surgical) and nephrological (medical).

Surgical Causes: Structural or Anatomical Issues

Conditions affecting the urinary tract outside the kidney's filtering units often result in non-glomerular hematuria. These include:

Urinary stones (nephrolithiasis): Hard mineral deposits in the kidneys or ureters that can irritate the lining and cause bleeding.
Urinary tract infections (UTIs): Bacterial infections in the bladder or urethra may lead to inflammation and blood in the urine.
Bladder or kidney tumors: Both benign and malignant growths can present with painless hematuria, especially in older adults.
Congenital abnormalities: Some individuals are born with structural irregularities in the urinary system that predispose them to bleeding.

In these cases, the red blood cells typically maintain their normal shape because they are not filtered through damaged glomeruli. This distinction is critical in identifying the root cause.

Medical Causes: Glomerular Diseases Like Nephritis

Glomerular hematuria originates from damage within the kidney's filtration system. The most common medical cause is various forms of glomerulonephritis, particularly:

IgA nephropathy (Berger's disease): An immune-mediated condition where IgA antibodies deposit in the glomeruli, causing inflammation and recurrent episodes of hematuria, often following upper respiratory infections.
Other types of glomerulonephritis: Including membranous nephropathy, lupus nephritis, and post-infectious glomerulonephritis.

These conditions often come with additional symptoms such as proteinuria (excess protein in urine), high blood pressure, and swelling (edema), especially around the eyes and legs.

How Doctors Diagnose the Source of Hematuria

To determine whether hematuria is due to a kidney disease like nephritis or a structural issue, clinicians use specialized diagnostic techniques. One of the most effective methods involves examining the urine sediment under a phase-contrast microscope.

Dysmorphic red blood cells—those with irregular shapes, blebs, or fragmented membranes—are strong indicators of glomerular origin. These deformities occur as red blood cells squeeze through a damaged glomerular basement membrane, a hallmark of nephritis.

In contrast, if the red blood cells appear uniform and retain their typical biconcave shape, the source is likely non-glomerular, pointing toward urological causes such as infection, stones, or tumors. In such cases, further imaging—like ultrasound or CT scans—and cystoscopy may be recommended.

When to Seek Medical Attention

While occasional, mild hematuria might not always signal a serious problem, persistent or unexplained blood in the urine should never be ignored. Early evaluation helps rule out severe conditions like cancer or progressive kidney disease.

Key warning signs that warrant prompt medical investigation include:

Painful urination or flank pain
Visible blood in the urine
Swelling, fatigue, or foamy urine (indicative of protein loss)
A personal or family history of kidney disease

Ultimately, discovering hematuria during a routine check-up doesn't mean you have nephritis—but it does mean further assessment is needed. With proper testing and expert interpretation, most causes can be accurately identified and effectively managed.