Is Proteinuria with a Positive/Negative Result a Sign of Nephritis?
Discovering a (±) result for protein in your urine test can be concerning, but it's important to understand that this finding alone does not necessarily indicate nephritis. While kidney inflammation—commonly referred to as nephritis—can indeed present with symptoms like hematuria (blood in urine) and proteinuria (protein in urine), a trace or borderline positive protein result has multiple potential causes, many of which are benign or temporary.
What Does Urine Protein (±) Mean?
A urine protein reading marked as (±) typically indicates a very low level of protein—just above the detection threshold. This slight elevation doesn't automatically point to chronic kidney disease or glomerular damage. Instead, it may reflect transient physiological changes, minor bodily stress, or even testing variability. Further evaluation is essential before jumping to conclusions.
Common Causes of Mild Proteinuria
1. Physiological (Transient) Proteinuria
This is one of the most frequent explanations for a fleeting protein (±) result. Healthy individuals may temporarily show protein in their urine due to factors such as:
- Fever or recent infection
- Intense physical exercise
- Emotional stress
- Exposure to extreme temperatures
These conditions can increase glomerular permeability briefly, allowing small amounts of protein to leak into the urine. Once the trigger resolves, protein levels typically return to normal without treatment. Repeating the urinalysis after rest and hydration often confirms this benign pattern.
2. Orthostatic (Postural) Proteinuria
Commonly seen in adolescents and young adults, orthostatic proteinuria occurs when protein appears in the urine while standing but disappears when lying down. It's usually harmless and often discovered during routine school or sports physicals.
How it's diagnosed: Doctors perform a "postural test"—collecting urine samples after both overnight recumbency (first-morning void) and after several hours of upright activity. If protein is only present during the day, orthostatic proteinuria is likely. Most cases resolve naturally with age and do not progress to kidney disease.
3. Urinary Tract Infections (UTIs)
Infections anywhere along the urinary tract—including the bladder (cystitis) or kidneys (pyelonephritis)—can lead to inflammation and increased permeability of the urinary epithelium. This may allow proteins to appear in the urine, even if kidney function remains intact.
Other signs of UTI include:
- Burning during urination
- Frequent urge to urinate
- Cloudy or foul-smelling urine
- Lower abdominal discomfort
Treating the infection typically resolves the proteinuria.
4. Systemic Conditions Affecting Protein Levels
Sometimes, protein-like substances detected in urine aren't actually albumin but other proteins released due to systemic issues. These include:
- Myoglobinuria: Caused by rhabdomyolysis (muscle breakdown), often after severe trauma, intense exercise, or certain medications.
- Hemoglobinuria: Occurs when red blood cells break down in circulation (intravascular hemolysis), releasing hemoglobin into the urine.
In these cases, standard dipstick tests may register a positive protein result, but further testing (like urine protein electrophoresis or plasma free hemoglobin) is needed to clarify the diagnosis.
When Should You Be Concerned About Kidney Disease?
While isolated (±) proteinuria is rarely a red flag, persistent protein in repeated tests—especially when combined with other abnormalities—warrants further investigation. Signs that may suggest underlying nephritis or chronic kidney disease include:
- Consistently elevated protein on multiple urine tests
- Visible blood in urine (gross hematuria)
- High blood pressure
- Swelling in the face, hands, or legs (edema)
- Abnormal kidney function tests (elevated creatinine or reduced eGFR)
If any of these are present, your healthcare provider may recommend additional diagnostics such as a 24-hour urine collection, urine microalbumin-to-creatinine ratio, blood work, or even imaging studies.
Bottom Line: Don't Panic—Get Clarity
A single urine test showing protein (±) should not be interpreted in isolation. Nephritis cannot be diagnosed based solely on a borderline positive dipstick result. Many non-threatening, reversible conditions can produce similar findings. The key is follow-up: repeat testing under proper conditions, clinical correlation, and professional medical assessment are crucial for accurate diagnosis.
If you're concerned about your kidney health, consult your doctor for personalized guidance. Early and appropriate evaluation ensures peace of mind—and timely intervention if truly needed.