Why Does IgA Nephropathy Cause Blood in Urine During Colds?

If you have IgA nephropathy, getting a cold or sore throat can trigger a flare-up that causes your urine to turn dark—often the color of tea or cola. Seeing this happen can be frightening, but it is a recognized pattern. This color change is caused by visible blood in the urine (gross hematuria). Not everyone experiences visible color changes; for many patients, the flare is microscopic and only detected through testing.

This happens because your immune system’s defense mechanisms in your airway are closely linked to your kidneys ^[1]. According to the leading scientific model, when you get a respiratory infection, your body increases production of the antibody Immunoglobulin A (IgA). In IgA nephropathy, your body makes an abnormal version called galactose-deficient IgA1 ^[2]. These abnormal antibodies combine with other immune proteins to form circulating immune complexes, which then become trapped in your kidney’s filters (the glomeruli) ^[2][3]. This buildup triggers acute inflammation, disrupting the delicate filtration barrier and allowing red blood cells and protein to leak into your urine ^[4][5].

A Clue in the Timing

The rapid appearance of blood in the urine during or within a few days (often 24 to 48 hours) of starting a respiratory illness is called synpharyngitic hematuria ^[6][7]. The prefix “syn-” means “at the same time,” and “pharyngitic” refers to the throat.

This immediate timing is a classic hallmark of IgA nephropathy ^[8]. It often helps doctors distinguish an IgA flare from post-infectious glomerulonephritis (PIGN) ^[9]. In classic PIGN, such as after a strep throat infection, the kidney inflammation and dark urine usually have a delayed onset, appearing 1 to 3 weeks after the infection has resolved ^[10].

However, timing alone cannot definitively diagnose the cause. Certain severe infections, such as a staphylococcus infection, can trigger an infection-related kidney disease that occurs during the active infection and closely mimics an IgA flare ^[11][12].

Why You Need Ongoing Testing

Because synpharyngitic hematuria is a known feature of IgAN, you might assume you don’t need tests if you get a cold. However, new or persistent visible hematuria requires clinical assessment. Flare-ups can temporarily or permanently alter your kidney function, and testing is the only way to measure this. Your care team needs to monitor for:

• Acute Kidney Injury (AKI): Severe gross hematuria can cause obstruction in the kidney tubules or reflect intense inflammation, leading to AKI—a rapid drop in kidney function ^[13]. Recovery is possible but not guaranteed, and AKI requires careful medical management ^[14].
• Worsening Proteinuria: An episode can cause a sudden or lasting increase in the amount of protein leaking into your urine (proteinuria). Persistent proteinuria is a primary risk factor for long-term progression of the disease ^[15][16].
• Ruling Out Other Conditions: Dark urine can also be caused by severe dehydration, other urinary issues, or a different infection. Your doctor may check your blood for a protein called C3 (part of the complement system) ^[9]. While a low C3 level is a clue that points toward infection-related disease rather than an IgAN episode, it is not a diagnosis on its own; doctors interpret C3 alongside your symptoms, kidney function tests, and urinalysis ^[17].

Action Plan: When to Seek Help

Do not dismiss an episode of dark urine as harmless ^[13]. You and your care team should establish a personalized “sick-day plan” detailing exactly what steps to take.

Seek Emergency Care Immediately if you experience:

• An inability to pass urine or a severe, sudden drop in urine output.
• Severe or worsening shortness of breath.
• Chest pain or confusion.
• Very high blood pressure (especially if accompanied by a severe headache or neurological symptoms).

Contact Your Nephrology Team Promptly if you notice:

• New or recurring urine that resembles tea/cola, or contains visible blood.
• New or worsening swelling (edema) in your legs, ankles, or around your eyes ^[18].
• Blood pressure that is higher than the personalized threshold set by your doctor ^[18].

A Warning About Over-the-Counter Medicines

During a cold, it is critical to be careful with over-the-counter (OTC) medications.

• Avoid NSAIDs: Pain relievers like ibuprofen (Advil, Motrin) and naproxen (Aleve) can constrict blood flow to the kidneys and worsen kidney function or raise blood pressure.
• Use Caution with Decongestants: Oral decongestants containing pseudoephedrine or phenylephrine can elevate your blood pressure.
• Do Not Stop Prescribed Medications: Never independently stop taking your prescribed blood pressure or kidney medications during an illness unless directed by your doctor’s sick-day plan. Always check with your pharmacist or nephrologist before starting a new OTC product.