Can Influenza Cause Proteinuria?
Yes, influenza infection can lead to proteinuria, though this is an uncommon complication that occurs through several distinct renal injury mechanisms including acute kidney injury, rhabdomyolysis-induced myoglobinuria, and rarely, direct glomerular disease.
Mechanisms of Proteinuria in Influenza
Rhabdomyolysis-Associated Renal Injury
Myositis with myoglobinuria represents the most common pathway to proteinuria in influenza, typically developing 2-4 days after respiratory symptoms begin to subside, particularly affecting the gastrocnemius and soleus muscles 1.
Rhabdomyolysis occurs in approximately one-third of influenza-associated myositis cases, with elevated creatine phosphokinase levels and myoglobinuria leading to acute kidney injury and proteinuria 2.
The clinical presentation includes severe muscle pain and tenderness to palpation, with complete recovery usually occurring within three days, though renal failure can develop in severe cases 1.
Acute Kidney Injury in Critically Ill Patients
Acute kidney injury develops in critically ill influenza patients through multiple mechanisms: acute tubular necrosis from renal hypoperfusion, myoglobin pigment deposition, and disseminated intravascular coagulation 2.
Underlying conditions associated with influenza-related AKI include older age, diabetes mellitus, obesity, pregnancy, history of asthma, and pre-existing chronic kidney disease 2.
Histologic examination reveals acute tubular necrosis, myoglobin pigment, and DIC changes, with influenza virus detected in kidney tissue of some fatal cases 2.
Direct Glomerular Disease (Rare)
Membranoproliferative glomerulonephritis has been documented following influenza A infection, presenting with hematuria, proteinuria, hypocomplementemia, and hypertension 3.
The glomerular injury pattern shows mesangial hypercellularity, intratubular red blood cell casts, mesangial IgM and C3 deposition, and foot process effacement 3.
Acute tubulointerstitial nephritis with granulomatous changes has been reported with influenza A H1N1, presenting with azotemia, hematuria, and proteinuria 4.
Clinical Recognition
Key Warning Signs
Monitor for proteinuria when patients develop severe muscle pain 2-4 days after initial influenza symptoms, particularly with calf tenderness and difficulty walking 1.
Check for dark urine (myoglobinuria), decreased urine output, or edema suggesting renal dysfunction 2.
Obtain urea and electrolytes in hospitalized patients to detect renal impairment early 1.
Laboratory Evaluation
Creatine phosphokinase should be checked when myositis is suspected, with levels often exceeding 1000 U/L in influenza-associated myositis 1, 5.
Assess urine for myoglobinuria and monitor renal function with BUN, creatinine, and electrolytes until CPK levels normalize 5.
In patients with persistent proteinuria beyond the acute illness, consider urinalysis for red blood cell casts and complement levels to evaluate for glomerulonephritis 3.
Management Approach
Immediate Actions
Aggressive hydration is essential when CPK is extremely elevated (>5-10 times normal) to prevent acute kidney injury from myoglobin precipitation 5.
Monitor renal function daily with BUN, creatinine, and electrolytes until CPK levels trend downward 5.
Avoid NSAIDs if renal function is compromised; prefer acetaminophen for pain management 5.
Prognosis
Most cases of influenza-associated myositis with myoglobinuria are self-limiting, with complete recovery within 3 days when managed with supportive care 1, 5.
Glomerulonephritis associated with influenza can resolve completely within 6 months, as documented in the membranoproliferative case 3.
Severe acute kidney injury requiring dialysis can occur but is uncommon, primarily in critically ill patients with multiple organ dysfunction 2, 6.
Critical Pitfalls
Do not miss rhabdomyolysis by failing to check urine for myoglobin when patients present with severe muscle pain after influenza 5.
Avoid aspirin in children with influenza due to Reye's syndrome risk; this is particularly important when managing myositis-related pain 1, 5.
Do not assume all proteinuria in influenza is benign—persistent proteinuria beyond 10 days warrants nephrology evaluation for possible glomerular disease 3, 4.