Serum Sodium Changes During Bacterial Infection and Fever
Yes, serum sodium decreases slightly during bacterial infection and fever, with hyponatremia occurring in approximately 28% of patients with community-acquired pneumonia at hospital admission. 1
Magnitude and Frequency of Sodium Decrease
- Hyponatremia (serum sodium <135-136 mEq/L) is present in 27.9% of patients hospitalized with community-acquired pneumonia, with most cases being mild (only 4.1% have sodium <130 mEq/L). 1
- In children with febrile urinary tract infections, serum sodium levels are significantly lower in those with renal cortical defects (135.9 ± 2.4 mEq/L) compared to those without (137.4 ± 2.7 mEq/L), and hyponatremia (≤135 mEq/L) occurs in 74.1% versus 45.3% respectively. 2
- Hyponatremia develops during hospitalization in an additional 10.5% of pneumonia patients, though most cases remain mild (only 2.6% drop below 130 mEq/L). 1
Pathophysiological Mechanism
- The fall in serum sodium is multifactorial, primarily due to increased secretion of antidiuretic hormone (ADH), either appropriately or inappropriately (SIAD). 3
- Interleukin-6 (IL-6) mediates non-osmotic AVP secretion, creating an inverse correlation between IL-6 and plasma sodium levels during infection. 4
- In COVID-19 patients, median IL-6 levels are significantly higher in hyponatremic versus normonatremic patients (43.4 vs 9.2 pg/mL, P<0.001), with a strong negative correlation (R = -0.48, P<0.001). 4
- In bacterial respiratory infections, IL-6 levels are also elevated in hyponatremic patients (122.1 vs 67.1 pg/mL, P<0.05), though the correlation is weaker (R = -0.25, P=0.05). 4
Clinical Significance and Severity Markers
- Hyponatremia at admission correlates with greater initial heart rate (100.2 vs 93.2 beats/min, P=0.03), higher white blood cell count (15,100 vs 12,100/μL, P<0.0001), and higher pneumonia severity index class 4 or 5 (35.7% vs 25.1%, P=0.05). 1
- Serum sodium concentration is negatively correlated with WBC count (r = -0.156, P=0.011) and CRP levels (r = -0.160, P=0.028) in febrile UTI. 2
- Each mEq/L reduction in serum sodium is associated with a 14.4% increased risk of death in COVID-19 patients, and hyponatremia independently predicts in-hospital mortality with a 2.7-fold increase versus normonatremia. 5
- Hyponatremia is associated with increased length of hospital stay and greater mortality risk in community-acquired pneumonia. 1
Common Pitfalls
- Inadvertent administration of hypotonic fluids may worsen hyponatremia and prolong morbidity during infectious illness. 3
- Hyponatremia may not cause specific symptoms and can be overlooked by clinicians, despite reflecting the severity of the underlying infectious process. 3
- Initial treatment with isotonic saline reduces the risk of hospital-acquired hyponatremia, as patients receiving non-isotonic IV fluids are more likely to develop hyponatremia during hospitalization. 1