Based on PubMed | Is fever a common symptom in systemic lupus erythematosus, and how can I tell if a fever is due to a lupus flare rather than an infection?

Short answer

Yes, fever is fairly common in systemic lupus erythematosus (SLE), often low‑grade and sometimes part of a disease flare. ^[1] Fever can also be caused by infections, which are frequent in SLE and can look similar to a flare, so distinguishing the two usually requires looking at associated symptoms, exam findings, and specific lab markers. ^[2] In general, low‑grade fever with low complement and rising anti‑dsDNA suggests flare, while higher fever with elevated inflammatory markers (like procalcitonin) and neutrophilia points more toward infection. ^{[3] [4]}

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Is fever common in SLE?

• Fever is listed among common SLE symptoms and may occur without another cause during active disease. ^[1]
• People with lupus will sometimes have a low‑grade fever related to the disease, and fever can be an early sign when lupus is flaring. ^{[5] [6]}
• Public health guidance also includes fever as one of the typical lupus symptoms. ^[7]

Bottom line: fever happens in lupus, especially during flares, but it is not specific many fevers are due to infection in people with SLE. ^[2]

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Why it’s hard to tell flare vs. infection

• Infections are common and a leading cause of illness in SLE due to the disease itself and immunosuppressive treatments; infections can mimic an SLE flare with overlapping signs like fever and fatigue. ^[2]
• Indeed, infection and flare can even occur together, so clinicians use a combination of clinical clues and laboratory tests to decide. ^[2]

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Practical clues: flare vs. infection

Clinical features that may suggest flare

• Low‑grade fever with other typical lupus symptoms (joint pain/swelling, rash, chest pain on deep breath, fatigue) when no localizing signs of infection are present. ^[1]
• Known lupus triggers (recent sun exposure, stress) and recurrence of the person’s usual flare pattern. ^[6]
• Swollen lymph glands during a flare can occur, though not specific. ^[5]

Clinical features that may suggest infection

• Higher fever, chills, rigors, new cough or sputum, urinary symptoms, wound redness, or focal pain pointing to a source. ^[2]
• Feeling more acutely ill than during typical flares, especially with respiratory, urinary, or skin signs. ^[2]

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Lab markers and how they help

The following markers are often used together to improve accuracy:

• Complement levels (C3, C4): tend to be decreased during SLE flares, helping point toward immune activity rather than infection. ^[4]
• Anti–double‑stranded DNA (anti‑dsDNA): typically rises with lupus activity and supports a flare when coupled with low complement. ^[2]
• White blood cell differential: neutrophilia and immature granulocytes are more typical of bacterial infection; SLE activity can show normal or lower counts. ^[4]

Inflammatory biomarkers:

• Procalcitonin (PCT): elevated levels (e.g., ≥0.5 μg/L) support bacterial infection rather than lupus flare, as PCT does not correlate with lupus activity and is usually lower in flares than in infections. ^[3]
• C‑reactive protein (CRP): can rise in both, but tends to be higher in bacterial infections; interpretation is improved when combined with PCT and blood counts. ^{[4] [3]}

Special hematology index:

• Delta Neutrophil Index (DNI): reflects circulating immature granulocytes; higher DNI (e.g., ≥2.8%) strongly suggests infection in febrile SLE compared with flare. ^[4]

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Side‑by‑side comparison

Feature	More suggestive of SLE flare	More suggestive of infection
Fever pattern	Often low‑grade; may mirror past flares. [5] [1]	Often higher; may include chills/rigors and focal symptoms. [2]
Associated symptoms	Rash, joint pains, fatigue, pleuritic chest pain; photosensitivity. [1] [6]	Cough/sputum, dysuria, wound redness, focal pain. [2]
Complement (C3, C4)	Decreased. [4]	Often normal. [4]
Anti‑dsDNA	Increased. [2]	No specific change. [2]
WBC/neutrophils	Normal or low; not typically left‑shifted. [2]	Neutrophilia; immature granulocytes elevated. [4]
Delta Neutrophil Index (DNI)	Lower; <2.8% typical in flare. [4]	Higher; ≥2.8% suggests infection. [4]
CRP	Mild to moderate; variable. [4]	Often higher. [4]
Procalcitonin (PCT)	Usually low; not linked to SLE activity. [3]	Elevated (≥0.5 μg/L) supports bacterial infection. [3]
Response to antibiotics	No improvement. [2]	Improvement expected if bacterial infection. [2]

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What to do if you have fever and lupus

• Seek medical evaluation, especially if fever is high, persistent, or accompanied by new localized symptoms (cough, urinary pain, rash with pus) or if you’re on immunosuppressive therapy. Prompt assessment matters because infection can worsen quickly in SLE. ^[2]
• Expect your clinician to review symptoms, examine you, and order targeted labs (CBC with differential, CRP, procalcitonin, complement levels, anti‑dsDNA) and, if needed, imaging or cultures to identify an infection source. ^{[4] [3]}
• Avoid starting or increasing steroids or other immunosuppressants on your own when infection is suspected; treatment decisions usually wait for evaluation because steroids can mask infection signs. ^[2]

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Key takeaways

• Fever is common in SLE and may reflect disease activity (flare), but infection is also common and can look similar. ^{[1] [2]}
• Low complement and rising anti‑dsDNA favor a flare; elevated procalcitonin, higher CRP, neutrophilia, and high DNI favor infection. ^{[4] [3]}
• A careful combination of symptoms, exam, and labs is the safest way to tell the difference. ^[2]