cellulitis blood test explained
Informed by recognized medical guidance
Overview
Cellulitis is a common skin infection caused by bacteria entering through a break in the skin. It makes the skin red, swollen, warm, and painful. A blood test can help confirm the infection and guide treatment.
Key facts
- Cellulitis is not contagious – you cannot catch it from someone else.
- Blood tests can show signs of infection, like a high white blood cell count.
- Prompt treatment with antibiotics usually clears the infection within a week or two.
Yes, cellulitis is a common infection that sends many people to their doctor or emergency department each year.
Anyone can get cellulitis, but it is more common in people with breaks in the skin, a weakened immune system, or chronic conditions like diabetes or lymphedema.
Symptoms
- High fever with shaking chills
- Rapidly spreading redness or swelling
- Feeling very unwell, faint, or confused
- Nausea, vomiting, or rapid heart rate – signs of sepsis
- ⚠Fever that does not improve with rest
- ⚠Redness spreading beyond the initial area
- ⚠Severe pain not relieved by over-the-counter pain relief
- ⚠If you have a weakened immune system and notice any signs of infection
Common symptoms
- Redness and swelling of the skin
- Warmth in the affected area
- Pain or tenderness
- Fever and chills
- Tight, glossy appearance of the skin
Symptoms in children
- Redness and swelling, often on the face or legs
- Irritability or fussiness
- Crying when the area is touched
- Fever or lethargy
Symptoms in older adults
- Redness and swelling may be less obvious
- Confusion or sudden change in behaviour
- Loss of appetite or weakness
- Worsening of existing health conditions
Causes
Main causes
- Bacteria (usually streptococcus or staphylococcus) entering through a break in the skin, such as a cut, scrape, insect bite, or surgical wound.
- Pre-existing skin conditions like eczema or athlete's foot that create cracks in the skin.
Risk factors
- Having a weakened immune system (due to diabetes, HIV, chemotherapy, or long-term steroid use)
- Poor blood circulation (peripheral vascular disease)
- Swelling in the arms or legs (lymphedema)
- Obesity
- Recent surgery or skin injury
- Intravenous drug use
When to see a doctor
See a doctor urgently if:
- If you have a fever and the redness is spreading quickly
- If you feel very unwell, faint, or have chills
- If you have a chronic condition like diabetes or heart disease
Book a routine appointment if:
- If you notice a small area of redness, swelling, and warmth that does not improve after a day or two
- If you have a cut or wound that becomes red and tender
Diagnosis
Your doctor will examine your skin and ask about your symptoms. They may order a blood test to check for signs of infection, such as a high white blood cell count, and to identify the bacteria causing the infection.
Tests that may be done
- Complete blood count (CBC) to measure white blood cells and other markers of infection
- Blood culture to look for bacteria in the bloodstream
- Sometimes a wound culture (swabbing the affected area) if there is an open sore
- In rare cases, imaging like ultrasound or MRI to check for deeper infection
What to expect at your appointment
The blood test is a simple needle stick from your arm. Results may take a day or two. Your doctor may start treatment with antibiotics before the results are back, especially if you have fever or spreading redness.
Treatment
Cellulitis is treated with antibiotics. For mild cases, you can take tablets at home. For more serious infections, you may need intravenous (IV) antibiotics in the hospital. Blood tests help your doctor decide which treatment is best and how well you are responding.
Self-care at home
- Rest and elevate the affected limb to reduce swelling
- Apply a cool, damp cloth to the area for comfort
- Keep the skin clean and dry
- Take over-the-counter pain relievers if recommended by your doctor (avoid specific names)
Medical treatments
Antibiotics are the main treatment. Your doctor will prescribe either oral tablets or intravenous (IV) antibiotics based on the severity of the infection. It is important to finish the full course of antibiotics even if you feel better. If you are in hospital, nurses will give the antibiotics through a drip. Always follow your doctor’s advice about treatment.
When is surgery considered?
Rarely, if an abscess (collection of pus) forms, a small procedure to drain the pus may be needed. This helps the infection clear faster.
Living with this condition
Most people recover fully with treatment. Take all your antibiotics as prescribed. Rest and watch for any worsening symptoms. Follow up with your doctor if the redness does not improve after a few days of treatment.
Lifestyle tips
- Keep your skin moisturized to prevent cracks
- Clean cuts, scrapes, and insect bites promptly with soap and water
- Wear protective footwear if you have diabetes or poor circulation
- Avoid scratching insect bites or rashes
Diet and exercise
A balanced diet rich in fruits, vegetables, and protein helps support your immune system. Gentle exercise like walking is fine if you feel well, but rest when you are tired or have fever. Your body needs energy to fight the infection.
Mental health and emotional wellbeing
Having an infection can be stressful and worrying. It is normal to feel anxious about the recovery. Talk to your doctor or a trusted friend about your feelings. If the anxiety becomes overwhelming, consider seeking support from a mental health professional.
Prevention
You can reduce your risk by taking good care of your skin: keep it clean and moisturized, treat cuts promptly, and manage chronic health conditions like diabetes and lymphedema. Also, avoid walking barefoot outdoors.
Complications
If left untreated
- The infection can spread to deeper tissues, forming an abscess
- Bacteria can enter the bloodstream, causing sepsis – a life-threatening condition
- Rarely, the infection can reach the bone (osteomyelitis) or lymph nodes (lymphangitis)
Long-term outlook
With prompt and proper treatment, most people with cellulitis recover completely. Blood tests help ensure the infection is controlled and guide the right antibiotics. Serious complications are rare when treatment is started early.
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
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Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 20, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.