PET-CT in infection and inflammation
PET-CT for Fever — of Unknown Origin
If your doctor has ordered a PET-CT for a fever lasting weeks, that does not necessarily mean cancer is suspected. The scan is one of the most practical ways to locate where an unexplained fever is coming from — and to guide the next investigation.
Medically reviewed by Dr. T. Raghavender Reddy, Medical Oncologist, MBBS · DM (Medical Oncology) · MD (Radiation Oncology) · Last reviewed September 2026
- Not only a cancer test — Prolonged unexplained fever is a recognised indication for PET-CT referral, separate from cancer workups.
- Finds metabolic hotspots — The scan detects areas of high activity — infection, inflammation, or lymphoma — that standard CT may miss.
- TB looks identical here — In this region, tuberculosis on PET appears the same as lymphoma. Tissue is needed to tell them apart.
- Guides the next test — The scan locates where to investigate, not what the final diagnosis is.
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PET-CT is used to find the hidden source of a fever lasting weeks without a clear diagnosis. It detects areas of infection, inflammation, or lymphoma — including tuberculosis, which is common in this region and looks identical to lymphoma on the scan. The scan shows where to look next, not what the final diagnosis is.
At CION, a whole-body PET-CT starts from Rs 10,499 — among the lowest published prices in Hyderabad. Indicative price, as of September 2026.
When does a doctor order PET-CT for fever?
Prolonged unexplained fever — lasting weeks with no cause found after standard blood tests, cultures, and chest imaging — is a recognised indication for PET-CT in both infectious disease and haematology practice.
The scan is not a first-line test. It is ordered when the standard workup has not identified a source and your team needs to know where in the body to investigate further.
The referring doctor is often a physician or infectious disease specialist, not an oncologist. Being referred for this scan does not mean cancer is the working diagnosis.
What does PET-CT find that a standard CT scan misses?
A standard CT shows anatomy — the shape and size of organs and nodes. PET adds metabolic activity, so it can detect a small focus of active infection or inflammation that looks structurally normal on CT alone.
The three main findings in a fever workup are: an active infection such as tuberculosis, a deep abscess, or osteomyelitis; an inflammatory condition such as vasculitis or sarcoidosis; or lymphoma, the malignancy most commonly associated with prolonged fever.
In this region, tuberculosis is especially significant. Active TB in nodes, lungs, or abdomen produces high uptake on PET that looks identical to lymphoma — a biopsy of the active site is needed to tell them apart.
PET-CT Partner Centres
PET-CT Scan Centres in Hyderabad
CION offers PET-CT scans through 4 trusted partner PET-CT centres across Hyderabad, so you can choose the one closest to you. Call 18002028726 and we’ll guide you to the earliest available appointment.
PET-CT Centre — Punjagutta
PET-CT Centre — Himayatnagar
PET-CT Centre — Narayanaguda
These are partner diagnostic centres within the CION network. Toll-free booking: 18002028726.
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What happens after the PET scan?
The radiology report will describe which areas showed abnormal uptake and list the possible causes — a differential, not a confirmed diagnosis.
Your treating team will use that to plan the next step, usually a biopsy of the most accessible active site the scan identified.
If the scan is entirely normal, that narrows the field considerably. Your team will explain what the absence of uptake means for your specific situation and what they intend to do next.
Did you know?
India carries one of the world's largest tuberculosis burdens, and TB is among the leading causes of prolonged unexplained fever in this region.
On PET-CT, active tuberculosis produces the same high-uptake pattern as lymphoma. The image alone cannot distinguish between them — tissue from a biopsy always makes the final call.
Source: WHO Global Tuberculosis Report; ICMR National TB Guidelines
Questions people ask about PET-CT for fever
Can the scan tell whether it is TB or lymphoma?
No, and this is the most important limitation to understand. Both tuberculosis and lymphoma produce high uptake that looks the same on PET. Other infections and inflammatory conditions can too. The scan tells your team which site to target. A biopsy of that site, examined by a pathologist, is what distinguishes TB from lymphoma. Until then, the report correctly lists both as possibilities — and that is the honest position to be in at this stage.
Does this referral mean my doctor suspects cancer?
Not necessarily. PET-CT is a general metabolic imaging tool used across infection, inflammation, and cancer workups alike. Many patients referred for prolonged fever are found to have TB, vasculitis, or another non-cancer cause. The referral is about locating the source of the fever, not a prior assumption about what that source will turn out to be.
Will I need a biopsy after the scan?
In most cases, yes. The scan identifies sites of abnormal activity; a biopsy of the most accessible one provides the tissue needed for a confirmed diagnosis. In some situations, the combined weight of the scan, cultures, blood markers, and clinical history is enough to proceed without a biopsy. Your team will explain which applies to you and, if a biopsy is planned, which site they intend to sample and why.
How is PET-CT different from an ordinary CT scan for this?
CT shows structure: whether nodes are enlarged, whether organs look abnormal in shape. PET adds a layer of metabolic activity — actively infected or inflamed tissue takes up the radiotracer and appears bright on the scan. A site can look structurally normal on CT but be highly active on PET, and that hidden metabolic activity is exactly what causes weeks of unexplained fever without appearing on standard imaging.
What if the PET scan comes back completely normal?
A normal scan is genuinely useful information. It makes a large active infection or lymphoma much less likely and directs your team toward conditions that do not produce high metabolic uptake — certain autoimmune conditions, viral causes, or drug reactions. Your team will explain what it means for your specific case and where the investigation goes next. A normal PET does not mean nothing is wrong.
How long does it take from scan to diagnosis?
The radiology report is typically available within one to two days. If a biopsy follows, pathology results usually take five to ten working days — though TB cultures can take considerably longer. Ask your team for the expected timeline at each step so you are not waiting without a clear date to focus on. If your fever worsens or new symptoms appear in the meantime, contact your team rather than waiting for the scheduled review.
Book a PET-CT at CION from Rs 10,499 — among the lowest published prices in Hyderabad — with an oncologist-reviewed report and a free Rs 950 consultation, across 4 partner centres. Indicative price, as of September 2026.
Explore 94 more Understanding Your PET-CT Report topics
Infection, TB & Inflammation on PET
- Can Tuberculosis Look Like Cancer on a PET Scan?
- Dental Infection and Jaw Uptake on PET
- Fungal Infection and Abscess on PET-CT
- How Long Should You Wait After an Infection Before a PET Scan?
- If It Might Be Infection, What Test Comes Next?
- Inflammation After Injections, Vaccines and Cannulas
- Old Healed TB and Calcified Nodes on PET-CT
- PET-CT for Fever of Unknown Origin
- PET-CT for Suspected Infection in Implants and Prostheses
- PET-CT for Vasculitis and Inflammatory Conditions
- Pneumonia and Recent Chest Infection on PET
- Sarcoidosis on PET-CT: The Great Mimic
- TB or Cancer? How Doctors Tell Them Apart
- Thyroid Uptake on PET: Diffuse vs Focal
False Positives, False Negatives & Pitfalls
- Bladder, Kidney and Ureter Activity on PET
- Bone Marrow Uptake After Growth Factor Injections
- Bowel Uptake: Normal, Inflammation or Something Else?
- Brown Fat Uptake: A Common Cause of Confusing Findings
- Does a Suspicious PET Finding Always Need a Biopsy?
- Getting a Second Read of Your PET-CT Images
- How Often Is a PET-CT Scan Wrong?
- Muscle Uptake After Exercise or Injections
- Thymic and Rebound Uptake in Younger Patients
- Uptake After Radiotherapy: Inflammation or Disease?
- Uptake at a Biopsy or Surgery Site
- What Causes a False Negative on a PET Scan?
- What Causes a False Positive on a PET Scan?
- What Happens If Two Scans Disagree?
- Which Cancers Do Not Show Well on PET-CT?
- Why the Brain Always Lights Up on PET
Incidental Findings
- A Second Unrelated Cancer Found on PET-CT
- An Incidental Bone Finding on PET-CT
- An Incidental Breast Finding on PET-CT
- An Incidental Kidney or Adrenal Finding
- An Incidental Liver Lesion on PET-CT
- An Incidental Lung Nodule Found on PET-CT
- An Incidental Prostate Finding on PET-CT
- An Incidental Thyroid Nodule on Your PET Scan
- Do All Incidental Findings Need Investigation?
- Focal Bowel Uptake: Could It Be a Polyp?
- Incidental Findings on a PET-CT Scan: What They Are
- Incidental Heart Findings on a Cancer PET Scan
- The Cost of Chasing an Incidental Finding
- What to Ask Your Doctor About an Incidental Finding
Reading Your Report: Core Terms
- 'Cannot Be Excluded' and Other Cautious Phrases
- 'Deauville Score' on a Lymphoma PET Report
- 'FDG Avid': What It Means on Your Report
- 'Hypermetabolic': What the Word Actually Means
- 'Hypometabolic' and 'Photopenic' Findings
- 'Impression' vs 'Findings': Which Section Should You Read?
- 'Interval Change' and 'Stable Since Previous Study'
- 'Krenning Score' on a DOTANOC or DOTATATE Report
- 'Lymphadenopathy' on Your PET Report
- 'Metabolically Active Disease': What It Tells You
- 'Metastasis' and 'Distant Spread' on Your Report
- 'Mildly FDG Avid' vs 'Intensely FDG Avid'
- 'No Abnormal FDG Uptake': Is That a Clear Scan?
- 'Physiological Uptake': Normal Areas That Always Light Up
- 'Residual Disease' vs 'Complete Metabolic Response'
- 'Sub-Centimetre Node' and Why Size Matters on PET
- 'Suspicious for Malignancy': How Certain Is That?
- How Long Does a PET-CT Report Take?
- How to Read Your PET-CT Report: A Section-by-Section Guide
- Should You Read Your Own PET-CT Report Before the Consult?
- TNM Staging on a PET-CT Report
- Why Your Report Mentions the Liver and Blood Pool
Response Assessment Scores & Criteria
- Complete Metabolic Response: What It Means
- Deauville Score 1 to 5: The Lymphoma Scale Explained
- End-of-Treatment PET Scan: What It Decides
- How Doctors Judge Whether Treatment Is Working on PET-CT
- Interim PET Scan During Chemotherapy: Why It Is Done
- Metabolic Response vs Size Response: Why They Differ
- PERCIST Criteria: How Metabolic Response Is Measured
- Partial Metabolic Response: Is That Good Enough?
- Progressive Metabolic Disease: What Happens Next
- RECIST vs PERCIST: Size vs Activity
- Stable Metabolic Disease: Good News or Bad?
- Tumour Flare and Pseudoprogression on PET
- What Is a Deauville 3 and Why Is It Ambiguous?
- Why the Scan Says One Thing and You Feel Another
SUV Values Explained
- Comparing SUV Between Two Scans: Is It Meaningful?
- Does a Higher SUV Mean a More Aggressive Cancer?
- Factors That Change Your SUV Reading
- High SUV but Not Cancer: When the Number Misleads
- Is My SUVmax of 4 High? Reading Your Specific Number
- Low SUV but Still Cancer: The PET-Negative Cancers
- SUV in Non-Cancer Conditions
- SUVmax, SUVmean and SUVpeak: What Is the Difference?
- What Is SUV on a PET Scan?
- What Is a Normal SUV Value?
- What SUV Value Indicates Cancer?
- Why Blood Sugar Changes Your SUV Result
- Why Did My SUV Go Down but Not to Zero?
- Why Did My SUV Go Up After Treatment?
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Common questions
Frequently asked questions
Is PET-CT the right scan for prolonged fever, or should I ask for something else?
PET-CT is a well-established investigation for prolonged unexplained fever that remains undiagnosed after standard workup, and it features in infectious disease and haematology guidelines for this purpose. Whether it is the right next step for you depends on what has already been done. Ask your physician why this scan was chosen and what they expect to learn from it — that is a reasonable question to put directly.
Can I have the scan while I am still taking antibiotics?
Active antibiotics can reduce the inflammatory signal from a bacterial infection and may affect what the scan shows. That said, stopping treatment is not always safe, and in many cases the scan proceeds while treatment continues. Tell the imaging team exactly what you are taking. Your doctor will have considered this before referring you, but the team on the day also needs the full medication list.
Is the radiation from the scan safe?
PET-CT uses ionising radiation from both the radiotracer and the CT component. The dose is considered acceptable when there is a clear clinical reason, and prolonged unexplained fever is that kind of reason. If you are pregnant or think you might be, tell your team before the scan is arranged — the risk calculation changes and alternatives may be considered.
Will CION coordinate the scan if I am being seen there?
Yes. PET-CT at CION is arranged through partner imaging centres. If you are being investigated for prolonged fever at a CION centre, your team will coordinate the referral and ensure the images reach the right specialist for review alongside your clinical information.
What should I tell the imaging team before the scan?
Give them your travel history within India, any known TB contact, any prior TB treatment, any autoimmune diagnoses, and a full medication list. In a region where TB is common, this context shapes how the report is written. A radiologist who knows the clinical background interprets the scan more usefully than one who does not — so give as much detail as you can.
How do I manage the wait for results?
Ask your doctor for a specific timeline — when the report is expected, when any planned biopsy will happen, and when you will next speak about results. A concrete date is easier to hold than open-ended waiting. If your fever worsens, new pain develops, or you feel significantly worse before that date, contact your team rather than waiting for the scheduled appointment.