Comparison of FDG-PET/CT and CECT-CAP as Upfront Imaging Modality for the Diagnosis of Pyrexia of Unknown Origin (CET-PET-PUO)

September 8, 2026 updated by: Deba Prasad Dhibar, Post Graduate Institute of Medical Education and Research, Chandigarh

Comparison of FDG-PET/CT and CECT-CAP as Upfront Imaging Modality for the Diagnosis of Pyrexia of Unknown Origin : A Prospective Observational Study

Pyrexia of unknown origin (PUO) remains one of the most challenging diagnostic problems in modern medicine. Despite advances in laboratory diagnostics, microbiological techniques, imaging modalities, and molecular testing, a significant proportion of patients continue to undergo multiple, prolonged, expensive, and often invasive evaluations before a definitive diagnosis is established. PUO is classically defined as fever ≥38.3°C documented on ≥2 occasions AND duration ≥3 weeks or inpatient fever ≥1 week without diagnosis despite routine evaluation.

The etiological spectrum of PUO is broad and heterogeneous. Causes are traditionally grouped into infections, malignancies, non-infectious inflammatory diseases, miscellaneous causes, and undiagnosed cases. Despite systematic evaluation, a definitive diagnosis is not achieved in a substantial proportion of patients, often ranging from 30-50% even in tertiary care centers. This persistent diagnostic uncertainty highlights the need for effective diagnostic strategies that can identify occult disease early and guide targeted investigations.

Imaging plays a pivotal role once baseline routine investigations fail to establish a diagnosis. Conventional contrast-enhanced computed tomography (CECT) of the chest, abdomen, and pelvis is frequently used due to its wide availability and ability to detect structural abnormalities such as abscesses, masses, and lymphadenopathy. However, CECT relies on anatomical changes and may fail to identify early inflammatory or infiltrative disease that lacks overt structural distortion.

In contrast, nuclear medicine modalities enable the identification of pathological processes at the cellular and molecular level. 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) exploits abnormal glucose metabolism in inflammatory, infectious, and malignant tissues. When combined with PET/CT, it enables precise anatomical localization of metabolically active lesions. Numerous studies have shown that FDG PET/CT is valuable in the evaluation of PUO, especially when standard imaging modalities fail to yield a diagnosis.

In a retrospective study, FDG-PET/CT outperformed CECT-CAP for definite diagnosis of PUO with markedly higher localisation (92.2 vs. 51.5 %; p = 0.003). In a comparative multicentre prospective study FDG PET/CT demonstrated significantly superior diagnostic orientation (28.2% vs. 7.8%, p < 0.001) and diagnostic contribution (19.4% vs. 5.8%, p < 0.001) compared with CECT-CAP, and was associated with a markedly shorter time to definitive diagnosis (3.8 vs. 17.6 months, p = 0.02). However in these studies same patient underwent both FDG-PET/CT and CECT-CAP. In a systematic review, meta-analysis FDG PET/CT had pooled diagnostic yield of 56% and diagnostic yield beyond conventional CT at 32%. However another systematic review/meta-analysis similarly reported a higher contributory effect of FDG-PET/CT compared to Total Body CT (75.4% vs 68%,P = .39) for final diagnosis of PUO although it was not statistically significant. However both studies included data from retrospective studies.

Current clinical practice varies with respect to the timing and sequencing of FDG PET/CT and Conventional CECT in PUO evaluation. FDG PET/CT is often used as a second-line investigation after CECT-CAP or when CECT-CAP is inconclusive; however, growing evidence suggests that early use of FDG PET/CT may offer superior diagnostic yield and reduce diagnostic delay. However clear evidence from randomized controlled trials comparing FDG PET/CT and CECT-CAP as upfront investigations is lacking. This uncertainty forms the basis of clinical equipoise and provides the rationale for the present study. In this study we will evaluate and compare the diagnostic localization and diagnostic yield of FDG PET/CT over CECT-CAP for etiological diagnosis of PUO.

Study Overview

Status

Recruiting

Conditions

Intervention / Treatment

Study Type

Interventional

Enrollment (Estimated)

132

Phase

  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact Backup

Study Locations

  • India
    • Chandigarh
      • Chandigarh, Chandigarh, India, 160012
        • Recruiting
        • Post Graduate Institute of Medical Education and Research, Chandigarh, India
        • Principal Investigator:
          • Deba Prasad Dhibar, MD
        • Contact:
        • Contact:

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

No

Description

Inclusion Criteria:

  • Age > 18 years
  • irrespective of gender.
  • Fever ≥38.3°C documented on ≥2 occasions AND duration ≥3 weeks or inpatient fever ≥1 week without diagnosis despite routine evaluation.
  • Routine investigations to be done before labelling PUO: Full history & examination, CBC, ESR/CRP, LFTs, RFTs, blood and urine cultures, urinalysis, ANA, RF, chest X-ray, abdominal ultrasound

Exclusion Criteria:

  • Pregnancy.
  • Known case of immunosuppression
  • Contraindication or allergy to iodinated IV contrast (for CECT-CAP arm) that cannot be corrected
  • Prior FDG PET/CT or CECT-CAP performed prior to randomization for the current febrile illness that would preclude randomization

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Diagnostic
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm
Intervention / Treatment
Experimental: FDG PET/CT
18F-fluorodeoxyglucose positron emission tomography (FDG-PET)
Diagnostic test: FDG-PET
whole body 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) scan
Other: Standard care of therapy
Both the group will receive standard care of therapy and Based on diagnostic localisation patient will be subjected to microbiological, histopathological or molecular based testing when amenable to reach final diagnosis. If assigned investigation didn't provide any diagnostic localization other imaging modality can be used.
Active Comparator: CECT
contrast-enhanced computed tomography (CECT)
Other: Standard care of therapy
Both the group will receive standard care of therapy and Based on diagnostic localisation patient will be subjected to microbiological, histopathological or molecular based testing when amenable to reach final diagnosis. If assigned investigation didn't provide any diagnostic localization other imaging modality can be used.
Diagnostic test: CECT
contrast-enhanced computed tomography (CECT) of chest, abdomen and pelvis

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
• Diagnostic localization
Time Frame: 8 weeks
Diagnostic localization will be defined as number of participants with any abnormal finding of tracer uptake and/or anatomical variations consistent with clinical suspicion that could not be explained by physiological tracer uptake and/or anatomical variations.
8 weeks
Diagnostic yield
Time Frame: 8 weeks
Diagnostic yield will be defined as number of participants with diagnostic localization (organ/tissue) which when subjected to microbiological, histopathological and/or molecular based investigation led to a final diagnosis.
8 weeks

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Time taken for diagnosis
Time Frame: 8 weeks
Number of days taken from enrolment to reach final diagnosis
8 weeks
Need for additional imaging
Time Frame: 8 weeks
Number of participants requiring additional imaging other than primary imaging modality
8 weeks

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Post Graduate Institute of Medical Education and Research, Chandigarh

Investigators

  • Principal Investigator: Deba Prasad Dhibar, MD, Post Graduate Institute of Medical Education and Research, Chandigarh, India

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

April 9, 2026

Primary Completion (Estimated)

June 30, 2027

Study Completion (Estimated)

June 30, 2027

Study Registration Dates

First Submitted

September 8, 2026

First Submitted That Met QC Criteria

September 8, 2026

First Posted (Actual)

September 14, 2026

Study Record Updates

Last Update Posted (Actual)

September 14, 2026

Last Update Submitted That Met QC Criteria

September 8, 2026

Last Verified

September 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

  • INT/IEC/2026/SPL-831

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

NO

IPD Plan Description

All reasonable data requests should be submitted to the principal investigator (DPD) for consideration

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

Subscribe