Utility of serum blood ketone levels and other risk factors for inadequate myocardial glucose suppression ketogenic FDG-PET/CT: a prospective and retrospective cohort study

OBJECTIVES Incomplete myocardial glucose suppression (MGS) in ketogenic 18F-FDG-PET/CT is a common problem that reduces the diagnostic accuracy in detecting myocardial inflammation. This study assesses the usefulness of a dietary logbook, blood ketone testing and risk factors for inadequate MGS. METHODS Retrospective (2022–2024) and prospective (2024–2025) analysis was performed on all patients who underwent a ketogenic 18F-FDG-PET/CT. In April 2024, blood ketone testing, a dietary logbook, and improved dietary guidelines were introduced. All patients were instructed to follow > 24-hour ketogenic diet and > 12-hour fast before imaging. RESULTS After introducing the dietary logbook and guidelines, inadequate MGS rates decreased from 26% to 17% (95 patients 2022–2024 vs 92 patients 2024–2025)(p-value 0.14). Mean blood ketones were significantly lower in patients with incomplete MGS (0.34mmol/L vs 0.76mmol/L, p-value 0.04). On univariate analysis, significant risk factors for inadequate MGS included prednisolone use (75% vs 14.9%, OR: 17.1 [95%CI 1.65-177.04], p = 0.009), low blood ketones (≤ 0.3mmol/L)(OR: 5.77 [95%CI 1.69–19.68], p = 0.003) and female sex (7.5% vs 9.6% in males, OR: 3.57 [95%CI 1.12–11.3], p = 0.025). Multivariate analysis confirmed prednisolone use, low ketones (≤ 0.3mmol/L) and < 24-hour ketogenic diet as independent risk factors. Rates of inadequate MGS were 50%, 26% and 7% for patients with blood ketone levels of 0.1, 0.2–0.3 and ≥ 0.4mmol/L, respectively. All patients on prednisolone with ketones ≤ 0.3mmol/L had inadequate MGS. CONCLUSIONS Dietary logbook and clear instructions improve adherence. Low ketones, prednisolone use and short ketogenic preparation are risk factors for inadequate MGS.