High Blood Sugar in Cancer: What it Means and When to Worry

High blood sugar (hyperglycemia) can be common during cancer treatment and it’s worth paying attention to, but with monitoring and timely management it can often be kept under control. Certain cancer therapies and supportive medicines especially steroids and some chemotherapy agents can raise blood sugar temporarily or significantly. ^[1] In some regimens, new-onset or worsened hyperglycemia and even ketoacidosis have been reported, underscoring the need for monitoring. ^[2] For people undergoing intensive treatments, the goal is usually to prevent dangerous highs and lows rather than to push blood sugar to perfectly normal levels. ^[3]

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Why blood sugar can rise during cancer care

• Steroids used with chemotherapy: Drugs like dexamethasone are commonly given to prevent nausea but they can raise blood sugar by increasing insulin resistance. ^[1]
• Specific chemotherapy agents: Some drugs (for example, brentuximab vedotin and L‑asparaginase) are linked with new-onset hyperglycemia or severe glucose intolerance, sometimes requiring insulin and treatment adjustments. ^{[2] [4] [5]}
• Stress, infection, and illness: Active cancer, treatment side effects, reduced appetite, vomiting, or dehydration can disrupt usual eating and medication routines, pushing sugars higher or lower. ^[6]
• Underlying risks: Age, weight, prediabetes/diabetes, and reduced activity increase the chance of treatment-related hyperglycemia. ^{[7] [8]}

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Why it matters: potential impacts

• Higher infection risk: Elevated sugars can impair immune function; in vulnerable patients on intensive therapy, overt hyperglycemia has been associated with more invasive infections and higher sepsis-related mortality. [PM14]
• Treatment complications: Serious hyperglycemia including ketoacidosis has been noted with certain agents, requiring prompt evaluation and management. ^{[2] [4] [5]}
• Quality of life and hospital use: When diabetes management is sidelined during cancer care, complications and hospitalizations can increase; coordinated monitoring helps survivorship. ^{[9] [10]}

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How concerned should you be?

It may help to think of concern in tiers:

• Mild, short-term elevations (e.g., fasting under ~180 mg/dL or post‑meal under ~250 mg/dL): During steroid days or certain chemo cycles, this can be expected and often managed with monitoring, hydration, and temporary medication adjustments. ^{[1] [3]}
• Persistent or high readings (≥200 mg/dL repeatedly, or any >300 mg/dL): These levels deserve prompt attention to prevent dehydration, infections, and treatment delays; your team may add or adjust diabetes medicines, including short‑term insulin. ^{[3] [2]}
• Emergency signs: Blood sugar very high with nausea, vomiting, rapid breathing, confusion, or ketones suggests possible ketoacidosis and needs urgent care. ^{[2] [4] [5]}

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Monitoring targets and approach during cancer care

• Individualized goals: Cancer stage, overall health, and treatment plan matter; earlier-stage disease may aim for tighter control (A1c around 6.5–7%), while advanced disease prioritizes safety and avoidance of hypoglycemia. ^[3]
• Frequent checks during high‑risk periods: On steroid days or when starting agents known to raise glucose, monitor more often (for example, before meals and at bedtime), and consider ketone checks if very high. ^{[1] [2] [4]}
• Coordinate across teams: Oncology and primary care/endocrinology coordination helps reduce complications and supports survivorship. ^{[9] [11]}

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Practical steps you can take

• Know your “steroid days”: Ask which days you receive dexamethasone or other steroids; plan extra glucose checks and have a management plan for rises. ^[1]
• Hydration and balanced intake: Treatment side effects can reduce eating; small, frequent meals with protein and fiber and adequate fluids help stabilize sugars. ^[6]
• Medication adjustments: If you use diabetes medications, temporary dose changes or short‑term insulin may be recommended when sugars rise with chemo or steroids. ^{[3] [2] [4]}
• Watch for infection: Report fevers, new cough, painful urination, or wounds that don’t heal promptly, as high sugars can raise infection risk. [PM14]
• Plan follow‑up: Regular review of glucose logs with your care team supports safe treatment pacing and reduces hospitalizations. ^{[9] [10]}

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Special situations

• Therapies with specific warnings:
  • Brentuximab vedotin (ADCETRIS): Reported serious hyperglycemia, including ketoacidosis; monitor closely and seek care for severe symptoms. ^[2]
  • Asparaginase/Erwinase: Can cause marked glucose intolerance; insulin and pausing the drug may be needed. ^{[4] [5]}
• Hospital stays: Inpatient periods are opportunities to optimize glucose control to prevent complications and improve recovery. [PM20]

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Bottom line

High blood sugar during cancer care is common and manageable, but it deserves attention. The main goals are to avoid dangerous highs and lows, reduce infection risk, and keep treatment on track. ^[3] Proactive monitoring, timely medication adjustments, and clear communication with your care team usually keep you safe. ^{[9] [1] [2]}