Bedside Snapshot
- Normal (Adult)
- Fasting 70–99 mg/dL (3.9–5.5 mmol/L)
Treat hypoglycemia below 70 mg/dL (3.9 mmol/L) - Critical Values
- <50 or >450 mg/dL (<2.8 or >25.0 mmol/L)
Typical; lab-specific
Level 2 hypoglycemia: <54 mg/dL (<3.0 mmol/L) - High Suggests
- DKA or HHS
- New or uncontrolled diabetes
- Stress: sepsis, MI, stroke, trauma
- Steroids, dextrose infusion
- Low Suggests
- Insulin or sulfonylurea excess
- Alcohol, starvation, liver failure
- Sepsis, adrenal insufficiency
- Delayed sample (spurious)
- Act Now If
- <70 mg/dL and symptomatic or altered: oral glucose if safe to swallow, else IV/IO D10 or glucagon; recheck at 15 min.
High with vomiting, Kussmaul breathing or confusion: suspect DKA/HHS. - Watch Out For
- Capillary meter results in shock, dehydration, anemia or hypoxia can be falsely high or low; confirm a value that does not fit the patient with a venous or lab sample
Reference & Critical Ranges
Lab-specific ranges: Every lab sets its own intervals, and analyzer and population change them too. Trust the range printed on your lab report. The values below are typical.
Reference ranges
| Population | Conventional | SI | Notes |
|---|---|---|---|
| Adult, fasting | 70–99 mg/dL | 3.9–5.5 mmol/L | Fasting means no caloric intake for at least 8 hr; 100–125 mg/dL is prediabetes, ≥126 mg/dL is the diabetes range |
| Adult, 2 hr after 75 g oral glucose (OGTT) | <140 mg/dL | <7.8 mmol/L | Laboratory venous plasma only; 140–199 mg/dL is impaired glucose tolerance |
| Hospitalized adult on insulin (ICU and most ward patients) | Target 140–180 mg/dL | 7.8–10.0 mmol/L | Start or intensify insulin for persistent glucose ≥180 mg/dL (10.0 mmol/L), confirmed twice in 24 hr |
| Pregnancy, 24–28 weeks (one-step 75 g OGTT) | Fasting <92, 1 hr <180, 2 hr <153 mg/dL | <5.1, <10.0, <8.5 mmol/L | Any one value at or above these thresholds diagnoses gestational diabetes; the two-step method uses other cut-offs |
| Older adult | Same as adult | Same as adult | Same interval; hypoglycemia risk rises with insulin, sulfonylureas and kidney disease |
| Neonate, first 72 hr (at-risk infant) | Keep ≥47 mg/dL | ≥2.6 mmol/L | Healthy term newborns can dip to 32 mg/dL (1.8 mmol/L) at 1 hr of age; at-risk infants below 47 mg/dL need intervention. Other societies (for example, the Pediatric Endocrine Society and AAP) use different thresholds; follow the local neonatal protocol |
| Neonate after 72 hr | Keep ≥60 mg/dL | ≥3.3 mmol/L | Lower values are persistent hypoglycemia; investigate if ≤50 mg/dL (2.8 mmol/L) persists |
| Infant (after the first days), child, adolescent | 70–99 mg/dL fasting | 3.9–5.5 mmol/L | Same as adult; children under 4 yr may fall below 70 mg/dL with ketosis after an overnight fast |
Severity & critical values
| Level | Conventional | SI | What it means / typical findings |
|---|---|---|---|
| Level 1 hypoglycemia | 54–69 mg/dL | 3.0–3.8 mmol/L | Alert value: treat. Tremor, sweating, palpitations, hunger |
| Level 2 hypoglycemia | <54 mg/dL | <3.0 mmol/L | Clinically significant: neuroglycopenic symptoms (confusion, behavior change); needs immediate correction |
| Level 3 hypoglycemia | No set number | — | Severe event: altered mental or physical function needing another person to recover (seizure, coma) |
| Critical (low) | <50 mg/dL | <2.8 mmol/L | Typical laboratory call value; lab-specific (some labs call <40 mg/dL) |
| Inpatient hyperglycemia | ≥180 mg/dL | ≥10.0 mmol/L | Persistent values: start or intensify insulin |
| DKA glucose criterion | ≥200 mg/dL, or known diabetes at any glucose | ≥11.1 mmol/L | DKA also needs β-hydroxybutyrate ≥3.0 mmol/L and acidosis |
| Critical (high) | >450 mg/dL | >25.0 mmol/L | Typical laboratory call value; lab-specific. Check ketones, venous gas, electrolytes and osmolality |
| HHS glucose criterion | ≥600 mg/dL | ≥33.3 mmol/L | With effective osmolality >300 mOsm/kg, no significant ketosis or acidosis; altered mentation common |
Critical values: <50 mg/dL or >450 mg/dL (<2.8 or >25.0 mmol/L) are typical call values, and each lab sets its own. Don't wait for the critical call. Treat any glucose <70 mg/dL that comes with symptoms. In a sick patient on an SGLT2 inhibitor, look for DKA at any glucose.
Conversion: mg/dL × 0.0555 = mmol/L (mmol/L × 18 = mg/dL)
Corrected sodium in hyperglycemia
Corrected Na⁺ = measured Na⁺ + 1.6 × (glucose − 100) ÷ 100
For every 100 mg/dL of glucose above 100, measured Na⁺ drops about 1.6 mEq/L. Read the corrected value. In hyperglycemia, a normal or high result means a large free-water deficit.
Effective serum osmolality
2 × Na⁺ (mEq/L) + glucose (mg/dL) ÷ 18
Normal sits about 275–295 mOsm/kg. >300 mOsm/kg meets the HHS criterion. Total measured osmolality >320 mOsm/kg is the alternative.
Causes of Abnormal Results
High (hyperglycemia: fasting ≥126 mg/dL; inpatient ≥180 mg/dL)
| Mechanism | Common causes | Bedside clue |
|---|---|---|
| Absolute insulin deficiency | Diabetic ketoacidosis (DKA): type 1 diabetes, new-onset diabetes, missed insulin, insulin pump failure, infection | Vomiting, abdominal pain, Kussmaul breathing, fruity breath; ketones high |
| Relative insulin deficiency with dehydration | Hyperosmolar hyperglycemic state (HHS): usually type 2 diabetes, older adults, infection, poor fluid intake | Glucose often ≥600 mg/dL, profound dehydration, confusion or coma, little ketosis |
| Stress (counter-regulatory hormones) | Sepsis, myocardial infarction, stroke, trauma, burns, surgery | High glucose without known diabetes; marks a sicker patient |
| Drug-induced | Glucocorticoids, thiazides, atypical antipsychotics (olanzapine, clozapine), tacrolimus, HIV protease inhibitors, catecholamine infusions | Morning prednisone: normal fasting value, afternoon-to-evening peak |
| Iatrogenic or spurious | Dextrose-containing IV fluids, parenteral or enteral nutrition, sample drawn above a running dextrose infusion | Value out of keeping with the patient; redraw from the other arm |
| Undiagnosed or uncontrolled diabetes | Type 2 or type 1 diabetes; gestational diabetes | Polyuria, polydipsia, weight loss; A1C ≥6.5% |
| Pancreatic or endocrine disease | Pancreatitis, pancreatic cancer, cystic fibrosis, hemochromatosis; Cushing syndrome, acromegaly, pheochromocytoma, hyperthyroidism, glucagonoma | Abdominal pain, steroid or catecholamine features |
Euglycemic DKA: A real share of DKA cases arrive with glucose <200 mg/dL (11.1 mmol/L). Reported proportions swing widely with definition and population. The causes include sodium-glucose cotransporter 2 (SGLT2) inhibitors (empagliflozin, dapagliflozin, canagliflozin), pregnancy, low food intake, insulin taken before arrival, alcohol and liver failure. A normal glucose never rules out DKA in a vomiting, tachypneic patient. Check ketones and a venous gas.
Low (hypoglycemia: <70 mg/dL; Level 2 <54 mg/dL)
| Mechanism | Common causes | Bedside clue |
|---|---|---|
| Excess insulin effect | Insulin: dose error, missed meal, exercise, pump malfunction, overdose; insulin given for hyperkalemia | Known diabetes; long-acting insulin and hyperkalemia doses can cause lows hours later |
| Insulin secretagogues | Sulfonylureas (glyburide, glipizide, glimepiride); meglitinides | Recurrent lows: half-lives of 12–60 hr; a small dose can cause hypoglycemia in a child |
| Impaired glucose production | Alcohol, starvation or malnutrition, liver failure | Intoxicated or malnourished; ketosis with low glucose; glucagon may not work |
| Critical illness | Sepsis, kidney failure (slower insulin clearance), adrenal insufficiency | Shock; low Na⁺ and high K⁺ suggest adrenal crisis |
| Other drugs | Fluoroquinolones, quinine, pentamidine; beta-blockers blunt warning symptoms | Recent new medication; hypoglycemia without diabetes |
| Endogenous or factitious insulin | Insulinoma, hypoglycemia after gastric bypass, insulin autoimmune hypoglycemia; covert insulin or sulfonylurea use | Whipple triad without a clear cause; draw insulin, C-peptide and a sulfonylurea screen during the low |
| Neonatal and pediatric | Infant of a diabetic mother, preterm, small or large for gestational age, perinatal asphyxia; congenital hyperinsulinism; inborn errors (glycogen storage, fatty-acid oxidation disorders) | Jitteriness, poor feeding, apnea, seizure; low values persisting beyond 72 hr |
| Spurious (pseudohypoglycemia) | Delayed sample processing, marked leukocytosis, poorly perfused finger on a meter | Low result in a well, asymptomatic patient; see Interfering Factors |
Sulfonylurea or long-acting insulin overdose: One dextrose dose does not end this event. The low can come back for many hours. Transport and observe, even after a full recovery. Never release a patient taking a sulfonylurea from the scene.
Interpretation & Bedside Approach
Step-by-step approach
- Is it real? Match the number to the patient. Repeat an unexpected meter result, then confirm with a laboratory sample if the repeat agrees; suspect a sample drawn above a dextrose infusion, a delayed sample or a poorly perfused finger.
- How sick is the patient? Check airway, mental status, perfusion and breathing pattern. Every patient with altered mental status, seizure, stroke symptoms or syncope gets a glucose check.
- Low: treat first, investigate second. Classify by ADA level (Level 1 54–69, Level 2 <54 mg/dL, Level 3 severe event), correct it, then find the cause: which insulin, a sulfonylurea, alcohol, sepsis, missed meals.
- High: look for a crisis. Check β-hydroxybutyrate (BHB), venous pH, bicarbonate, anion gap, K⁺, corrected Na⁺ and effective osmolality; ask about SGLT2 inhibitors and insulin pump use.
- Classify with current criteria. Use the 2024 ADA/EASD/JBDS/AACE/DTS hyperglycemic-crises criteria for DKA and HHS, the ADA levels for hypoglycemia and the ADA 2026 criteria for outpatient diagnosis of diabetes.
- Trend and escalate. Trend beats a single value: on an insulin infusion, check glucose every 1–2 hr. Severe DKA, HHS, altered mental status or a critical illness as the trigger means ICU-level care.
DKA vs HHS (2024 hyperglycemic-crises consensus)
| Criterion | DKA (all three) | HHS (all four) |
|---|---|---|
| Glucose | ≥200 mg/dL (11.1 mmol/L) or known diabetes | ≥600 mg/dL (33.3 mmol/L) |
| Ketones | BHB ≥3.0 mmol/L or urine ketones ≥2+ | No significant ketosis: BHB <3.0 mmol/L or urine ketones <2+ |
| Acid–base | pH <7.30 and/or HCO₃⁻ <18 mmol/L | pH ≥7.30 and HCO₃⁻ ≥15 mmol/L |
| Osmolality | Not a criterion | Effective >300 mOsm/kg or total >320 mOsm/kg |
| Resolution | Ketones <0.6 mmol/L and pH ≥7.3 or HCO₃⁻ ≥18 mmol/L | Osmolality <300 mOsm/kg, glucose <250 mg/dL, urine output >0.5 mL/kg/hr, cognition improved |
Mixed DKA/HHS shows overlapping features in more than one-third of hyperglycemic crises. Don't use the anion gap or urine ketones to decide DKA has resolved.
DKA severity (2024 consensus)
| Severity | pH / HCO₃⁻ | BHB | Mental status | Suggested care |
|---|---|---|---|---|
| Mild | pH >7.25 to <7.30 or HCO₃⁻ 15–18 mmol/L | 3.0–6.0 mmol/L | Alert | Ward or observation unit |
| Moderate | pH 7.0–7.25 or HCO₃⁻ 10 to <15 mmol/L | 3.0–6.0 mmol/L | Alert or drowsy | Step-down or intermediate care |
| Severe | pH <7.0 or HCO₃⁻ <10 mmol/L | >6.0 mmol/L | Stupor or coma | ICU |
Not every variable has to fit one row. Level of care is still a clinical decision.
Diagnosing diabetes (ADA 2026, outside an acute crisis)
| Test | Diabetes | Prediabetes |
|---|---|---|
| Fasting plasma glucose | ≥126 mg/dL (7.0 mmol/L) | 100–125 mg/dL (5.6–6.9 mmol/L) |
| 2-hr plasma glucose, 75 g OGTT | ≥200 mg/dL (11.1 mmol/L) | 140–199 mg/dL (7.8–11.0 mmol/L) |
| A1C | ≥6.5% | 5.7–6.4% |
| Random plasma glucose | ≥200 mg/dL (11.1 mmol/L) with classic symptoms or a hyperglycemic crisis | — |
Not from a meter, and usually not in the ED: Without unequivocal hyperglycemia, diabetes takes two abnormal results: two different tests, or one test repeated. A capillary meter value never makes the diagnosis. Stress hyperglycemia in acute illness needs outpatient follow-up, not a label.
A1C and average glucose: estimated average glucose (mg/dL) = 28.7 × A1C − 46.7. Treat it as a population estimate. Use the laboratory-reported eAG when you have it.
Management Priorities
Doses vary by protocol; follow local protocols and medical direction.
Sources don't agree on the cut-off. ADA sets its alert at <70 mg/dL. NASEMSO's model EMS guideline sets the line for symptomatic patients at ≤60 mg/dL. Follow local protocol.
Emergency: Hypoglycemia (<70 mg/dL with symptoms, or any low value with altered mental status)
- Can swallow and protect the airway: start with oral glucose (tablets or gel). Recheck at 15 min and keep repeating until glucose reaches ≥70 mg/dL. Finish with a meal or snack.
- Cannot swallow (Paramedic/RN/CCT): Use IV or IO dextrose, D10 preferred, in small steps, titrated to mental status. Without IV access, switch to glucagon IM, subcut or intranasal (EMT and AEMT per local protocol).
- Insulin pump: if the patient cannot take oral glucose and ALS is not available, stop the pump. Disconnect it or remove it at the insertion site. Otherwise, leave it running and treat.
- Recheck and prevent recurrence: Check glucose and mental status again. A D10 infusion and food come next after long-acting insulin or sulfonylureas. Octreotide treats sulfonylurea lows. Thiamine goes in before or with dextrose for at-risk patients (alcohol use, malnutrition, vomiting). Don't hold up dextrose to get it.
Emergency: DKA or HHS (2024 consensus, adults)
- Fluids: isotonic saline or a balanced crystalloid, 500–1,000 mL/hr for the first 2–4 hr, provided heart and kidney function allow. Use 250 mL boluses with reassessment in older adults, heart failure or dialysis.
- Potassium before insulin: K⁺ <3.5 mEq/L: replace it (10–20 mEq/hr) and hold insulin until K⁺ is above 3.5. K⁺ 3.5–5 mEq/L: add 20–30 mEq of K⁺ per liter of fluid. K⁺ above 5.0–5.2 mEq/L: skip potassium and recheck every 2 hr.
- Insulin (ED/ICU): Run fixed-rate IV regular insulin. When glucose reaches <250 mg/dL, add D5–D10 and cut the rate. Hold glucose at about 200 mg/dL until ketoacidosis resolves. In HHS, let glucose fall no faster than 90–120 mg/dL/hr.
- Monitor and repeat: Check glucose every 1–2 hr on a hospital meter. Repeat electrolytes, phosphate, creatinine, BHB and venous pH every 4 hr. Recheck K⁺ 2 hr after insulin starts. Bicarbonate isn't routine. Consider it only for severe acidosis, per protocol. Replace phosphate only if low. Children: follow the pediatric DKA protocol, since cerebral edema is the risk.
Medications
| Drug | Adult dose | Pediatric dose (max) | Onset / key notes |
|---|---|---|---|
| Oral glucose (tablets, gel) | 15–20 g PO (NASEMSO field dose: 25 g); repeat after 15 min if still <70 mg/dL | 0.3 g/kg PO for children with diabetes (ISPAD; 15 g above 50 kg); field protocols 0.5–1 g/kg; max 25 g | Only if able to swallow safely; follow with food |
| Dextrose 10% (D10) | 10 g (100 mL) IV/IO, or 5 g (50 mL) steps until alert; field max 25 g (250 mL) | 0.5–1 g/kg (5–10 mL/kg) IV/IO, max 25 g/dose; ISPAD in-hospital 2 mL/kg; neonate 2 mL/kg then infusion | Minutes; preferred at every age; recheck after each step |
| Dextrose 50% (D50) | 25 g (50 mL) slow IV into a large vein (D10 alternative) | Not under 8 yr (use D10; over 8 yr D25 2–4 mL/kg); max 25 g | High-alert Extravasation injury; overshoot hyperglycemia |
| Glucagon | 1 mg IM/subcut/IV, or 3 mg intranasal; one repeat after 15 min | 0.5 mg IM if under 20–25 kg (product-specific cut-off), 1 mg if heavier; intranasal 3 mg (age per product label); max 1 mg IM | Glucose rises within about 10 min; weak when glycogen is depleted (alcohol, starvation); vomiting |
| Octreotide (sulfonylurea hypoglycemia) | 50–100 mcg subcut (preferred) or IV every 6–12 hr as needed | 1–2 mcg/kg subcut or IV every 6–12 hr; max the adult dose | After dextrose correction; blocks insulin release. Observe 12–24 hr after dextrose and octreotide stop (longer in renal failure) |
| Thiamine | Prevention: 100 mg IV/IM; suspected Wernicke encephalopathy: 500 mg IV every 8 hr | Empiric 100 mg IV if deficiency suspected, then specialist dosing | Before or with dextrose when feasible; never delay dextrose |
| Insulin, regular IV (DKA/HHS) | DKA: 0.1 units/kg/hr; HHS without significant ketosis: 0.05 units/kg/hr, started only if glucose is not falling adequately with fluids alone and K⁺ is above 3.5 mEq/L; reduce to 0.05 units/kg/hr when glucose <250 mg/dL | DKA: 0.05–0.1 units/kg/hr, no bolus, started at least 1 hr after fluids begin | High-alert Start only when K⁺ is above 3.5 mEq/L; continue until ketoacidosis resolves |
| Isotonic crystalloid (0.9% saline or balanced) | 500–1,000 mL/hr for the first 2–4 hr; 250 mL boluses in frail or cardiac patients | Shock or hypovolemia (field): 10–20 mL/kg IV/IO bolus, reassess after each. DKA: 10 mL/kg over 30–60 min only if perfusion is impaired; no routine repeat boluses; follow the pediatric DKA protocol | Overly aggressive fluids risk cerebral edema in children |
| Potassium chloride IV (DKA/HHS) | K⁺ <3.5 mEq/L: 10–20 mEq/hr before insulin; K⁺ 3.5–5.0: 20–30 mEq per liter of fluid; above 5.0–5.2: none, recheck every 2 hr | Not routinely used without a protocol: per pediatric DKA protocol | High-alert Pump only; K⁺ at 2 hr, then every 4 hr |
High-alert drugs: Insulin, dextrose ≥20% and concentrated potassium are ISMP high-alert drugs. Order dextrose in grams. Have someone independently double-check insulin and potassium infusions on the pump.
Definitive care & disposition
- Transport or admit: sulfonylurea or long-acting insulin hypoglycemia, intentional overdose, hypoglycemia with seizure, no clear cause, or failure to recover after the field maximum dose.
- Release without transport (NASEMSO model, per protocol): only if repeat glucose is >80 mg/dL, mentation is normal without focal deficit, the patient takes insulin or metformin (no sulfonylurea), will eat now, a reliable adult stays, there are no other complaints and the cause is clear.
- ICU: Severe DKA, HHS, altered mental status, or a critical illness (sepsis, MI) call for it. Mild to moderate DKA can stay in the ED or step-down.
- Neonates: Symptomatic lows need IV dextrose and NICU care. So do lows despite feeding and dextrose gel.
Doses here are typical references. Follow your local protocols, medical direction and institutional policy.
Field & Transport Considerations
Point-of-care testing
A drop of capillary, venous or arterial whole blood goes in. A plasma-equivalent value comes out. The FDA expects hospital meters to land 95% of results within ±12 mg/dL of the lab value below 75 mg/dL, and within ±12% above it. Each meter is cleared only for the sample types and patients on its label. Follow the device instructions for the sequence:
- Indication: altered mental status, seizure, stroke symptoms, syncope, suspected intoxication, or diabetes with any acute illness.
- Prepare: gloves; meter quality control current; strips in date, from a closed container.
- Clean and dry the site: residue on the skin (sugar, alcohol not yet dry) changes the result.
- Sample: lance the side of a fingertip (heel in infants) and apply the drop to the strip as directed, or use a venous sample if the device is cleared for it.
- Record: the value, time, sample type and site, then repeat after every treatment and any change in mental status.
Before and during interfacility transport
Hand off the pre-treatment glucose and its time. Include the grams of dextrose or glucagon given, the insulin type and last dose, any sulfonylurea use and the pump status. On an insulin infusion, check glucose hourly and know the latest K⁺. A K⁺ under 3.5 mEq/L before insulin starts means insulin waits for potassium replacement.
| Setting | Consideration |
|---|---|
| Shock, severe dehydration, edema | Capillary results are unreliable; use a venous or arterial sample on a meter cleared for it, or a blood gas analyzer |
| Cold or hot vehicle, flight altitude | Strips and meters have labeled temperature and altitude limits; keep them in range |
| High-flow oxygen, anemia, polycythemia | Some strip chemistries read falsely high or low; check the device labeling |
Timing & Kinetics
| Parameter | Value | Clinical implication |
|---|---|---|
| Recheck after hypoglycemia treatment | 15 min | Repeat treatment until ≥70 mg/dL, then feed |
| Glucagon response | About 10 min (IM) | No response at 15 min: second dose and IV/IO dextrose |
| In vitro glycolysis, unseparated blood | 5–7% (about 10 mg/dL) per hr at room temperature | A delayed sample reads falsely low |
| Sulfonylurea half-life | Glipizide about 2–4 hr; glimepiride about 5–9 hr; glyburide and chlorpropamide longer | Hypoglycemia often lasts 12–24 hr or longer (renal failure prolongs it); observe 12–24 hr after dextrose and octreotide stop |
| Glucose in treated DKA | Falls below 250 mg/dL within 4–8 hr | Before ketoacidosis clears: add dextrose, keep insulin running |
| Glucose in treated HHS | Corrects over 8–10 hr | Fall no faster than 90–120 mg/dL/hr; osmolality 3–8 mOsm/kg/hr |
| Morning prednisone | Plasma peak about 1–2 hr; glucose effect lags | Glucose rises through the afternoon and peaks in the evening |
| Glucose checks on IV insulin | Every 30 min to 2 hr | Hourly is typical; more often after rate changes or a low |
Glucose normalizes before ketones do: In DKA, glucose reaches target hours before the acidosis clears. Don't mistake a normal number for a finished treatment. Never stop insulin because glucose is normal. Add dextrose instead.
Special Populations
| Population | What changes | Clinical implication |
|---|---|---|
| Neonates & infants | Glucose falls after birth and recovers over 72 hr; thresholds are lower in this transition; higher hematocrit can bias meters | Screen at-risk infants at 2 hr of age and every 3–6 hr before feeds; intervene below 47 mg/dL; use D10 only (never D50) |
| Children & adolescents | Same ranges as adults after the newborn period; symptoms may be behavioral (irritability, tantrums); DKA risks cerebral edema | Weight-based dextrose and glucagon; slower, protocol-based DKA fluids; one sulfonylurea tablet can cause hypoglycemia |
| Pregnancy | Gestational diabetes thresholds are lower (fasting ≥92 mg/dL on the one-step OGTT); DKA can occur with near-normal glucose | Check ketones and a venous gas in any pregnant patient with vomiting and tachypnea; A1C falls in normal pregnancy |
| Older adults | Reference range unchanged; HHS more common; more medications and kidney disease | Hypoglycemia may present as confusion or falls; smaller fluid boluses in DKA and HHS |
| CKD / dialysis | Slower insulin and sulfonylurea clearance; A1C distorted by anemia, transfusion and shortened red-cell survival | Prolonged hypoglycemia; trust measured glucose over A1C |
| Liver disease, alcohol use | Low glycogen stores and impaired gluconeogenesis | Fasting hypoglycemia; glucagon may fail: give dextrose and thiamine |
| SGLT2 inhibitor users | Ketoacidosis with glucose <200 mg/dL | Check ketones even when glucose is normal |
Continuous glucose monitors (CGM): many patients show up wearing one. The sensor reads interstitial fluid, so its number trails blood glucose. Confirm with a fingerstick or lab value before you treat a low or dose insulin.
Interfering Factors & Pitfalls
Collection & handling
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Delayed processing at room temperature | ↓ | Blood cells keep consuming glucose (5–7% per hr) | Citrate-buffered tube, or ice-water slurry and centrifuge within 15–30 min |
| Sodium fluoride (gray-top) tube alone | ↓ | Fluoride works slowly, so early glycolysis continues | Do not rely on fluoride alone; separate promptly |
| Sample drawn near a dextrose infusion | ↑ | Contamination with infusate | Draw from the other arm or below the infusion |
Medications & supplements
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Maltose, galactose or xylose (some IV immune globulins, icodextrin peritoneal dialysate) | False + | Some strip enzymes also read these sugars | Use a glucose-specific meter or the lab; a missed true low can be fatal |
| High blood oxygen tension | False − or unreliable | Oxygen interferes with some strip chemistries | Check the meter labeling; confirm with a blood gas or lab value |
Physiologic / biologic
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Low hematocrit (anemia) | False + on some meters | Hematocrit changes the plasma volume the strip sees | Confirm with lab glucose |
| High hematocrit (neonates, polycythemia) | False − on some meters | As above | Confirm a low result before labeling hypoglycemia, without delaying treatment |
| Shock, hypotension, severe dehydration, hypoxia, DKA, HHS | Unreliable | Poor capillary flow and altered blood chemistry | Venous or arterial sample, or laboratory glucose |
| Marked leukocytosis | ↓ | Extra cells consume glucose in the tube | Process immediately; citrate tube |
Common misinterpretations
- "Glucose is normal, so it is not DKA": euglycemic DKA (SGLT2 inhibitors, pregnancy) shows up with glucose <200 mg/dL. A normal-looking glucose doesn't rule it out.
- "Urine ketones are negative": the dipstick reads acetoacetate, not BHB. It underestimates early DKA. Measure blood BHB instead.
- "Plasma and whole blood are the same": at a normal hematocrit, plasma glucose reads about 11% higher than whole blood.
- "A1C tells me today’s glucose": A1C reflects about 3 months of glucose. It reads falsely low after blood loss, hemolysis, transfusion or in pregnancy. Iron deficiency can push it high.
Do not let doubt delay treatment: a surprising low in a well patient earns a repeat. A symptomatic patient gets treated first and confirmed afterward.
Physiology & Test Basics
What it measures
Glucose is the free sugar in plasma, or a plasma-equivalent value from whole blood on a meter or blood gas analyzer. The brain runs on it. It is also the most common bedside test in emergency care. A1C, β-hydroxybutyrate and urine glucose are separate tests. Each answers a different question.
Physiology & regulation
- Insulin: pulls glucose into muscle and fat, and it shuts down liver output.
- Counter-regulation: As glucose falls, insulin secretion stops first. Glucagon and epinephrine rise at 65–70 mg/dL. Cortisol and growth hormone follow.
- Fasting supply: The liver breaks down glycogen first, then runs gluconeogenesis. Alcohol, starvation and liver failure shut that down.
- Warning symptoms: Adrenergic symptoms show up first. Cognition fails below about 50 mg/dL. Recurrent lows blunt the warning, which is impaired awareness.
- Without insulin: Fat breaks down into ketones, mostly β-hydroxybutyrate, and that drives DKA. Partial insulin limits ketosis, so HHS shows up with extreme glucose and dehydration.
How it is measured
- Laboratory: venous plasma, preferably in a citrate-buffered tube. A gray-top (sodium fluoride/potassium oxalate) tube is the other option. Put it on ice and separate it within 15–30 min. Serum is acceptable if you separate it promptly. It runs as part of the BMP and CMP, with results in under an hour.
- Point of care: capillary, venous or arterial whole blood, read on a meter in seconds or on a blood gas analyzer.
- Fasting: a diagnostic fasting glucose needs at least 8 hr without calories.
Why it matters
Hypoglycemia can pass for stroke, seizure, intoxication or psychiatric illness. Caught early, it is fully reversible. Extreme hyperglycemia flags DKA and HHS. The glucose trend guides insulin, dextrose and potassium therapy in the ED, the ICU and during transport.
Clinical Pearls
Dawn phenomenon vs Somogyi: early-morning highs, about 4–8 AM, come from overnight counter-regulatory hormones. That is the dawn phenomenon. Rebound highs after a low overnight, the Somogyi effect, are largely disproven. Check a 2–3 AM glucose before you assume it.
Check the sugar in every altered patient: low sugar can look exactly like a stroke, a seizure or intoxication. Make the glucose check part of the first set of vitals for any of them, in the field and in the ED.
D10 in steps beats one D50 push: small D10 steps, titrated to mental status, wake patients as reliably as D50. You get less overshoot and no extravasation injury.
Hourly glucose on an insulin drip, and watch the K⁺: insulin pushes potassium into cells. Check K⁺ 2 hr after a DKA infusion starts. Recheck glucose 15 min after you treat any low.
Sulfonylurea lows come back: each dextrose bolus can trigger more insulin release. After the first correction, the fix is octreotide plus feeding or a dextrose infusion.
Alcohol and starvation empty the tank: with no glycogen to release, glucagon may fail. Give IV dextrose and thiamine. Expect a low glucose with ketosis, which is alcoholic ketoacidosis.
Steroid hyperglycemia peaks late: after morning prednisone, fasting glucose is often normal. The rise comes later. Check before lunch and dinner, when it shows.
Whipple triad confirms true hypoglycemia: you need all three: symptoms, a documented low plasma glucose, and relief once glucose is restored. Without diabetes, draw insulin, C-peptide and a sulfonylurea screen during the low, as long as that doesn't delay treatment.
A rising sodium in DKA is expected: as glucose falls, water moves back into cells and measured Na⁺ rises. That rise alone is no reason for hypotonic fluids. Follow the corrected sodium and osmolality.
References
- American Diabetes Association Professional Practice Committee for Diabetes. (2026). 2. Diagnosis and classification of diabetes: Standards of Care in Diabetes—2026. Diabetes Care, 49(Suppl 1), S27–S49. https://doi.org/10.2337/dc26-S002
- American Diabetes Association Professional Practice Committee for Diabetes. (2026). 16. Diabetes care in the hospital: Standards of Care in Diabetes—2026. Diabetes Care, 49(Suppl 1), S339–S355. https://doi.org/10.2337/dc26-S016
- Umpierrez, G. E., Davis, G. M., ElSayed, N. A., Fadini, G. P., Galindo, R. J., Hirsch, I. B., and colleagues. (2024). Hyperglycemic crises in adults with diabetes: a consensus report. Diabetes Care, 47(8), 1257–1275. https://doi.org/10.2337/dci24-0032
- Sacks, D. B., Arnold, M., Bakris, G. L., and colleagues. (2023). Guidelines and recommendations for laboratory analysis in the diagnosis and management of diabetes mellitus. Clinical Chemistry, 69(8), 808–868. https://doi.org/10.1093/clinchem/hvad080
- U.S. Food and Drug Administration. (2020). Blood glucose monitoring test systems for prescription point-of-care use: guidance for industry and Food and Drug Administration staff (issued September 29, 2020). https://www.fda.gov/media/119829/download
- National Association of State EMS Officials. (2022). National Model EMS Clinical Guidelines, Version 3.0: Hyperglycemia and Hypoglycemia. NASEMSO Medical Directors Council.
- Abraham, M. B., Karges, B., Dovc, K., and colleagues. (2022). ISPAD Clinical Practice Consensus Guidelines 2022: Assessment and management of hypoglycemia in children and adolescents with diabetes. Pediatric Diabetes, 23(8), 1322–1340. https://doi.org/10.1111/pedi.13443
- Narvey, M. R., & Marks, S. D. (2019). The screening and management of newborns at risk for low blood glucose (Canadian Paediatric Society position statement). Paediatrics & Child Health, 24(8), 536–544. https://doi.org/10.1093/pch/pxz134
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