At a Glance

Use It For
Deciding the first action when a critical lab value is called in for an adult patient.
Fastest Answer
Symptoms or ECG changes come first: treat the patient, then confirm the value. Potassium with ECG changes gets IV calcium at once; a K⁺ of 6.5 or more with a normal ECG still gets urgent shifting therapy.
Key Numbers
  • K⁺ <2.5 or ≥6.5 mEq/L
  • Glucose <50 or >450 mg/dL
  • pH <7.20 or >7.60
  • Hgb <7 g/dL; INR >5
Don't Miss
A normal ECG does not exclude dangerous hyperkalemia: a K⁺ of 6.5 or more needs urgent treatment in kidney disease or acidosis. Overly rapid sodium correction can cause osmotic demyelination.
Verify Locally
Your laboratory's critical call list, call interval and pediatric or pregnancy intervals set the thresholds. Local protocol and medical direction override this table.

Reference Table

These are typical adult values, and your lab sets the real cutoffs. This table is not a full call list. Coagulation beyond INR, WBC or ANC, blood gas partial pressures, ionized calcium, troponin and drug levels all vary by lab, so they stay out of this table.

TestCritical LowCritical HighImmediate Action
Potassium (K⁺)
<2.5 mEq/L
≥6.5 mEq/L, or any hyperkalemic ECG change
Low: cardiac monitoring; replace per protocol (potassium chloride). Never give IV potassium by push; infusion rates are set by protocol, with lower limits for peripheral lines than central lines and continuous ECG monitoring. Check and replace magnesium. High: ECG changes mean give IV calcium to stabilize the myocardium now. A K⁺ of 6.5 or more with a normal ECG still needs urgent shifting therapy and monitoring if there is kidney disease, acidosis, tissue breakdown or a rising trend. Repeat on a non-hemolyzed sample only when pseudohyperkalemia is likely (hemolysis, thrombocytosis or leukocytosis, no risk factors), and never let the repeat delay treatment. Shift K⁺ with insulin plus dextrose, and check glucose hourly for at least 4 to 6 hours afterward (hypoglycemia risk is highest in kidney failure; lower the insulin dose per protocol). Add nebulized albuterol as an adjunct. Sodium bicarbonate helps mainly when there is metabolic acidosis. Then remove K⁺ (dialysis for refractory cases).
Sodium (Na⁺)
<120 mEq/L
>160 mEq/L
Low with severe symptoms (seizure, coma, respiratory compromise): hypertonic saline per protocol (3% saline), with a protocol-set correction limit and frequent sodium checks, because rapid correction of chronic hyponatremia can cause osmotic demyelination. High: identify the cause and correct the free-water deficit gradually, per protocol.
Calcium, total (Ca²⁺)
<6 mg/dL
>13 mg/dL
Low: ECG and QT check; IV calcium per protocol (calcium gluconate or calcium chloride). Calcium chloride is a vesicant: give it slowly through a secure large vein or central line, and use caution in patients taking digoxin, with ECG and calcium monitoring. Check magnesium, albumin and ionized calcium. High: hydration, stop calcium and vitamin D sources, check PTH and the cause, per protocol.
Magnesium (Mg²⁺)
<1 mg/dL
Lab-specific; toxicity signs need a call regardless of the number
Low: IV magnesium per protocol (magnesium sulfate); watch for ECG changes and arrhythmia. High: stop magnesium sources, assess reflexes, breathing and rhythm, and give IV calcium per protocol.
Glucose
<50 mg/dL
>450 mg/dL
Low: treat at once, whether or not symptoms are present (oral glucose if the patient can swallow, IV dextrose if not); do not wait for a repeat result. High: check for DKA or HHS (ketones, osmolality, mental status); ICU care for severe disease.
Arterial pH
<7.20
>7.60
Assess the respiratory and metabolic components with the PaCO₂ and HCO₃⁻; treat the cause and ventilation problem. Bicarbonate use is protocol-dependent (sodium bicarbonate).
Hemoglobin (Hgb)
<7 g/dL
>20 g/dL
Low: bleeding control and transfusion per threshold and clinical status (red blood cells). Restrictive threshold of 7 g/dL for hemodynamically stable hospitalized adults; AABB 2023 allows 7.5 g/dL for cardiac surgery and 8 g/dL for orthopedic surgery or pre-existing cardiovascular disease. Active bleeding or instability is treated on clinical status, not a number. High: check for hemoconcentration or lab error; hematology evaluation per protocol.
Platelet count
<30 ×10³/µL (lab-specific; many labs call below 20)
>1,000 ×10³/µL
Low: assess for bleeding; platelet transfusion per hematology and protocol, but avoid empiric platelet transfusion when TTP or HIT is suspected, since it can worsen thrombosis. High: assess for thrombosis or bleeding; hematology per protocol.
PT/INR
None set
>5
Hold the anticoagulant and confirm the cause: warfarin effect versus liver disease, DIC, sepsis or a DOAC effect. For major bleeding on a vitamin K antagonist, reversal per protocol with 4-factor PCC and vitamin K; PCC carries a boxed warning for arterial and venous thromboembolism.
Lactate
None set
≥4 mmol/L
Assess for hypoperfusion and sepsis, and look for other causes of high lactate (seizure, epinephrine or beta-agonists, metformin, liver failure, mesenteric ischemia). If septic shock or high-probability sepsis is suspected, give antimicrobials within 1 hour; if sepsis without shock is possible, reassess and give them within 3 hours if concern persists. Repeat lactate to guide resuscitation (Surviving Sepsis Campaign 2021).

How to Use & Interpret
  1. Confirm the result is real. Check for hemolysis, delayed processing and point-of-care versus lab differences before acting on an extreme value, but never delay treatment of a symptomatic patient to repeat it.
  2. Match the threshold to your lab. The numbers in the table are typical adult values. The lab that issued the result sets the call list and the call interval.
  3. Act on the patient first. A critical value in an unstable patient is treated with the same urgency as the monitor, and the ECG, glucose and rhythm are checked at the bedside.
  4. Repeat and trend. Re-check the same analyte after treatment (for example potassium after shifting therapy, or lactate after fluid resuscitation), and link to the acid-base interpretation page when pH, PaCO₂ and HCO₃⁻ disagree.
Institutions set their own limits: Federal lab rules require the lab to alert the responsible person right away for panic or life-threatening results (42 CFR 493.1291). Each accredited hospital writes its own policy: what counts as critical, who the responsible clinician is and how fast results get reported. The Joint Commission reorganized its patient safety goals into National Performance Goals in 2026. Every value on this page is a typical adult limit. The local lab's call list is the one that governs.

Special Populations
  • Pediatrics: Kids are not small adults. Limits shift with age, most of all for glucose, hemoglobin and platelets. Use the lab's pediatric and neonatal intervals, and don't apply adult limits to a neonate. For drug doses, see weight-based dosing.
  • Pregnancy: Pregnancy lowers hemoglobin. Plasma expands, so the number drops, and platelet counts shift near term. Use pregnancy-specific intervals and involve the obstetric team. Magnesium levels matter during magnesium sulfate therapy for preeclampsia.
  • Older Adults: Many older patients start with some kidney impairment, so potassium and magnesium build up faster. Thiazide, ACE-inhibitor and ARB therapy all raise hyperkalemia risk. Thiazides also raise hyponatremia risk. Hypoglycemia symptoms may be blunted, so treat a low glucose on the number, not the symptoms alone.
  • Renal Impairment: In kidney failure, potassium and magnesium pile up. A dialysis patient who misses a session can walk in with hyperkalemia (KDIGO 2020 Controversies Conference).

Pitfalls & Safety Checks
  • Error: Calling a high potassium pseudohyperkalemia because the ECG looks fine, then waiting on a redraw. Treat first when the value fits the picture, confirm in parallel and check the ECG.
  • Error: One lab threshold for every patient. Kids, pregnant patients and neonates each have their own intervals.
  • Error: Waiting on a glucose result in a symptomatic patient with a low point-of-care reading. Treat first, confirm second. Asymptomatic lows get treated too.
  • Error: Raising sodium too fast. Correct chronic hyponatremia too quickly and you can cause osmotic demyelination (expert panel recommendations, 2013).
  • Error: Reversing an INR above 5 in someone who isn't bleeding. Hold the drug and find the cause. Save PCC for major or life-threatening bleeding on a vitamin K antagonist.

Field & Transport Considerations
  • EMS and transport: Lab values often aren't available in the field. Ask the receiving facility for the last results and the calls they expect. Carry point-of-care glucose and ECG monitoring with you.
  • Handoff: Say what the critical value was, when the call came in, what you already gave and whether a repeat sample went out. The details vary by state and agency protocol.

Clinical Pearls
Discriminator: Peaked T waves with a potassium of 6.5? IV calcium now. Normal ECG, potassium of 6.5? Still urgent shifting therapy and monitoring if there's kidney disease, acidosis or a rising trend. The ECG sets how urgently calcium is given. It doesn't decide whether you treat. A normal tracing does not rule out arrhythmia risk.
Glucose: A confirmed glucose under 70 mg/dL gets treated right away. Symptoms or not. The 2017 international position statement splits it up: level 2 is under 54 mg/dL, and level 1 runs from 54 to under 70 mg/dL.
Lactate: A lactate of 4 mmol/L or higher gets called in most labs. Plenty of causes have nothing to do with sepsis. Repeat it to see whether treatment is working.

Related

References
  1. Centers for Medicare & Medicaid Services. (2026). 42 CFR 493.1291, Standard: Test report (laboratory alert for panic or imminently life-threatening results). Code of Federal Regulations. https://www.ecfr.gov/api/versioner/v1/full/2026-10-01/title-42.xml?part=493&section=493.1291
  2. Evans, L., Rhodes, A., Alhazzani, W., et al. (2021). Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021. Critical Care Medicine, 49(11), e1063–e1143. https://doi.org/10.1097/CCM.0000000000005337
  3. Carson, J. L., Stanworth, S. J., Guyatt, G., et al. (2023). Red Blood Cell Transfusion: 2023 AABB International Guidelines. JAMA. https://doi.org/10.1001/jama.2023.12914
  4. Umpierrez, G. E., Davis, G. M., ElSayed, N. A., et al. (2024). Hyperglycemic Crises in Adults With Diabetes: A Consensus Report. Diabetes Care. https://doi.org/10.2337/dci24-0032
  5. International Hypoglycaemia Study Group. (2017). Glucose Concentrations of Less Than 3.0 mmol/L (54 mg/dL) Should Be Reported in Clinical Trials: A Joint Position Statement of the American Diabetes Association and the European Association for the Study of Diabetes. Diabetes Care. https://doi.org/10.2337/dc16-2215
  6. Verbalis, J. G., Goldsmith, S. R., Greenberg, A., et al. (2013). Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. The American Journal of Medicine. https://doi.org/10.1016/j.amjmed.2013.07.006
  7. Clase, C. M., Carrero, J. J., Ellison, D. H., et al. (2020). Potassium homeostasis and management of dyskalemia in kidney diseases: conclusions from a KDIGO Controversies Conference. Kidney International. https://doi.org/10.1016/j.kint.2019.09.018
  8. Tomaselli, G. F., Mahaffey, K. W., Cuker, A., et al. (2020). 2020 ACC Expert Consensus Decision Pathway on Management of Bleeding in Patients on Oral Anticoagulants. Journal of the American College of Cardiology. https://doi.org/10.1016/j.jacc.2020.04.053
  9. Kcentra (prothrombin complex concentrate, human) prescribing information. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=eee1afb8-324c-42e4-8bf0-f0c9da5e6d42
  10. Calcium chloride injection prescribing information. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d5d9c301-599e-47bb-ba9b-c0065c08dfb4

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  • For Educational Purposes Only: This content is intended for educational reference and should not be used for clinical decision-making.
  • Not a Substitute for Professional Judgment: Always consult your local protocols, institutional guidelines, and supervising physicians.
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