RN Basics

One-Pager

Lab Values to Know

Normal ranges in US units, therapeutic drug levels, and acting on a critical result

Reviewed by Alex G, BSN, RN, CEN, CCRN, CMC, NREMT-P · Checked against current sources October 2026

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Blood counts and clotting

Study summary, not a bedside tool. Labs vary: use the printed range, the trend and your protocols.

TestNormalExam clue
WBC4,500–11,000/mm³ANC under 500: neutropenic precautions
HgbM 14–18; F 12–16 g/dLFalls with bleeding; trend it
HctM 42–50%; F 37–47%Moves with Hgb
Platelets150,000–400,000/mm³Under 20,000: spontaneous bleeding risk
PT / INR11–13.5 s / 0.8–1.1Warfarin monitoring
aPTT25–35 sHeparin: 1.5–2 × control (many texts 1.5–2.5) or anti-Xa
Valve type and clot risk can change targets.
Warfarin indicationTarget INR
VTE, AF, bileaflet mechanical aortic valve2.0–3.0 (goal 2.5)
Mechanical mitral or caged-ball valve2.5–3.5 (goal 3.0)

Chemistry panel

TestNormalExam clue
Sodium135–145 mEq/LLow/high: confusion, seizures
Potassium3.5–5.0 mEq/LLow/high: arrhythmias; ECG
Chloride98–107 mEq/LLow with vomiting
HCO₃⁻ (CO₂)23–29 mEq/LLow: metabolic acidosis
BUN6–20 mg/dLUp: AKI, dehydration, GI bleed
Creatinine0.6–1.3 mg/dLUp: AKI; renal dosing (F lower)
Glucose (fast)70–99 mg/dLUnder 70: low; 126+: diabetes
Calcium8.8–10.3 mg/dLCorrect for low albumin
Magnesium1.7–2.2 mg/dLLow Mg keeps K low
Phosphorus2.8–4.5 mg/dLHigh in CKD, with low Ca
Albumin3.4–5.4 g/dLLow: edema, malnutrition

Low albumin lowers total Ca and raises free phenytoin. Many books use Ca 9.0–10.5, Mg 1.3–2.1 mEq/L: use the range the item prints.

Diabetes, lipids, liver, heart

TestNormalExam clue
A1CUnder 5.7%6.5%+: diabetes; goal often <7%
CholesterolUnder 200 mg/dLFast 9–12 h only if ordered
LDLUnder 100 mg/dL"Bad" cholesterol
HDL60+ mg/dL bestLow: under 40 (men), 50 (women)
TriglyceridesUnder 150 mg/dLVery high: pancreatitis risk
ALT / ASTALT 4–36; AST 8–33 U/LUp: liver injury (acetaminophen)
BNPUnder 100 pg/mLHigher: HF likelier, worse
Troponin≤ lab's 99th percentileRise/fall above 99th + ischemia = MI

A1C 5.7–6.4%: prediabetes; it reflects about 3 months, skewed by anemia, kidney failure and transfusion. Troponin up without ischemia is injury, not MI. hs-troponin is serial (often 0 and 1–2 h); STEMI does not wait for it.

ABG normals

The ABG Interpretation one-pager gives the steps.
ValueNormal
pH7.35–7.45
PaCO₂35–45 mm Hg
HCO₃⁻22–26 mEq/L
PaO₂80–100 mm Hg (room air; some labs 75–100)
SaO₂95–100%

Therapeutic drug levels

Draw digoxin just before a dose or 6+ h after; lithium 12 h after the last dose.
DrugRangeToxicity clues
Digoxin0.5–2.0 ng/mL; heart failure often 0.5–0.9Nausea, yellow-green vision, bradycardia, arrhythmias
Lithium0.8–1.2 mEq/L acute; 0.8–1.0 maintenanceToxic 1.5+. Early: vomiting, diarrhea, weakness, poor coordination. Later: ataxia, slurred speech, confusion, seizures
Phenytoin10–20 mcg/mL (free 1–2)Nystagmus near 20, ataxia near 30, lethargy over 40
VancomycinAUC 400–600 mg·h/L (MIC 1) for serious MRSAKidney injury: rising creatinine, low urine output

Critical result: nurse actions

  1. Assess now: vital signs, symptoms, ECG if K or digoxin.
  2. Check range and trend; question an odd result (hemolyzed K, drawn above an IV).
  3. Act per protocol: hold the related drug, start precautions, monitor.
  4. Notify the provider (SBAR); read back phoned results.
  5. Document value, time, who was told, orders and response.
  6. LPN/LVN: collect data and report to the RN or provider.
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Related one-pagers

Sources

  1. American Board of Internal Medicine. ABIM Laboratory Test Reference Ranges, January 2026. Link
  2. NBME. Laboratory Values. Link
  3. MedlinePlus Medical Encyclopedia. Basic metabolic panel (BMP). Reviewed 1/1/2025. Link
  4. MedlinePlus Medical Encyclopedia. Complete blood count (CBC). Reviewed 10/14/2024. Link
  5. MedlinePlus Medical Encyclopedia. Hemoglobin. Reviewed 2/27/2026. Link
  6. MedlinePlus Medical Encyclopedia. Potassium test. Reviewed 5/19/2025. Link
  7. MedlinePlus Medical Encyclopedia. Chloride test - blood. Updated 5/19/2025. Link
  8. MedlinePlus Medical Encyclopedia. BUN - blood test. Reviewed 5/19/2025. Link
  9. MedlinePlus Medical Encyclopedia. Creatinine blood test. Reviewed 7/13/2025. Link
  10. MedlinePlus Medical Encyclopedia. Albumin - blood (serum) test. Reviewed 2/13/2025. Link
  11. MedlinePlus Medical Encyclopedia. Calcium blood test. Reviewed 11/6/2025. Link
  12. MedlinePlus Medical Encyclopedia. Magnesium blood test. Reviewed 2/13/2025. Link
  13. MedlinePlus Medical Encyclopedia. Phosphorus blood test. Reviewed 11/6/2025. Link
  14. Grundy SM, et al. 2018 AHA/ACC Guideline on the Management of Blood Cholesterol. Circulation. 2019;139(25):e1082-e1143. Link
  15. MedlinePlus Medical Encyclopedia. Prothrombin time (PT). Reviewed 2/3/2025. Link
  16. MedlinePlus Medical Encyclopedia. Partial thromboplastin time (PTT). Reviewed 2/3/2025. Link
  17. MedlinePlus Medical Encyclopedia. Alanine transaminase (ALT) blood test. Updated 1/1/2025. Link
  18. MedlinePlus Medical Encyclopedia. Aspartate aminotransferase (AST) blood test. Reviewed 1/1/2025. Link
  19. MedlinePlus Medical Encyclopedia. Brain natriuretic peptide (BNP) test. Updated 7/14/2024. Link
  20. MedlinePlus Medical Encyclopedia. Hemoglobin A1C (HbA1c) test. Updated 5/18/2026. Link
  21. CDC. A1C Test for Diabetes and Prediabetes. Link
  22. CDC. Diabetes Testing. Link
  23. NIDDK. Low Blood Glucose (Hypoglycemia). Reviewed July 2021. Link
  24. MedlinePlus. Cholesterol Levels: What You Need to Know. Updated 8/20/2026. Link
  25. MedlinePlus Medical Encyclopedia. Triglyceride level. Reviewed 7/14/2024. Link
  26. MedlinePlus Lab Tests. Arterial Blood Gas (ABG) Test. Updated 6/26/2025. Link
  27. Merck Manual Professional. Hypocalcemia. Full review Jun 2025. Link
  28. Merck Manual Professional. Hypercalcemia. Full review Jun 2025. Link
  29. Merck Manual Professional. Hypomagnesemia. Updated Jun 2025. Link
  30. Merck Manual Professional. Hypermagnesemia. Updated Dec 2025. Link
  31. Merck Manual Professional. Hypophosphatemia. Updated Dec 2025. Link
  32. Merck Manual Professional. Hyperphosphatemia. Updated Dec 2025. Link
  33. Merck Manual Professional. Hypokalemia. Updated Dec 2025. Link
  34. Merck Manual Professional. Overview of Platelet Disorders. Updated Jun 2026. Link
  35. Merck Manual Professional. Thrombocytopenia: Other Causes (heparin-induced thrombocytopenia). Full review Jun 2026. Link
  36. Cuker A, et al. American Society of Hematology 2018 guidelines for management of venous thromboembolism: heparin-induced thrombocytopenia. Blood Adv. 2018;2(22):3360-3392. Link
  37. Merck Manual Professional. Neutropenia. Updated Apr 2026. Link
  38. Thygesen K, et al. Fourth universal definition of myocardial infarction (2018). Eur Heart J. 2019;40(3):237-269. Link
  39. Byrne RA, et al. 2023 ESC Guidelines for the management of acute coronary syndromes. Eur Heart J. 2023;44(38):3720-3826. Link
  40. LANOXIN (digoxin) tablets prescribing information. DailyMed, revised Dec 2024. Link
  41. van Veldhuisen DJ, et al. Low-dose digoxin in patients with heart failure with reduced or mildly reduced ejection fraction (DECISION). Nat Med. 2026. Link
  42. WisTech Open. Nursing Pharmacology, 2nd ed. (2023, CC BY 4.0), 6.7 Cardiac Glycosides. Link
  43. Lithium carbonate capsules prescribing information (Camber). DailyMed, revised Dec 2022. Link
  44. Lithium carbonate capsules prescribing information (Alembic). DailyMed, older-format label. Link
  45. DILANTIN (extended phenytoin sodium) capsules prescribing information. DailyMed, revised Aug 2023. Link
  46. ASHP/IDSA/PIDS/SIDP. Revised consensus guideline for therapeutic monitoring of vancomycin for serious MRSA infections (Rybak MJ, et al., 2020). Link
  47. Heparin Sodium Injection prescribing information (Fresenius Kabi). DailyMed, revised 10/2021. Link
  48. JANTOVEN (warfarin sodium) prescribing information. DailyMed, revised Sept 2017. Link
  49. AHRQ PSNet. Communication Between Clinicians (Primer). Link