BMP

Background

  • The basic metabolic panel (BMP) is the workhorse lab test in emergency medicine — a panel of 8 blood chemistries that assesses electrolyte balance, renal function, acid-base status, and blood glucose.
  • It is one of the most frequently ordered tests in the ED and provides rapid, actionable data across virtually every acute presentation.[1]


Components and Normal Ranges

Component Normal Range What It Assesses
Sodium (Na) 136–145 mEq/L Fluid balance, osmolality
Potassium (K) 3.5–5.0 mEq/L Cardiac conduction, neuromuscular function
Chloride (Cl) 98–106 mEq/L Acid-base balance (with bicarb)
Bicarbonate (CO2) 22–30 mEq/L Acid-base status
BUN 7–20 mg/dL Renal function, hydration status
Creatinine (Cr) 0.7–1.3 mg/dL Renal function (GFR estimation)
Glucose 70–100 mg/dL (fasting) Metabolic/endocrine status
Calcium (Ca) 8.5–10.5 mg/dL Neuromuscular, cardiac, bone
  • Reference ranges vary by lab — always use your institution's values
  • Most labs also report a calculated anion gap and eGFR with the BMP
  • BMP vs. CMP: A comprehensive metabolic panel (CMP) includes all 8 BMP components plus albumin, total protein, total bilirubin, ALP, ALT, and AST. Order a CMP when liver assessment is also needed

Anion Gap

  • Anion gap = Na − (Cl + HCO3)
  • Normal: 8–12 mEq/L (varies by lab; some use 3–11)
  • Always calculate the anion gap when reviewing a BMP — it is the single most important derived value in the ED
  • Elevated anion gap with metabolic acidosis → differential includes: MUDPILES (Methanol, Uremia, DKA, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates)
  • Correct the anion gap for albumin if the patient is hypoalbuminemic: Corrected AG = Calculated AG + 2.5 × (4.0 − measured albumin). A "normal" anion gap in a hypoalbuminemic patient may actually be elevated

Clinical Features

The BMP is not ordered based on specific clinical features of the panel itself — it is ordered as a foundational assessment in most acute presentations. The BMP is appropriate in virtually any ED patient being evaluated for:

Differential Diagnosis

The BMP does not generate a single differential — each abnormal component points to its own set of diagnoses. The following are the most ED-relevant abnormalities:

Sodium

  • Hyponatremia (<136): Volume depletion, SIADH, heart failure, cirrhosis, psychogenic polydipsia, medications (thiazides, SSRIs), adrenal insufficiency, hypothyroidism, beer potomania
  • Hypernatremia (>145): Dehydration, diabetes insipidus, osmotic diuresis, insensible losses, inadequate free water intake (elderly, altered patients)

Potassium

  • Hyperkalemia (>5.0): Renal failure, rhabdomyolysis, acidosis, medications (ACEi/ARBs, K-sparing diuretics, TMP-SMX), hemolysis (spurious), adrenal insufficiency, tumor lysis syndrome
  • Hypokalemia (<3.5): GI losses (vomiting, diarrhea), diuretics, renal tubular acidosis, hypomagnesemia, DKA treatment, alkalosis

Bicarbonate

  • Low HCO3 (<22): Metabolic acidosis — calculate anion gap to differentiate AGMA from non-anion-gap metabolic acidosis (NAGMA)
  • High HCO3 (>30): Metabolic alkalosis (vomiting, diuretics, volume contraction), chronic respiratory acidosis compensation

BUN/Creatinine

  • Elevated BUN and Cr: Acute kidney injury (prerenal, intrinsic, postrenal), chronic kidney disease, dehydration
  • Elevated BUN with normal Cr (high BUN:Cr ratio >20:1): Prerenal azotemia (dehydration, CHF, GI bleed), high-protein diet, catabolic state, upper GI hemorrhage, corticosteroids
  • Low BUN: Malnutrition, liver disease, overhydration

Glucose

  • Hyperglycemia (>200): DKA, HHS, stress response, steroid use, new-onset diabetes, sepsis
  • Hypoglycemia (<70): Insulin/sulfonylurea use, sepsis, liver failure, adrenal insufficiency, alcohol, malnutrition

Calcium

  • Hypercalcemia (>10.5): Malignancy, hyperparathyroidism, granulomatous disease, immobilization, thiazides, vitamin D toxicity, milk-alkali syndrome
  • Hypocalcemia (<8.5): Hypoparathyroidism, vitamin D deficiency, pancreatitis, rhabdomyolysis, massive transfusion (citrate), chronic kidney disease, hypomagnesemia, sepsis
  • Always correct calcium for albumin: Corrected Ca = Measured Ca + 0.8 × (4.0 − albumin)

Evaluation

Workup

  • BMP is drawn as a venous blood sample (green-top lithium heparin tube or red/gold-top serum tube depending on institution)
  • Results typically available within 30–60 minutes in most ED laboratories
  • Point-of-care (POC) devices (e.g., i-STAT) can provide electrolytes, glucose, BUN, and creatinine in minutes from a single drop of blood — particularly useful in resuscitation, cardiac arrest, and critical care settings
  • Hemolyzed specimens falsely elevate potassium (K leaks from lysed RBCs) — if potassium is unexpectedly high in a stable patient, repeat with a non-hemolyzed specimen before treating

Diagnosis

  • The BMP is a screening and monitoring tool, not a definitive diagnostic test
  • Abnormalities should be interpreted in clinical context and often require additional testing (e.g., VBG/ABG for acid-base workup, osmolality for hyponatremia, PTH for calcium disorders, urinalysis for AKI evaluation)
  • Serial BMPs are essential for monitoring electrolyte replacement, DKA management, AKI trends, and response to diuretic therapy

Management

Management is directed at the specific abnormality identified. The most time-critical BMP findings in the ED include:

  • Hyperkalemia >6.0 mEq/L: ECG immediately → calcium gluconate for membrane stabilization → insulin + glucose, albuterol for intracellular shift → kayexalate/patiromer for elimination → consider emergent dialysis
  • Hypoglycemia <70 mg/dL: D50W IV (or oral glucose if alert); identify and treat cause
  • Severe hyponatremia <120 mEq/L: Risk of cerebral edema and seizure; hypertonic saline (3% NaCl) if symptomatic; correct slowly (≤8–10 mEq/L in 24 hours) to avoid osmotic demyelination
  • Diabetic ketoacidosis: Insulin drip, aggressive IV fluids, potassium replacement, close monitoring with serial BMPs every 1–2 hours
  • Anion gap metabolic acidosis: Identify and treat underlying cause (see MUDPILES); consider toxic alcohol workup (osmolar gap, specific levels) if unexplained elevated AG
  • Acute kidney injury: Volume resuscitation (if prerenal), identify and treat cause, avoid nephrotoxins, consider emergent dialysis for refractory hyperkalemia, acidosis, or volume overload

Disposition

  • Disposition depends on the specific abnormality and clinical context, not the BMP result in isolation
  • Admit for: Severe electrolyte derangements requiring IV correction or continuous monitoring, DKA/HHS, AKI with rising creatinine or need for dialysis, symptomatic hyponatremia, hyperkalemia unresponsive to ED treatment
  • Discharge with close follow-up for: Mild electrolyte abnormalities that are corrected in the ED, stable chronic kidney disease with known baseline, incidental mild hypo/hyperglycemia with outpatient management plan
  • Repeat BMP before discharge when electrolytes have been repleted in the ED (e.g., after potassium or magnesium replacement) to confirm adequate correction

See Also

External Links

References

  1. ↑ Basic Metabolic Panel (BMP).
    • MedlinePlus Lab Tests.
    • Accessed 2025.
This page is issued from WikEM. The text is available under an unknown license unless otherwise noted. Additional terms may apply for the media files.