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.

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:

• Altered mental status, syncope, weakness, seizure
• Nausea, vomiting, diarrhea, dehydration
• Chest pain, dyspnea, cardiac arrest
• DKA, HHS, hypoglycemia
• Acute kidney injury, chronic kidney disease
• Drug overdose/toxicologic emergency
• Sepsis, shock
• Medication monitoring (diuretics, ACEi/ARBs, digoxin, lithium, metformin)
• Trauma (as part of initial laboratory panel)

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

• Hyperkalemia
• Hyponatremia
• Hypoglycemia
• Diabetic ketoacidosis
• Acute kidney injury
• Metabolic acidosis
• Hypercalcemia
• Rhabdomyolysis

External Links

• MedlinePlus: Basic Metabolic Panel