BMP Blood Test (Basic Metabolic Panel) Explainer

What is a BMP blood test?

A basic metabolic panel (BMP) is a group of eight blood tests run together on one sample. It gives a quick snapshot of your body's chemistry: blood sugar, salt and water balance, acid–base balance, kidney function and calcium. It is one of the most common blood tests in clinics, emergency departments and hospitals, often ordered as "BMP labs", "chem 7" (an older name for seven of the eight tests) or "U&Es" (urea and electrolytes) in the UK, which covers a similar subset.

The eight BMP tests are:

1. Glucose – blood sugar.
2. Sodium (Na) – the main salt in the blood, closely linked to water balance.
3. Potassium (K) – essential for nerve and muscle function, including the heart.
4. Chloride (Cl) – travels with sodium and helps maintain acid–base balance.
5. Bicarbonate (HCO₃⁻, often reported as CO₂ or total CO₂) – the main buffer against acid.
6. Blood urea nitrogen (BUN) – a waste product of protein metabolism cleared by the kidneys.
7. Creatinine – a waste product of muscle metabolism and the basis of eGFR.
8. Calcium (Ca) – needed for bones, nerves, muscles and clotting.

The explainer above lets you enter any or all of these values (in US or SI units) and shows how each compares with typical adult reference ranges. It also calculates three useful derived values – the anion gap, the BUN/creatinine ratio and an estimated serum osmolality – and flags values far enough outside the range to need prompt attention.

BMP normal ranges

These ranges are from the NBME laboratory reference values. Every laboratory sets its own range, and the one printed next to your result is the one to use. For sodium, potassium, chloride and bicarbonate, mEq/L and mmol/L give the same number, because each ion carries a single charge.

BMP vs CMP vs CBC

If your panel included liver tests, see the ALT blood test page, and for blood cells see the CBC blood test.

Each BMP test explained

Glucose

Glucose is the body's main fuel. A fasting value of 70–99 mg/dL is normal; 100–125 mg/dL is in the prediabetes range; 126 mg/dL or more on two occasions meets the American Diabetes Association criterion for diabetes. Many BMPs are not taken fasting, so a single high value after a meal is not unusual. A low glucose (under 70 mg/dL) can cause shakiness, sweating or confusion, and below 54 mg/dL is considered clinically significant hypoglycaemia. To understand long-term glucose, the A1C calculator and chart is more useful than a single glucose value.

Sodium

Sodium mostly reflects water balance rather than salt intake. Low sodium (hyponatraemia), below 136 mEq/L, is the most common electrolyte abnormality in hospital and often comes from extra water relative to sodium – due to diuretics (especially thiazides), heart, liver or kidney disease, some antidepressants, vomiting, very high water intake, or a hormone imbalance called SIADH. High sodium (hypernatraemia) usually means too little water, from dehydration, fever or not being able to drink. Severe or rapidly changing sodium can cause confusion and seizures, and because of the risks of correcting it too fast, it is always managed medically. If glucose is very high, sodium appears falsely low – the corrected sodium calculator adjusts for that.

Potassium

Potassium must stay in a tight range because it controls the electrical activity of nerves and the heart. Low potassium is common with diuretics, vomiting and diarrhoea, and can cause muscle weakness, cramps and abnormal heart rhythms. High potassium can result from kidney disease, some blood-pressure medicines (ACE inhibitors, ARBs, spironolactone), potassium supplements and severe tissue damage – but the most common reason for a high potassium result is haemolysis: red cells breaking in the tube during a difficult draw, releasing potassium. Labs usually comment on haemolysis, and a surprising high potassium is often repeated promptly. Very high or very low potassium can be dangerous and needs urgent attention.

Chloride

Chloride usually moves with sodium. Low chloride is seen with prolonged vomiting (loss of stomach acid) and with low sodium. High chloride occurs with dehydration, large volumes of saline fluid and some types of metabolic acidosis, such as from diarrhoea or certain kidney tubule problems.

Bicarbonate (CO₂)

On a BMP, "CO₂" means total carbon dioxide, which is mostly bicarbonate, not the gas measured in a blood-gas test. Low bicarbonate indicates a metabolic acidosis (for example diabetic ketoacidosis, kidney failure, severe diarrhoea, lactic acidosis) or compensation for over-breathing. High bicarbonate indicates a metabolic alkalosis, most commonly from vomiting or diuretics, or compensation for long-standing lung disease that retains carbon dioxide.

BUN

BUN rises when the kidneys filter less, when kidney blood flow falls (dehydration, heart failure), with high protein intake or breakdown, after bleeding into the upper gut, and with steroids. It falls with low protein intake, liver disease and pregnancy. In the UK and elsewhere, urea in mmol/L is reported instead; divide by 0.357 to get BUN in mg/dL, or use the BUN to urea converter.

Creatinine

Creatinine reflects both kidney filtration and muscle mass. It is used to calculate the eGFR, which most labs print alongside it. A creatinine within the "normal" range can still mean reduced kidney function in a small, older person, and a mildly raised creatinine can be normal in a muscular young man. See high creatinine for a full explanation and the GFR levels chart for staging.

Calcium

About half the calcium in the blood is bound to albumin. When albumin is low, total calcium reads low even if the active (ionised) calcium is normal, so calcium is often corrected for albumin – use the corrected calcium calculator. High calcium is most often due to primary hyperparathyroidism in outpatients, and to cancer in hospitalised patients. Low calcium can come from vitamin D deficiency, low magnesium, kidney disease or after neck surgery.

Values calculated from a BMP

The anion gap calculator, BUN/creatinine ratio calculator and serum osmolality calculator explain each of these in detail.

Worked example

A BMP shows sodium 140, chloride 104, bicarbonate 14 mEq/L. The anion gap is 140 − (104 + 14) = 22 mEq/L – raised. A low bicarbonate with a high anion gap is a "high anion gap metabolic acidosis", seen with ketoacidosis, lactic acidosis, kidney failure and some poisonings. If glucose on the same panel were 420 mg/dL, diabetic ketoacidosis would be high on the list – a medical emergency.

Common BMP patterns

Try the "Dehydration pattern" and "Diuretic pattern" examples in the explainer above to see how each value in these patterns is flagged.

Values that need prompt attention

Laboratories keep a list of critical values – results far enough from normal that the requesting clinician is contacted immediately. The exact thresholds vary by laboratory, but the explainer above flags values roughly in these zones as needing prompt medical attention:

These are not diagnostic cut-offs, and a value just inside them is not automatically safe. Symptoms, how quickly a value changed, and the person's usual baseline all matter.

The BMP in particular situations

Older adults

Older adults are more prone to low sodium (particularly with thiazide diuretics and some antidepressants), to dehydration with rising BUN, and to high potassium with kidney-protective blood-pressure medicines. Creatinine may look "normal" despite reduced kidney function because muscle mass declines with age, which is why eGFR – which includes age – is printed alongside.

People taking blood-pressure medicines

ACE inhibitors, angiotensin receptor blockers and mineralocorticoid antagonists can raise potassium and creatinine slightly. Diuretics can lower potassium, sodium and chloride and raise bicarbonate. A BMP is commonly checked a week or two after these medicines are started or changed for exactly this reason. A modest creatinine rise after starting such a medicine can be expected; your prescriber will judge whether the change is within the expected range.

Pregnancy

In normal pregnancy, BUN and creatinine fall because kidney filtration rises, and bicarbonate falls slightly because of mild over-breathing. A creatinine that would be normal outside pregnancy may be relatively high in pregnancy.

Athletes and heavy exercise

Intense exercise can temporarily raise creatinine and potassium, and muscular athletes have higher baseline creatinine. Endurance events with heavy water intake can lower sodium. If possible, avoid very strenuous exercise the day before a planned BMP.

Illness with vomiting or diarrhoea

Fluid losses change several values at once – often raising BUN, changing potassium and shifting bicarbonate up (vomiting) or down (diarrhoea). These usually return to normal after rehydration; persistent abnormalities are rechecked.

How to prepare for a BMP

• Fasting: often requested for 8–12 hours if glucose is to be interpreted as a fasting value. Water is usually allowed. Follow your clinician's instructions.
• Medicines: keep taking them unless told otherwise, but mention diuretics, blood-pressure tablets, potassium and supplements.
• Avoid a large meat meal the evening before if creatinine is the main concern, and avoid creatine supplements for a few days if possible.
• A difficult blood draw or delays in processing can raise potassium falsely.

When to see a doctor

Your clinician will review any flagged values. Seek urgent care if abnormal results come with:

• Confusion, seizures, severe weakness or palpitations.
• Fainting, chest pain or breathlessness.
• Very little urine output, or vomiting and inability to keep fluids down.
• Signs of very high blood sugar: extreme thirst, frequent urination, abdominal pain, rapid breathing.

Laboratories phone clinicians directly about "critical values" such as very high potassium or very low sodium.