Lab Values

Adult values. Labs differ a little, so trust the range printed on the patient's report. A critical value is one the lab phones to the provider right away.

Chemistry (BMP and friends)

SodiumNa

Normal

136–146mEq/L

Critical

< 120mEq/L> 160mEq/L

H: Too little water: dehydration, can't get to water (elderly, altered), diabetes insipidus.
L: Too much water for the salt: SIADH, heart or liver failure, diuretics, vomiting or diarrhea, beer drinkers.
!: Big or fast changes cause confusion and seizures. A chronic low sodium must come up slowly; correcting it too fast can cause permanent brain injury. Know the sending team's plan before running hypertonic saline or large fluid volumes.

PotassiumK

Normal

3.5–5.0mEq/L

Critical

< 2.8mEq/L> 6.2mEq/L

High K with a normal ECG? Ask whether the sample was hemolyzed. Treat ECG changes either way. On digoxin? Talk to medical control before giving calcium.

H: Kidney failure or missed dialysis, crush injury or rhabdo, acidosis and DKA, ACE inhibitors, ARBs, spironolactone. A hemolyzed sample reads falsely high.
L: Vomiting, diuretics, insulin, albuterol, alcohol use, low magnesium.
!: High: peaked T waves, then wide QRS, bradycardia, sine wave, arrest. ECG changes are the emergency, whatever the number. Treat per protocol (calcium, insulin with glucose, albuterol, bicarb). Low: weakness, PVCs, U waves, torsades. It won't stay up until magnesium is fixed.

ChlorideCl

Normal

95–105mEq/L

H: Large volumes of normal saline, diarrhea.
L: Vomiting, NG suction.
!: Mostly matters for the anion gap. Lots of normal saline can cause an acidosis on its own.

BicarbonateHCO₃ · CO₂

Normal

22–28mEq/L

Critical

< 10mEq/L> 50mEq/L

On a BMP this shows as "CO2" or "total CO2." It is bicarbonate, not the PaCO2 from a blood gas.

H: Vomiting, diuretics, or the kidneys making up for chronic CO2 retention (COPD).
L: Metabolic acidosis: DKA, shock and lactic acidosis, kidney failure, toxins, diarrhea.
!: A low bicarb means the patient is breathing hard to blow off CO2. If you sedate or intubate, keep their minute ventilation high or the pH will crash.

Blood urea nitrogenBUN

Normal

7–18mg/dL

H: Dehydration, kidney failure, upper GI bleed (digested blood), steroids.
L: Liver failure, malnutrition.
!: A BUN-to-creatinine ratio over 20 points toward dehydration or an upper GI bleed.

CreatinineCr

Normal

0.6–1.2mg/dL

H: Kidney injury or failure, rhabdo, dehydration.
!: A rise of 0.3 or more within 48 hours means kidney injury, even if the number is still "normal." Bad kidneys mean potassium trouble, fluid overload, and drugs that build up. Frail elderly patients with little muscle can have a "normal" creatinine and weak kidneys. On dialysis? Ask when the last run was and whether it was a full one.

GlucoseGlu

Normal

Fasting70–100mg/dL

Critical

< 50mg/dL> 450mg/dL

H: DKA, HHS, steroids, infection, stress.
L: Insulin or diabetes pills (sulfonylureas), sepsis, liver failure, alcohol, not eating.
!: Recheck with your own meter. Lows from diabetes pills can come back for a day or more. In DKA and HHS, insulin drives potassium down: know the K before insulin is started or turned up.

Calcium, totalCa

Normal

8.4–10.2mg/dL

Critical

< 6.0mg/dL> 13.0mg/dL

Low albumin makes total calcium read falsely low. Ionized calcium (on the blood gas) is the real number.

H: Cancer, overactive parathyroid, dehydration.
L: Massive transfusion (citrate in blood products binds it), kidney failure, pancreatitis, low magnesium.
!: Low: muscle cramps and tetany, long QT, low blood pressure that doesn't respond to fluids or pressors. High: confusion, weakness, dehydration, short QT.

MagnesiumMg

Normal

1.5–2.0mg/dL

Critical

< 1.0mg/dL> 4.7mg/dL

H: Kidney failure, a magnesium drip (pre-eclampsia).
L: Alcohol use, diarrhea, diuretics, acid-reflux pills (PPIs), malnutrition.
!: Low: torsades, and potassium and calcium won't stay up until it's fixed. On a magnesium drip for pre-eclampsia, levels above the critical value are often the goal. Judge by reflexes, breathing rate and urine output: reflexes disappear first, then breathing slows. Calcium is the antidote, per protocol.

PhosphorusPhos

Normal

3.0–4.5mg/dL

Called

< 1.0mg/dL

H: Kidney failure, rhabdo.
L: Refeeding after starvation, DKA treatment, alcohol use.
!: Very low phosphorus weakens the diaphragm and the heart. Watch for breathing failure.

Anion gapAG

Normal

Use the lab's range

Na − (Cl + HCO₃)

Acidosis with a normal gap usually means diarrhea or lots of normal saline.

H: Gap acidosis: something is adding acid. Think lactate (shock, sepsis), ketones (DKA, alcohol, starvation), kidney failure, toxins (methanol, ethylene glycol, aspirin, iron).
!: Low albumin hides a high gap: add about 2.5 for every 1 g/dL the albumin is below 4. Analyzers differ, so the normal range varies more than most.

Blood gas (venous first)

Most gases on transfers are venous (VBG). Venous numbers are listed first; arterial (ABG) is underneath for when one is drawn. Check the report header for which one you have.

Read a gas in four steps

pH Below normal is acidosis, above is alkalosis. Venous normal 7.32–7.42, arterial 7.35–7.45.
CO₂ Is it the lungs? High CO₂ with low pH is respiratory acidosis. Low CO₂ with high pH is respiratory alkalosis. Venous CO₂ runs a few points higher than arterial.
HCO₃ Is it metabolic? Low HCO₃ with low pH is metabolic acidosis. High HCO₃ with high pH is metabolic alkalosis.
Compensation CO₂ and HCO₃ move the same direction (both down or both up) to pull pH back toward normal. Compensation never overcorrects.

Metabolic acidosis: the arterial CO₂ the patient should have is about 1.5 × HCO₃ + 8 (± 2). On a venous gas, expect a few points above that. Well above: they aren't keeping up (tiring out or sedated). Well below: a second problem, a respiratory alkalosis on top.

Venous pH tracks arterial well. A normal venous CO₂ makes a high arterial CO₂ unlikely. In shock, neither venous CO₂ nor end-tidal CO₂ is reliable: trend both, and ask for an arterial gas before big vent changes. Venous pO₂ tells you nothing about oxygenation; use SpO₂.

pH

	Venous	Arterial
Normal	7.32–7.42	7.35–7.45
Critical	< 7.15> 7.59	< 7.20> 7.60

H: Alkalosis.
L: Acidosis.
!: Below about 7.20 the heart gets irritable and pressors work poorly.

Carbon dioxidepCO₂

mm Hg
	Venous	Arterial
Normal	41–51	33–45
Critical	< 19> 85	< 20> 70

H: Not breathing enough: COPD, opioids or sedation, fatigue, low vent rate.
L: Breathing too much: pain, anxiety, making up for a metabolic acidosis, overbagging.
!: CO₂ is the ventilation number. On a vent, rate and tidal volume move it. End-tidal CO₂ usually reads a little below the PaCO₂, and the gap widens with poor perfusion or bad lungs.

Bicarbonate on the gasHCO₃

Normal

Venous or arterial22–28mmol/L

The gas machine calculates this one. It should land close to the CO₂ on the BMP.

!: Low means metabolic acidosis, high means metabolic alkalosis. In a chronic CO₂ retainer (COPD), a high HCO₃ is usually the kidneys compensating. Ventilate them to their usual pH, not to a CO₂ of 40.

Base excessBE

Normal

About−2 to +2mEq/L

H: Positive: metabolic alkalosis, or the kidneys compensating for chronic CO₂ retention (COPD).
L: Negative (base deficit): metabolic acidosis. The more negative, the sicker, especially in shock and trauma.
!: Trend it with lactate to judge resuscitation.

LactateLac

Normal

Up to2mmol/LVenous lab range0.5–2.2mmol/L

Critical

> 5.0mmol/L

Venous lactate is what you will usually see. For sepsis, anything over 2 counts.

H: Shock or poor perfusion, sepsis, seizure, hard exertion, liver failure, metformin, epinephrine.
!: Over 2 with an infection: take sepsis seriously. Over 4 is higher risk still. A falling lactate usually means resuscitation is working. An epinephrine drip can raise lactate by itself.

Ionized calciumiCa

Normal

1.16–1.32mmol/LAbout4.6–5.3mg/dL

Critical

< 0.85mmol/L> 1.50mmol/L

If your report is in mg/dL, multiply mmol/L by 4: about < 3.4 or > 6.0 mg/dL

L: Massive transfusion, sepsis, pancreatitis, kidney failure.
!: Blood gas machines often report mmol/L, so check the units. Low ionized calcium makes bleeding and low blood pressure worse. In a bleeding patient, replace it long before it reaches the critical value.

Oxygen (arterial only)PaO₂

Normal

Arterial75–105mm Hg

Critical

< 40mm Hg

L: Hypoxemia: lung disease, shunt, not enough oxygen delivered.
!: Only an arterial pO₂ means anything. On a venous gas, ignore the pO₂ and use SpO₂.

Arterial O₂ saturationSaO₂

Critical

< 70%

!: Many gas machines calculate this from the PaO₂ instead of measuring it. That number is wrong in CO or methemoglobin poisoning; only co-oximetry measures it.

CarboxyhemoglobinCOHb

Critical

> 10%

H: Carbon monoxide: house fires, heaters, generators, running vehicles. Heavy smokers can run up near 10%.
!: A regular pulse ox reads normal in CO poisoning. Only a CO-oximeter or a co-ox blood gas shows it. The level falls on oxygen, so a low level hours later doesn't rule it out. Note when oxygen was started.

MethemoglobinMetHb

Critical

> 3.0%

H: Drugs and chemicals: benzocaine and other numbing sprays, dapsone, nitrites.
!: Chocolate-brown blood. At high levels the pulse ox settles in the mid-80s no matter how much oxygen you give, while the true saturation can be much lower. Go by the co-ox MetHb level and the patient, not the SpO₂.

Blood counts

White blood cellsWBC

Normal

4.5–11.0K/µL

Critical

< 1.0K/µL> 50.0K/µL

K/µL means thousands per microliter. Some reports write it × 10³/µL or × 10⁹/L; the number is the same.

H: Infection, inflammation, steroids, stress, leukemia.
L: Chemo, overwhelming sepsis, bone marrow problems.
!: Fever in a chemo patient is an emergency even if the WBC looks okay. The neutrophil count (ANC) is what matters; under 500 is severe. Mask, clean technique, antibiotics early.

HemoglobinHgb

Normal

Male13.5–17.5g/dLFemale12.0–16.0g/dL

Critical

≤ 6g/dL≥ 22g/dL

H: Dehydration, smoking, living at altitude, too many red cells.
L: Bleeding, chronic disease or kidney failure, red cells breaking down, dilution from IV fluids.
!: Hemoglobin lags behind fast bleeding. A normal first number does not rule out hemorrhage. Treat the patient and trend it.

HematocritHct

Normal

Male41–53%Female36–46%

Critical

≤ 18%≥ 55%

!: Roughly three times the hemoglobin. Same story as hemoglobin.

PlateletsPlt

Normal

150–400K/µL

Critical

≤ 10K/µL≥ 1,000K/µL

H: Inflammation, iron deficiency, after spleen removal, bone marrow disorders.
L: Bleeding and clotting using them up (DIC), liver disease, chemo, heparin (HIT), immune causes.
!: Under 10 they can bleed on their own, including into the brain. In active bleeding, platelets are given long before the critical value. On heparin with a big platelet drop, think HIT.

Clotting

Prothrombin timePT

Normal

11–15seconds

!: Read it as the INR. Same test, standardized so every lab matches.

INR

Range

Normalabout 1.0On warfarin, most patients2.0–3.0

Critical

≥ 4.0

H: Warfarin, liver failure, low vitamin K, DIC.
!: A head injury on any blood thinner is high risk. Apixaban (Eliquis), rivaroxaban (Xarelto) and dabigatran (Pradaxa) may barely move the INR, so a normal INR does not mean no blood thinner. Ask what they take and when the last dose was.

Partial thromboplastin timePTT

Normal

25–40seconds

H: Heparin, hemophilia, DIC, liver disease.
!: On a heparin drip a high PTT is expected. Many hospitals now adjust heparin by anti-Xa level instead. Ask which test, the target range, and who adjusts the drip during transport.

FibrinogenFib

Normal

213–415mg/dL

Critical

≤ 80mg/dL

Range varies a little with the lab's reagent.

L: DIC, massive bleeding, postpartum hemorrhage, after clot-busters (tPA, TNK).
!: Low fibrinogen in a bleeding patient needs cryo or fibrinogen concentrate; blood alone won't fix it. Bleeding patients get it long before the critical value.

Urine

Urine outputUOP

Normal

At least0.5mL/kg/hr

Example: a 70 kg patient should make at least 35 mL an hour.

L: Dehydration, shock, kidney injury, a kinked or blocked Foley.
!: Less than 0.5 mL/kg/hr for 6 hours meets the definition of kidney injury. Check the Foley before blaming the kidneys. Record output on every long transport.

Specific gravitySG

Normal

Under1.035

H: Concentrated urine: dehydration. Contrast dye and sugar push it up too.
L: Dilute urine: lots of fluid, diuretics, diabetes insipidus.

Urine pH

Normal

4.6–8.0

!: Rarely matters in transport. Some poisonings are treated by pushing urine pH up (aspirin), so you may see it ordered and trended.

BloodDipstick

Normal

Negative

H: Kidney stones, infection, trauma, bleeding problems. Blood on the dipstick with few or no red cells under the microscope points to myoglobin (rhabdo) or hemoglobin from red cells breaking down.
!: Tea- or cola-colored urine after a crush, long down time or seizures: think rhabdo and check CK and potassium.

Red and white cellsRBC · WBC (microscope)

Normal

RBC0–2/HPFWBC0–2/HPF

HPF = high-power field, what the tech counts under the microscope.

H: WBCs: infection or inflammation. RBCs: stones, infection, trauma, kidney disease.

Leukocyte esterase and nitriteLE · Nitrite

Normal

BothNegative

H: Urinary tract infection. Nitrite positive points to the gut bacteria that cause most UTIs. A UTI is a common source of sepsis in the elderly.
!: Altered elderly patient with a positive UA and soft blood pressure: urosepsis is possible, but a positive UA is common in the elderly and in anyone with a Foley without infection. Keep looking for other causes (stroke, GI bleed, another infection).

GlucoseUrine

Normal

Negative

H: Blood sugar high enough to spill into the urine, or an SGLT2 diabetes pill (empagliflozin/Jardiance, dapagliflozin/Farxiga, canagliflozin/Invokana), which makes urine sugar positive on purpose.
!: SGLT2 pills can cause DKA with a normal or only mildly high blood sugar. Sick, acidotic patient on one: think DKA even if the glucose looks okay.

KetonesUrine

Normal

Negative

H: DKA, alcohol, starvation, prolonged vomiting.
!: The urine dipstick misses the main ketone in DKA (beta-hydroxybutyrate), so it can underestimate how sick they are. A blood beta-hydroxybutyrate level is better. Urine ketones can even rise while DKA is getting better.

ProteinUrine

Normal

0–30mg/dL

H: Kidney disease, diabetes, high blood pressure. Pregnant over 20 weeks, or up to 6 weeks after delivery, with high blood pressure: think pre-eclampsia even if the protein is negative.

Pregnancy testUrine hCG

!: Positive means pregnant until proven otherwise. It changes drug choices and imaging. Belly pain or shock with a positive test: think ruptured ectopic. Very early pregnancy can still test negative.

Drug screenUrine UDS

!: A screen, not proof. Positive means recent use (days, or weeks for heavy marijuana use), not that they are impaired now. Standard opiate screens often miss fentanyl, oxycodone and other synthetics unless the lab tests for them separately. False positives happen. Treat the patient in front of you.

Heart, muscle, liver, pancreas

TroponinTrop

Normal

Troponin I, older tests≤ 0.04ng/mL

Units depend on the test. Older tests report ng/mL. High-sensitivity tests report ng/L, which is 1,000 times bigger (0.04 ng/mL = 40 ng/L). Use the cutoff printed on the report.

H: Heart muscle injury: MI, myocarditis, PE, sepsis, kidney failure, fast heart rates.
!: A rising or falling pattern matters more than one number. An early normal troponin does not rule out MI; the 12-lead comes first.

Creatine kinaseCK

Normal

Male25–90U/LFemale10–70U/L

H: Muscle breakdown (rhabdo): crush, long down time, seizures, stimulants, extreme exertion.
!: CK in the thousands means rhabdo. Watch potassium and kidneys, give fluids per orders, track urine output.

AST and ALTLiver enzymes

Normal

AST12–38U/LALT10–40U/L

H: Liver injury: hepatitis, alcohol, acetaminophen overdose, shock liver. AST also comes from muscle.
!: Values in the thousands point to acetaminophen overdose or a liver starved of blood flow.

Bilirubin, totalT bili

Normal

0.1–1.0mg/dL

H: Liver disease, blocked bile duct, red cells breaking down.
!: Shows as yellow eyes and skin once it climbs.

AlbuminAlb

Normal

3.5–5.5g/dL

L: Malnutrition, liver disease, losing it through the kidneys, critical illness.
!: Low albumin lets fluid leak into tissues (swelling) and makes total calcium read falsely low.

Lipase

Normal

13–60U/L

H: Pancreatitis (usually 3 times the upper limit or more), kidney failure.
!: Pancreatitis patients can third-space a lot of fluid and drop their calcium.

Toxicology and drug levels

These have no single "normal." The lab calls a critical value above these levels.

AcetaminophenAPAP · Tylenol

Critical

> 40µg/mL

!: The level is judged against hours since the overdose, so the time of ingestion matters. A level below the critical value can still need treatment. Early on they can look fine. NAC is the antidote.

SalicylateAspirin

Critical

> 40mg/dL

!: They breathe fast to blow off acid. If intubated, match their pre-intubation breathing or more; a normal vent rate can kill them. Check units: some labs report mg/L, which is 10 times the mg/dL number. Levels can keep climbing, so one level isn't enough.

DigoxinDig

Critical

> 2.0ng/mL

!: Nausea, vision changes, almost any arrhythmia. A high potassium in an acute overdose is a bad sign. A level drawn within 6 hours of a dose reads falsely high. Digoxin immune fab (DigiFab) is the antidote.

LithiumLi

Critical

> 1.4mEq/L

!: Tremor, confusion, seizures. Severe toxicity is treated with dialysis.

EthanolEtOH

Critical

> 300mg/dL

!: Protect the airway and check glucose. If the mental status is worse than the level explains, look for something else, such as a head injury.

Methanol and ethylene glycolToxic alcohols

Critical

> 10 · > 20mg/dL

Methanol > 10 · ethylene glycol > 20

!: Antifreeze, windshield washer fluid, moonshine. Early: high osmolar gap, normal anion gap. Late: the reverse. A normal result on either one does not rule them out.

OsmolalityOsm

Normal

275–295mOsm/kg

Osmolar gap = measured − (2 × Na + glucose ÷ 18 + BUN ÷ 2.8)

!: A big osmolar gap suggests a toxic alcohol. Drinking alcohol raises the gap too, so a drunk patient's gap has to be read with the ethanol level.