NCLEXNCLEX lab valuesApprox. 14 min·By Dr Irfan Mansuri
NCLEX Lab Values Cheat Sheet — study guide illustration
61 laboratory values grouped the way you will be asked about them, each with its normal range, the critical value that changes what you do next, and a line on what an abnormal result actually predicts.
How to use this page. This is exam-preparation material written to the NCLEX test plan, not clinical guidance. Answers and rationales are reproduced as written, and drug, lab and precaution details are included because the exam tests them — not as instructions for patient care. Always follow your nursing program, your facility policy and current manufacturer labelling for anything you do at the bedside, and check numbers against your own review text before you rely on them.
Memorising a range gets you to “abnormal”. The exam is asking what you do about it, so the column to spend time on is the note beside each value: which assessment it drives, which drug it makes unsafe, and which result you escalate rather than document.
Units matter. The same analyte appears in different units in different systems, and an item that gives you a number with a unit is often testing whether you noticed the unit at all.
Electrolytes
Test
Normal range
Units
Critical
What it tells you
Sodium (Na+)
135 – 145
mEq/L
< 120 or > 160
Follows water. Neuro signs dominate at both extremes; correct slowly to avoid cerebral injury.
Potassium (K+)
3.5 – 5.0
mEq/L
< 2.5 or > 6.5
Narrowest safe window of the common electrolytes. Never give IV push. Watch the ECG.
Chloride (Cl-)
98 – 106
mEq/L
< 80 or > 115
Moves with sodium; falls in vomiting and metabolic alkalosis.
Calcium (total)
9.0 – 10.5
mg/dL
< 7 or > 13
Low calcium = twitchy (Chvostek, Trousseau). High calcium = sluggish, stones, bone pain.
Ionised Calcium
4.5 – 5.6
mg/dL
< 3.2
The physiologically active fraction; unaffected by albumin.
Magnesium (Mg2+)
1.3 – 2.1
mEq/L
< 1.0 or > 4.0
Tracks calcium behaviour. High magnesium wipes out deep tendon reflexes first.
Phosphorus
3.0 – 4.5
mg/dL
< 1.0
Inverse to calcium. Rises in renal failure.
Bicarbonate (HCO3-)
22 – 26
mEq/L
< 15 or > 40
The metabolic arm of acid-base balance.
Renal
Test
Normal range
Units
Critical
What it tells you
BUN
10 – 20
mg/dL
> 100
Rises with dehydration, GI bleed and high protein load as well as kidney disease.
Creatinine
0.6 – 1.2
mg/dL
> 4.0
The more specific kidney marker. Doubling roughly halves GFR.
BUN : Creatinine ratio
10:1 – 20:1
> 20:1 suggests prerenal cause
A high ratio with normal creatinine points at hypovolaemia, not kidney damage.
eGFR
> 90
mL/min/1.73m2
< 15 (kidney failure)
Stages chronic kidney disease and drives renal dose adjustment.
Serum Osmolality
275 – 295
mOsm/kg
< 265 or > 320
Roughly 2 x Na + glucose/18 + BUN/2.8.
Urine Specific Gravity
1.005 – 1.030
fixed at 1.010
High = concentrated = dehydration or SIADH. Low = dilute = diabetes insipidus or overload.
Haematology
Test
Normal range
Units
Critical
What it tells you
Haemoglobin (male)
14 – 18
g/dL
< 7
Transfusion threshold is usually around 7 g/dL in a stable adult.
Haemoglobin (female)
12 – 16
g/dL
< 7
Assess for fatigue, pallor, tachycardia and orthostatic drop.
Haematocrit (male)
42 – 52
%
< 20
Roughly three times the haemoglobin.
Haematocrit (female)
37 – 47
%
< 20
Falsely high when the client is dehydrated.
WBC
5,000 – 10,000
/mm3
< 2,000 or > 30,000
Below 1,000 neutrophils means neutropenic precautions and no fresh flowers or raw produce.
Absolute Neutrophil Count
> 1,500
/mm3
< 500 (severe risk)
Fever in a neutropenic client is an emergency, even without other findings.
Interpreted alongside haemoglobin, haematocrit and the indices.
Coagulation
Test
Normal range
Units
Critical
What it tells you
PT
11 – 12.5
seconds
> 20
Extrinsic pathway. Follows warfarin.
INR
0.8 – 1.1 (2 – 3 on warfarin)
> 5
Mechanical valves often target 2.5 – 3.5. Antidote is vitamin K.
aPTT
30 – 40
seconds
> 70
Intrinsic pathway. Heparin therapeutic range is 1.5 – 2.5 times control. Antidote is protamine sulfate.
Fibrinogen
200 – 400
mg/dL
< 100
Consumed in disseminated intravascular coagulation.
D-dimer
< 0.5
mcg/mL
—
Sensitive but not specific; a normal result helps rule out clot.
Metabolic
Test
Normal range
Units
Critical
What it tells you
Fasting Glucose
70 – 100
mg/dL
< 50 or > 400
100 – 125 is prediabetes; 126 or above on two occasions is diabetes.
HbA1c
4 – 5.6 (target < 7 in diabetes)
%
> 10
Reflects roughly three months of glycaemic control.
Total Cholesterol
< 200
mg/dL
—
Interpret with the full lipid panel and risk profile.
LDL
< 100
mg/dL
—
The one to lower. Below 70 in very high risk clients.
HDL
> 40 (male), > 50 (female)
mg/dL
—
Higher is protective.
Triglycerides
< 150
mg/dL
> 500 (pancreatitis risk)
Requires a fasting sample.
Albumin
3.5 – 5.0
g/dL
< 1.5
Low albumin means oedema and falsely low total calcium.
Total Protein
6.0 – 8.0
g/dL
—
Low in malnutrition, liver disease and protein-losing states.
Total Bilirubin
0.3 – 1.0
mg/dL
> 15 in newborn
Jaundice becomes visible around 2 – 3 mg/dL.
Ammonia
15 – 45
mcg/dL
> 100
Rises in hepatic encephalopathy; lactulose lowers it.
ALT
10 – 40
units/L
—
More liver-specific than AST.
AST
10 – 40
units/L
—
Also found in cardiac and skeletal muscle.
Amylase
25 – 151
units/L
—
Rises early in acute pancreatitis.
Lipase
10 – 140
units/L
—
More specific for pancreatitis and stays elevated longer.
Uric Acid
2.7 – 8.5
mg/dL
—
Elevated in gout and tumour lysis syndrome.
Cardiac
Test
Normal range
Units
Critical
What it tells you
Troponin I
< 0.03
ng/mL
any elevation
The most specific marker of myocardial injury; rises within 3 – 4 hours.
CK-MB
0 – 3
ng/mL
—
Peaks around 18 hours; useful for detecting reinfarction.
BNP
< 100
pg/mL
> 900
Separates cardiac from pulmonary causes of dyspnoea; rises with volume overload.
Drug Levels
Test
Normal range
Units
Critical
What it tells you
Digoxin level
0.5 – 2.0
ng/mL
> 2.0
Toxicity shows as nausea, visual halos and bradycardia, and is worsened by low potassium.
Lithium level
0.6 – 1.2
mEq/L
> 1.5
Dehydration, low sodium and NSAIDs all push the level up.
Phenytoin level
10 – 20
mcg/mL
> 30
Toxicity causes nystagmus and ataxia. Gum overgrowth is a chronic effect.
Theophylline level
10 – 20
mcg/mL
> 20
Toxicity presents with tachycardia, tremor and seizures.
Vancomycin trough
10 – 20
mcg/mL
> 25
Draw immediately before the next dose; watch renal function and hearing.
Acetaminophen level
10 – 30
mcg/mL
> 200 at 4 hours
Antidote is acetylcysteine.
Arterial Blood Gas
Test
Normal range
Units
Critical
What it tells you
pH (arterial)
7.35 – 7.45
< 7.20 or > 7.60
Below 7.35 is acidosis, above 7.45 is alkalosis.
PaCO2
35 – 45
mmHg
> 60
The respiratory arm. Opposite direction to pH means a respiratory cause.
PaO2
80 – 100
mmHg
< 60
Below 60 correlates with a saturation under 90 percent.
SaO2
95 – 100
%
< 90
Target 88 – 92 percent in chronic CO2 retainers.
Base Excess
-2 to +2
mEq/L
—
Negative means metabolic acidosis, positive means metabolic alkalosis.
Maternal & Paediatric
Test
Normal range
Units
Critical
What it tells you
Newborn Glucose
40 – 60 (first day)
mg/dL
< 40
Jitteriness and poor feeding are early signs of hypoglycaemia.
Newborn Bilirubin (day 1)
< 6
mg/dL
> 15
Jaundice in the first 24 hours is always pathological.
Apgar Score
7 – 10 reassuring
0 – 3 needs resuscitation
Scored at 1 and 5 minutes on heart rate, respiratory effort, tone, reflex and colour.
Amniotic Fluid Index
5 – 25
cm
< 5 oligohydramnios
Low volume raises the risk of cord compression.
Magnesium (obstetric target)
4 – 7
mEq/L
> 8
Stop the infusion for absent reflexes, respirations under 12 or urine output under 30 mL/hour. Antidote is calcium gluconate.
Critical values in one list
These are the results that change the next ten minutes rather than the next shift. If a stem hands you one of these numbers, the answer is almost never “document and continue to monitor”.
Compiled and published by Dr Irfan Mansuri for irfanedu.com. Practice content is organised against the NCSBN test plan structure. Spotted something that looks wrong? Tell us and we will correct it.
