If there's one topic that shows up everywhere in nursing school and on the NCLEX, it's lab values. They tell you what's happening inside your patient's body and which system is struggling. You need to know them for exams, and you'll use them every shift as a nurse.
Do Lab Values Differ Between Textbooks, HESI, and ATI?
Yes. Normal ranges vary slightly between textbooks, facilities, and resources like HESI and ATI. One resource might list normal calcium as 9 to 11 mg/dL, while another says 8.6 to 10.3 mg/dL.
Don't let that stress you out. On the NCLEX and nursing school exams, abnormal values are usually clearly abnormal. You won't be asked whether a calcium of 10.4 is high. You'll see something like a calcium of 13, which is out of range by any standard. Learn one set of ranges well, and focus on recognizing what's clearly abnormal.
Complete Blood Count (CBC) Normal Values
A CBC gives you the full picture of the cells in your patient's blood: white blood cells (WBCs) , red blood cells (RBCs), platelet (PLTS), hemoglobin, and hematocrit.
|
Lab |
Normal Range |
CBC Terms to Know
• Leukopenia is a low WBC count.
• Leukocytosis is a high WBC count.
• Thrombocytosis is a high platelet count.
• Thrombocytopenia is a low platelet count.
When you see a low platelet count, think bleeding.
Your patient doesn't have enough platelets to clot, so they're at serious risk for internal and external bleeding.
Memory Trick
Hemoglobin x 3 = Hematocrit
Memorize hemoglobin, then multiply by 3 to get hematocrit.
For a female, hemoglobin is 12 to 16. So 12 x 3 = 36 and 16 x 3 = 48, giving you a normal hematocrit of 36–48%.
Electrolyte Normal Values and Memory Tricks
Electrolytes appear everywhere in nursing school, so these are worth committing to memory early.
|
Electrolyte |
Normal Range |
Low |
High |
Electrolyte Memory Tricks
Potassium (3.5–5):
There are 3 to 5 bananas in every bunch, and you want them half ripe. That "half" reminds you of the .5.
Phosphorus (2.5–4.5):
Break the word apart. "Phos" sounds like four, and "us" is two (you and me). That gives you 2 to 4. Don't forget the .5!
Calcium (9–11):
My all-time favorite because it's so simple. Just call 9-1-1.
Magnesium (1.5–2.5):
Picture a magnifying glass that makes things look 1.5 to 2.5 times bigger.
Chloride (95–105):
Think of a chlorinated pool you want to jump into when it's super hot outside, like 95 to 105°F.
Coagulation Studies: aPTT, PT, and INR
Coagulation labs are especially important when your patient is on anticoagulants like heparin or warfarin. They measure how quickly the blood clots.
Heparin is monitored with aPTT (activated partial thromboplastin time).
Warfarin is monitored with PT/INR (prothrombin time/international normalized ratio).
|
Lab |
Not on Anticoagulant |
Therapeutic Range |
Memory Trick
"Too High, the Patient Will Die"
If PT/INR or aPTT is too high, your patient is at increased risk for bleeding. If it's too low, the anticoagulant isn't working and clots can form.
If the numbers are too high, the patient will die. If the numbers are too low, the clots will grow.
That's why we keep these values in the therapeutic range.
Want to go deeper? Check out my video on heparin vs. warfarin.
Lipid Panel Normal Values
A lipid panel measures the types of cholesterol in the blood and helps assess cardiovascular disease risk.
|
Lab |
Normal Range |
Memory Trick
HDL Is Your "Happy" Cholesterol
For the first three, you want low numbers. HDL is the exception.
HDL = Happy cholesterol, so you want it high.
LDL = Lousy (bad) cholesterol, so you want it low.
Hemoglobin A1C (HbA1c) Normal Range
HbA1c shows the average blood glucose over the last 2 to 3 months. That's because red blood cells live about 120 days. It's the best indicator of a patient's long-term diabetic control.
|
Result |
What It Means |
Arterial Blood Gas (ABG) Normal Values
An ABG measures pH and gases in the arterial blood. It's essential for interpreting acid-base imbalances.
|
Lab |
Normal Range |
Memory Trick:
Drop the 7
Take the pH range (7.35–7.45), drop the 7, and you have the CO2 range: 35–45.
Kidney Function Labs: BUN, Creatinine, and Urine Specific Gravity
|
Lab |
Normal Range |
What Elevated BUN and Creatinine Mean
When BUN and creatinine are both elevated, think kidney dysfunction. The kidneys can't filter out these waste products, so they build up in the blood. Of the two, creatinine is the better indicator of kidney function.
BUN and Creatinine Memory Tricks
BUN (7–20):
Think hamburger buns. A hamburger costs anywhere from $7 to $20.
Creatinine (0.6–1.2):
It's the same as lithium's therapeutic range. Lithium is excreted almost entirely by the kidneys, and creatinine tests how well the kidneys filter.
Urine Specific Gravity Memory Trick
A low specific gravity means the urine is diluted, so the patient likely has too much fluid. A high specific gravity means the urine is concentrated, so the patient is likely dehydrated.
Diluted makes the numbers go down. Concentrated makes the numbers go up.
Are you a visual learner?
Watch me break down all of these lab values, memory tricks included, in this quick video.
