NCLEX-RN cheat sheet · Labs and diagnostics
Lab values: blood counts, clotting, chemistry
Normal ranges, what changes your care, and how urgent it is
AI-checkedChecked by AI against current guidelines, with spot-checks by a registered nurse.
A lab result is only a number until you ask what it means for this client, and what you'll do about it. These are general adult values: ranges differ by lab and by population, so use your own lab's range.
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At a glance
Blood count (general adult ranges)
| Test | Normal | Watch for |
|---|---|---|
| White cells | 4,500 to 11,000 cells/mcL | Low: infection risk (chemotherapy, radiation, marrow failure, autoimmune disease, some viruses and drugs). High: most often bacterial infection; also inflammation, burns, pregnancy, the stress of surgery |
| Hemoglobin | Men about 13 to 18 g/dL; women 12 to 16 g/dL | Low: anemia, from bleeding, a failing marrow or red cells breaking down: fatigue, a fast pulse, breathlessness. High: often dehydration; also long-term low oxygen, smoking |
| Hematocrit | Men about 40 to 55%; women 36 to 48% | High: dehydration |
| Platelets | 150,000 to 400,000 cells/mcL | Under 150,000: thrombocytopenia. Under 50,000 cells/mcL: bleeding risk rises. Over 400,000: can raise the risk of clots |
Read it with fluid status: A hemoglobin that rises after fluid loss may simply mean the blood is concentrated.
What the blood count changes
- Neutrophils fight infection, so the differential matters most. A very severe infection can push the count down: a low number doesn't rule infection out.
- After chemotherapy, a low count plus a fever of 100.4 °F (38 Celsius) or higher is an emergency, even if the client feels fine.
- Low platelets: follow your facility's bleeding precautions; report new bruising or bleeding right away.
- On heparin, falling platelets can mean HIT: report it, because heparin may need to stop. Usually days 5 to 10, earlier after recent heparin; judge the relative fall, not an exact day.
- In most stable adults, consider red cells below a hemoglobin of 7 g/dL, individualized to the client.
Clotting tests
| Test | Normal | On a blood thinner |
|---|---|---|
| PT | 11 to 13.5 seconds | Longer on warfarin |
| INR | About 0.8 to 1.1 | Warfarin: usually 2 to 3; the target depends on why it's prescribed |
| aPTT | About 25 to 35 seconds | Heparin infusion: aPTT or anti-Xa, per protocol |
Warfarin: INR above 3: bleeding risk; below 2: clot risk. A high INR means notify the prescriber before the next dose.
Chemistry (general adult ranges)
| Test | Normal | Low | High |
|---|---|---|---|
| Fasting glucose (at least 8 hours) | 70 to 99 mg/dL | Under 70 mg/dL: hypoglycemia: shakiness, sweating, a fast heartbeat, confusion; under 54 mg/dL is level 2 | 100 to 125 mg/dL: prediabetes. 126 mg/dL or more: diabetes, if confirmed |
| A1C (3-month average) | Under 5.7% | — | 5.7 to 6.4%: prediabetes. 6.5% or more: diabetes, if confirmed. Goal for many with diabetes: under 7% |
| Sodium | 135 to 145 mEq/L | Brain cells swell: confusion, headache, vomiting, cramps, seizures. From diuretics, vomiting, heart failure, SSRIs | Usually water loss: sweating, diarrhea, burns, or a client who can't drink enough |
| Potassium | About 3.5 to 5 mEq/L | Weakness, cramps, palpitations, dangerous rhythms; digoxin toxicity more likely. From diuretics, vomiting, diarrhea, laxative overuse, low magnesium | Often no symptoms; palpitations, a slow, weak or irregular pulse; can stop the heart. From kidney failure, ACE inhibitors, spironolactone, tissue damage |
| Calcium | Total about 8.5 to 10.2 mg/dL; ionized calcium has its own, lower range | — | — |
Glucose and A1C: Diabetes needs a second abnormal test, unless hyperglycemia is unequivocal. A random glucose of 200 mg/dL or more often means diabetes. A normal glucose this morning doesn't cancel a high A1C.
How urgent is it? (example values: your facility sets its own)
| Rung | Example | What you do |
|---|---|---|
| Expected | WBC 12,000 cells/mcL the day after surgery | Document it; keep watching the trend |
| Watch | A1C 7.4% in known diabetes | Report it routinely, and teach |
| Act now | INR 4.6 on warfarin; very low platelets | Report it now; protect the client |
| Emergency | Potassium 6.4 mEq/L with an irregular pulse; glucose 40 mg/dL with confusion | Treat what you can, call rapid response, and stay with the client |
The drug moves it up: Symptoms, trends and the client's medicines move a result up the ladder. A potassium of 3.3 mEq/L is a watch item on its own, but act-now before digoxin or a diuretic.
Reading a result
- Ask: is it new, is it getting worse, and what does it mean for this client and their medicines?
- Compare with the last results: a slow trend tells a different story from a sudden change.
- Check the timing: a fasting and a random glucose are read against different numbers.
Warfarin and heparin checks
- The INR drifts with a wrong dose, alcohol, new antibiotics, supplements and diet: ask what changed.
- Teach: keep vitamin K foods steady; avoid alcohol, cranberry and grapefruit; report nosebleeds, bleeding gums, dark urine or black stools.
- Before a heparin drip: baseline aPTT, INR and platelets. Then the aPTT is checked often; the protocol sets the range and adjusts the rate.
Priority and safety calls
- ★ A critical result changes your priorities: report it to the provider promptly, before routine tasks.
- ★ Glucose under 70 mg/dL: treat the low before you give anything else. Check glucose before insulin.
- INR above 3 on warfarin, even without bleeding: notify the prescriber before giving the dose.
- Digoxin due and the potassium is low: report the potassium before giving the digoxin.
- New confusion on a diuretic: check the sodium.
- Potassium of 6.4 mEq/L with a slow, irregular pulse: the heart is already affected, so report it first.
How the NCLEX tests it
- Compare results with normal, and act on them.
- Classic stems: a high INR, low platelets, a low white count with fever, potassium before a diuretic or digoxin, sodium with new confusion.
- Report first? Compare the dangers, not just how far each number is from normal.
- Warfarin follows the INR; heparin follows the aPTT or anti-Xa.
- Sodium affects the brain, and potassium the heart.
- Traps: treating every abnormal value as urgent, missing the one that is, and forgetting the drug the value affects.
Practice it next
This sheet comes from Lab values I: blood counts, clotting and chemistry in our NCLEX-RN course. Try free practice questions, or see the lessons it was written from.
Quick self-quiz
- Normal platelets: 150,000 to ___ cells/mcL.
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400,000 - On warfarin, the INR target is usually 2 to ___.
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3 - Normal sodium: 135 to ___ mEq/L.
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145 - Hypoglycemia is a glucose under ___ mg/dL.
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70 - After chemotherapy, a low white count with a fever of ___ °F (38 Celsius) or higher is an emergency.
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100.4 - An A1C of ___% or more points to diabetes, if confirmed.
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6.5 - A heparin infusion is guided by the aPTT or an ___ level, per protocol.
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anti-Xa
Sources
- MedlinePlus, CBC blood test
- MedlinePlus, Prothrombin time (PT)
- MedlinePlus, Partial thromboplastin time (PTT)
- MedlinePlus, Basic metabolic panel
- MedlinePlus, Hemoglobin A1C test
- CDC, Preventing Infections in Cancer Patients: Neutropenia and Risk for Infection
- Open RN, Nursing Pharmacology 2e, 6.12 Blood Coagulation Modifiers
- American Society of Hematology, Heparin-induced thrombocytopenia guidelines
More labs and diagnostics cheat sheets
- Lab values: kidney, liver, heart, drug levels NCLEX cheat sheet
- Vital signs and deterioration NCLEX cheat sheet
Educational use only. This sheet is a study aid for the NCLEX-RN, not a substitute for clinical judgment, your facility’s policy or the provider’s orders. Where practice varies, follow facility policy and state law. NCLEX® and NCLEX-RN® are registered trademarks of NCSBN, which does not endorse these materials.