Which lab values should make a nurse act right away?
NCLEX-RN topic: Laboratory values
- Use the range printed on the client's own lab report.
- Potassium outside 3.5–5.1 mEq/L threatens heart rhythm.
- Sodium shifts show up in the brain: confusion, seizures, coma.
- Glucose under 70 mg/dL, alert client: 15–20 g fast-acting carbohydrate, recheck in 15 minutes.
- Usual warfarin INR target is 2.0–3.0; heparin is followed with PTT.
Key facts
- Reference ranges differ slightly between labs, so the nurse uses the range printed on the client's own lab report.
- Potassium (3.5–5.1 mEq/L in Open RN) controls heart rhythm; both hyperkalemia and hypokalemia can cause dangerous dysrhythmias.
- Potassium is never given by IV push because it can stop the heart.
Show all 7 key factsShow fewer
- A blood glucose below 70 mg/dL is low; an alert client who can swallow gets 15–20 g of fast-acting carbohydrate and a recheck in 15 minutes.
- Without warfarin, a normal INR is 0.8–1.1; on warfarin the usual target is 2.0–3.0, and an INR above 3.0 raises bleeding risk.
- PTT, not PT/INR, is the test used to keep a heparin dose safe and effective.
- Platelets below 150,000/mcL is thrombocytopenia; below 50,000/mcL bleeding risk is higher even with everyday activity.
Quick check1 question · 2 more at the end
The nurse reviews morning laboratory results for four clients. Which result requires the nurse's immediate follow-up?
Correct answer: C.
Potassium governs the heart's electrical activity, so hyperkalemia can cause dysrhythmias and cardiac arrest. Among several abnormal results, the one that threatens circulation most is the priority. Mild sodium and calcium deviations matter but are not immediately life-threatening in an otherwise stable client.
A A sodium only slightly below range is a concern to report, but it is far less immediately dangerous than a potassium that can stop the heart.
B A calcium just above range can cause nausea or constipation over time; it is not the most urgent result here.
C Correct: a potassium of 6.2 mEq/L is well above range and can cause life-threatening dysrhythmias, so it needs immediate follow-up.
D An INR of 1.0 is within the normal range for a client who is not taking warfarin.
Full lesson
Each part starts with its main idea. Open a part when you want the details.
The short answer: Compare every result with the lab's own range, then look at the client. Potassium outside 3.5–5.1 mEq/L threatens heart rhythm, sodium shifts affect the brain, glucose below 70 mg/dL needs treatment now, and a high INR or a platelet count under 50,000/mcL raises bleeding risk. Report dangerous values to the provider promptly.
1 Why do some lab results need action right now?Electrolytes, glucose and clotting tests have narrow normal ranges, and a small shift can upset the heart, the brain or blood clotting. 1 min
Electrolytes, glucose and clotting tests have narrow normal ranges, and a small shift can upset the heart, the brain or blood clotting. Your job is to compare each result with the range on the client's own lab report, look at the client, and report anything dangerous. Labs use slightly different ranges, so the numbers below are the ones our sources give.
| Test | Range used here | What goes wrong |
|---|---|---|
| Sodium | 136–145 mEq/L | Brain: headache, confusion, seizures |
| Potassium | 3.5–5.1 mEq/L | Heart: dysrhythmias, cardiac arrest |
| Calcium | 8.6–10.2 mg/dL | Nerves and muscles: tingling, spasms |
| Fasting glucose | 70–99 mg/dL (below 70 is low) | Brain: shakiness, confusion, seizures |
| INR | 0.8–1.1 (2.0–3.0 on warfarin) | Bleeding or clotting |
| Platelets | 150,000–400,000/mcL | Bleeding |
2 Why is potassium the electrolyte nurses watch most closely?Potassium keeps the heart's electrical activity steady, so a level that is too high or too low can trigger a dangerous rhythm. 1 min
Potassium keeps the heart's electrical activity steady, so a level that is too high or too low can trigger a dangerous rhythm. Hyperkalemia can come from kidney failure, potassium-sparing diuretics or potassium supplements. Signs include weakness, nausea, palpitations, a slow or irregular pulse and ECG changes.
Emergency treatment may include IV calcium to protect the heart and IV insulin with glucose to move potassium into the cells. When insulin is used this way, blood glucose is checked closely.
Hypokalemia can follow vomiting, diarrhea or loop and thiazide diuretics. Look for weakness, dysrhythmias, lethargy and a thready pulse. Potassium replacement is given by mouth or diluted in IV fluid, never by IV push.
3 How do sodium and calcium problems show up?Sodium changes show up mostly in the brain, because water moves into or out of brain cells. 1 min
Sodium changes show up mostly in the brain, because water moves into or out of brain cells. Hyponatremia often follows too much water or too many hypotonic IV fluids and causes headache, confusion, seizures and coma. Hypernatremia usually follows water loss and causes intense thirst, sticky mucous membranes, irritability and confusion.
Calcium affects nerves and muscles. Hypocalcemia causes numbness and tingling of the lips and fingers, cramps and tetany. Look for a positive Chvostek sign (facial twitch when the facial nerve is tapped) and a positive Trousseau sign (hand spasm under an inflated BP cuff). Hypercalcemia causes nausea, vomiting, constipation, thirst and muscle weakness.
4 What glucose level should make you act?A blood glucose below 70 mg/dL is low and needs treatment now. 1 min
A blood glucose below 70 mg/dL is low and needs treatment now. Early signs include shaking, sweating, hunger, a fast heartbeat and irritability. Below 54 mg/dL, unclear thinking and seizures become more likely.
If the client is alert and can swallow, give 15–20 g of fast-acting carbohydrate, recheck in 15 minutes, and repeat until the level is back in range. Glucagon is used for severe lows.
5 How do you read clotting results?Clotting tests tell you whether the client is likely to bleed or to clot. 1 min
Clotting tests tell you whether the client is likely to bleed or to clot. PT/INR monitors warfarin. Without warfarin the INR is about 0.8–1.1; on warfarin the target is usually 2.0–3.0.
Above an INR of 3.0 the bleeding risk rises, and below 2.0 the clot risk rises.
PTT monitors heparin and helps the provider keep the dose safe and effective. A platelet count under 150,000/mcL is thrombocytopenia; under 50,000/mcL, even daily activities can cause bleeding. Watch for signs of bleeding such as nosebleeds or easy bruising.
6 What the nurse doesThe nurse checks the client as well as the number, then acts on the most dangerous result first. 1 min
The nurse checks the client as well as the number, then acts on the most dangerous result first.
- Assess: compare the result with the range and with earlier results, then check the client (symptoms, pulse, ECG, signs of bleeding).
- Act on the priority: treat a low glucose per protocol right away, and report dangerous values such as high potassium or a high INR to the provider promptly.
- Teach: clients on warfarin need regular INR checks, and clients on loop or thiazide diuretics may need potassium.
Common mistakes
The traps students fall into most. Read these before you practice.
Watch out: Sodium problems show up mainly as brain changes (confusion, seizures), not as heart rhythm changes.
Watch out: On warfarin, an INR of 2.5 is on target, not a reason to hold the drug; the normal 0.8–1.1 range applies only to clients not taking it.
Watch out: Warfarin is monitored with PT/INR, not PTT; heparin is the drug followed with PTT.
Watch out: Treat a low glucose in an alert client first and recheck in 15 minutes, not wait an hour to see if it rises.
Watch out: Low calcium causes tingling and muscle spasms (Chvostek and Trousseau signs), not constipation; constipation and thirst point to high calcium.
How to remember it
Tie each lab to the organ it threatens and the values become much easier to recall.
Memory hook: "K keeps the Kardiac rhythm, Na steers the brain, and when Ca is low the muscles go" (twitching and spasms).
Self-check:
- Name the electrolyte that can stop the heart if pushed IV.
- State what INR range is on target for a client taking warfarin.
- Describe the two steps for a glucose of 62 mg/dL in an alert client.