NCLEX-RN cheat sheet · Labs and diagnostics

Lab values: kidney, liver, heart, drug levels

Kidney and liver tests, cardiac markers, and drug levels

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The kidneys, liver and heart each leave their signature in the blood, and drug levels tell you whether a dose is helping or poisoning. The ranges here are general adult values: use your reference lab's ranges.

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At a glance

Kidney tests (general adult ranges)

Test	Normal	Worry when
BUN	6 to 20 mg/dL	High: kidney disease, dehydration, heart failure, gut bleeding, shock. Low (less common): liver failure, malnutrition, overhydration
Creatinine	Men about 0.7 to 1.3 mg/dL; women 0.5 to 0.95 mg/dL	Rising: the kidneys are failing; only the kidneys remove it. Muscle breakdown, dehydration and a blocked urinary tract raise it too, and some drugs affect the test
eGFR	About 90 to 120 mL/min/1.73 m², lower in older adults	Under 60 mL/min/1.73 m² for 3 months or more: chronic kidney disease. Under 15 mL/min/1.73 m²: kidney failure that needs immediate attention

What it changes: Many drugs are cleared by the kidneys, so a rising creatinine may mean a dose needs adjusting. Watch it closely with kidney-toxic drugs, like vancomycin and gentamicin, and report a rise.

Liver tests (general adult ranges)

Test	Normal	Meaning
ALT	About 4 to 36 U/L	Leaks out when liver cells are injured: hepatitis, cirrhosis, fatty liver, alcohol, acetaminophen
AST	About 8 to 33 U/L	Also comes from the heart and muscles: less specific to the liver
Total bilirubin	About 0.1 to 1.2 mg/dL	Around 2 mg/dL, the skin and eyes turn yellow: jaundice
Albumin	About 3.4 to 5.4 g/dL	Holds fluid in the vessels. Low in liver disease: ascites and swelling. Also falls with kidney disease, and when the body doesn't get or absorb enough protein

Liver and the INR: A liver panel includes the PT and INR. Liver disease itself can raise the INR, which raises the bleeding risk.

Ammonia and lactulose

The liver turns ammonia into urea, so a failing liver lets it build up.
Ammonia is toxic to the brain: confusion, low energy, even coma. That's hepatic encephalopathy.
Gut bleeding, kidney disease and low potassium can push it higher in liver disease.
Lactulose lowers it, working in the colon: the dose is adjusted to 2 or 3 soft stools a day. Count and record stools; report confusion that worsens.

Cardiac markers

Test	When and how	Watch for
Troponin	The test for heart muscle damage. Drawn for chest pain or worsening angina, then repeated on the schedule your institution and assay set	Even a slight rise often means damage. One normal value early on doesn't rule out a heart attack. Can stay high 1 to 2 weeks; also rises with fast rhythms, pulmonary embolism, heart failure, myocarditis
BNP	For heart failure signs: breathlessness, swollen legs or abdomen. Often run in the emergency department to tell a heart cause from a lung, kidney or liver cause	Under 100 pg/mL: acute heart failure less likely, not impossible, especially with obesity or preserved ejection fraction. Kidney failure, pulmonary embolism and sepsis raise it too

Serial troponins: High-sensitivity pathways retest at, for example, 0 and 1 hour, or 0 and 2; conventional assays differ. Report new or returning chest pain at once, even while you wait for the next result.

Drug levels

Drug	Level	Watch for
Digoxin	Heart failure: 0.5 to under 0.9 ng/mL, not the older 0.8 to 2	Toxicity can occur even in range: nausea, vision changes, rhythm problems. Apical pulse for a full minute before every dose. Low potassium makes it more toxic
Lithium	About 0.8 to 1.2 mEq/L for acute mania; drawn 12 hours after the last dose	Early toxicity: diarrhea, vomiting, drowsiness, weakness, poor coordination. Dehydration or a low salt intake raises it
Phenytoin	Total: 10 to 20 mcg/mL (free levels differ)	Above that, confusion appears, so a level is checked at the first sign of toxicity
Gentamicin	Trough under 2 mcg/mL	Protects the kidneys and hearing

Peaks and troughs: A peak is drawn when the drug is at its highest; a trough just before the next dose, at its lowest. Time the dose around the draw, and if a trough isn't back yet, check before you give the next dose.

Reading kidney and liver tests

The eGFR is checked regularly in people at risk: diabetes, high blood pressure, heart disease, or kidney disease in the family.
Creatinine varies with size and muscle mass, one reason the eGFR also accounts for age and sex.
Some drugs, like famotidine and trimethoprim, can affect the creatinine test: share the medication list.
Ammonia: alcohol, diuretics, opioids and valproic acid can affect the test, and the client shouldn't smoke before the draw.
Most newborns have some jaundice; whether a level is too high depends on how fast it's rising, the baby's age, and prematurity.

Check yourself

Most specific kidney marker? Creatinine: BUN also rises with dehydration, GI bleeding and protein intake.
eGFR 48 mL/min/1.73 m² for the past 4 months? Chronic kidney disease.
First troponin normal, 1 hour after chest pain began? Expect repeat troponins, not discharge.
Cirrhosis, confused, high ammonia? Expect lactulose, adjusted to 2 or 3 soft stools a day.

Priority and safety calls

★ New or returning chest pain: report it at once, even while you wait for the next troponin.
★ A drug level comes back high: assess for the toxic signs, and report it before the next dose is due.
A trough drawn after the dose isn't a trough and can't guide dosing: report the timing problem, and arrange a correctly timed trough just before the next dose.
Skipping or doubling a dose isn't the nurse's call.
Digoxin with nausea, halos and a level of 2.6 ng/mL: report the level and symptoms before giving the next dose.
With vancomycin, report ringing in the ears, hearing loss or a rising creatinine.
Read levels with the chemistry: low potassium makes digoxin more toxic; dehydration or a low salt intake raises lithium.

How the NCLEX tests it

Compare with normal, act, and use the urgency ladder.
Classic stems: a rising creatinine on a kidney-toxic drug, confusion with a high ammonia, repeated troponins, a toxic digoxin or lithium level.
Traps: a trough drawn after the dose, one normal troponin, and a dose given before a pending level.
Creatinine and eGFR track the kidneys; watch them with kidney-toxic and kidney-cleared drugs.
Liver disease can raise both the INR and the ammonia; high ammonia means confusion, and lactulose.
Troponin is repeated; BNP points to heart failure. Troughs come just before the dose.

Practice it next

This sheet comes from Lab values II: kidney, liver, heart and drug levels in our NCLEX-RN course. Try free practice questions, or see the lessons it was written from.

Free NCLEX practice questions The NCLEX-RN course

Quick self-quiz

An eGFR under ___ mL/min/1.73 m² for 3 months or more means chronic kidney disease.
Show answer
60
A total bilirubin around ___ mg/dL turns the skin and eyes yellow.
Show answer
2
Lactulose is adjusted to 2 or 3 soft ___ a day.
Show answer
stools
A trough is drawn just ___ the next dose.
Show answer
before
In heart failure, digoxin now targets 0.5 to under ___ ng/mL.
Show answer
0.9
A lithium level is drawn ___ hours after the last dose.
Show answer
12
A BNP under ___ pg/mL makes acute heart failure less likely, not impossible.
Show answer
100

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