Acetaminophen (Paracetamol)
Measures how much acetaminophen (Tylenol) is in your blood, mainly to check for an overdose.
AI-verified against cited sources. Awaiting expert reviewAlso called APAPLOINC 3298-7
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What it is
Acetaminophen, also called paracetamol or Tylenol, is a common pain and fever medicine. It is also in many cold, flu and sleep products, so it is easy to take more than you realize. This blood test shows how much of the drug is in your blood at the moment of the draw. After a possible overdose, the result is read together with the number of hours since the dose, because the same number means different things at different times.
Why it matters
Too much acetaminophen can badly damage the liver, sometimes before symptoms show up. A level paired with the time of the dose helps a care team decide whether treatment is needed. If you took a normal dose, this test is usually not needed, and a single level does not tell you whether your daily intake is safe.
If it’s low
A low or undetectable level means little acetaminophen was in the blood when the sample was drawn. The drug clears within hours, so a late sample can be low even after a large dose. A low level does not rule out liver injury.
Common causes
- No recent acetaminophen
- A sample drawn many hours after the last dose
- A normal dose that has already cleared
What can help
- After a possible overdose, ask about liver tests (AST, ALT and INR) even if the acetaminophen level is low
If it’s high
A high level means a lot of acetaminophen is in the blood. Whether it is a concern depends on how many hours have passed since the dose and whether it was taken all at once or over several days. A number without the timing cannot be judged.
Common causes
- A sample drawn within a few hours of a normal dose, when levels are briefly at their highest
- Taking too much at once, on purpose or by accident
- Taking several products that each contain acetaminophen
- Taking more than the label dose over several days
What can help
- If you think you or a child took too much, call Poison Control (1-800-222-1222 in the US) or emergency services right away, even if you feel fine
- Check the labels of cold, flu, allergy and sleep products for acetaminophen, APAP or paracetamol
- Ask your clinician about the safest daily limit for you, especially if you drink alcohol regularly or have liver disease
What can affect your result
- Time since the dose: a level before 4 hours after an overdose may not show the peak
- Single or repeated doses: the standard treatment chart is only for one acute ingestion at a known time
- Extended-release products, which can delay and flatten the peak
- Units: mcg/mL and mg/L are the same number, and µmol/L is about 6.6 times larger
- A sample drawn less than 4 hours after an acute overdose may not show the peak and can be falsely reassuring (acetylcysteine prescribing information).
- The standard treatment line applies to a single immediate-release ingestion at a known time. It does not apply to extended-release products, doses spread over hours or days, or an unknown time of ingestion.
After a suspected overdose the sample is timed from the hour of ingestion, not the time of day. Levels fall quickly after a normal dose: the adult half-life is about 2.4 hours (acetaminophen injection prescribing information). In an overdose, clearance can be slower.
When to talk to a clinician
If you think you or a child took more than the label dose, call Poison Control (1-800-222-1222 in the US) or go to an emergency department right away, even if you feel fine. Early symptoms can be mild or missing while the liver is at risk. Nausea, vomiting, belly pain, or yellow skin or eyes are reasons to be seen urgently.
Questions you could ask
- What is the safest daily amount of acetaminophen for me given my health and medicines?
- How many hours after the dose was this sample drawn, and does the lab's chart apply to this situation?
- Which liver tests should we check, and when should we repeat the level?
- Since the sample was drawn some time after the dose, do I still need follow-up liver tests?
Questions people ask
Why does the time since the dose matter so much?
Acetaminophen levels rise after a dose and then fall over several hours. The treatment line on the Rumack-Matthew chart starts at 150 mcg/mL at 4 hours and drops to 37.5 mcg/mL at 12 hours. So the same number can sit below the line early on and above it later.
Can this test tell me if my regular daily dose is safe?
No. A level after a normal dose only shows what is in your blood at that moment. The safe daily amount differs from person to person, and the product label lists a daily limit. Ask your clinician or pharmacist what is right for you, especially if you drink alcohol regularly or have liver disease, and ask about liver tests if you are worried.
How do I convert mcg/mL to µmol/L?
Multiply mcg/mL (which equals mg/L) by 6.62. For example, 150 mcg/mL is about 990 µmol/L.
Show the science and sources
Units
- 1 mcg/mL = 1 mcg/mL
- 1 mcg/mL = 1 mg/L
- 1 mcg/mL = 6.616 µmol/L
Open the Acetaminophen unit converter
For clinicians and researchers
Acetaminophen is mostly cleared by glucuronidation and sulfation. A small fraction is oxidized to the reactive metabolite NAPQI, which glutathione normally neutralizes. In overdose, glutathione runs low and NAPQI injures liver cells. The Rumack-Matthew nomogram plots the level against hours after a single acute ingestion. Its lower treatment line is 150 mcg/mL at 4 hours and 37.5 mcg/mL at 12 hours, and levels above 300 mcg/mL at 4 hours were associated with liver damage in about 90% of patients (acetaminophen injection prescribing information). It is meant for levels drawn 4 hours or more after one immediate-release ingestion at a known time. Earlier levels may not represent the peak (acetylcysteine prescribing information). The nomogram is not validated for repeated supratherapeutic ingestion, extended-release products or unknown time of ingestion, and current US and Canadian consensus guidance covers those cases separately. After 1,000 mg IV in adults, the mean peak is about 28 mcg/mL (wide variation between people) with a half-life of about 2.4 hours. Conversion: 1 mcg/mL = 1 mg/L = 6.62 µmol/L.
LOINC 3298-7 (primary), 14581-3. Specimen: serum-or-plasma.
Sources
- Acetaminophen Injection prescribing information (Overdosage and Clinical Pharmacology sections), U.S. FDA label via NLM DailyMed (Baxter Healthcare) (2024)
- Acetylcysteine Injection prescribing information (assessment after acute acetaminophen ingestion), U.S. FDA label via NLM DailyMed (Sagent Pharmaceuticals) (2022)
- Acetaminophen Level, MedlinePlus, National Library of Medicine
- Management of Acetaminophen Poisoning in the US and Canada: A Consensus Statement, JAMA Network Open (2023)
- Acetaminophen (PubChem CID 1983), PubChem, National Library of Medicine
AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.