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Blood Test Tracker

Vancomycin (Trough)

The lowest vancomycin level in your blood, drawn right before your next dose, used to check this IV antibiotic is working without building up.

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What it is

Vancomycin is an antibiotic given by IV for serious infections, including MRSA. A trough level is the amount left in your blood just before the next dose, when it is lowest. Your care team reads it with your kidney function to adjust dosing. Newer guidelines often use a calculated number called the AUC (a measure of total exposure over 24 hours) instead of the trough alone, but many labs and hospitals still report trough levels.

Why it matters

Vancomycin needs enough exposure to treat the infection, and too much can harm the kidneys. Kidney function can change quickly in someone who is sick, which changes how fast vancomycin leaves the body. A trough is a simple way to see whether the drug is building up or clearing too fast, and it helps your team adjust the dose.

If it’s low

A low trough means less vancomycin is left before the next dose. That can be expected with some dosing plans, and your team may judge the dose by AUC instead. It can also mean the dose is smaller than your body needs, so teams look at it together with the infection being treated.

Common causes

  • Fast kidney clearance, which can happen in younger or critically ill people
  • Missed or delayed doses
  • A sample drawn long after the previous dose
  • A larger volume of body fluid, for example after large IV fluid volumes

What can help

  • Ask your team how they decide the target for your infection
  • Ask whether the dose should be checked by an AUC calculation

If it’s high

A high trough means vancomycin is leaving the body more slowly than planned, or the dose is large for your body. Falling kidney function is the most common reason. Higher exposure is linked to a greater chance of kidney injury, so your team will usually check your creatinine and may change the dose or the time between doses.

Common causes

  • Reduced kidney function or dehydration
  • A recent dose increase
  • A sample drawn too early, or from the IV line the drug runs through
  • Other medicines that can strain the kidneys, such as aminoglycoside antibiotics or amphotericin B
  • Older age, which often lowers kidney clearance

What can help

  • Ask your care team how your kidney function is being tracked
  • Make sure the blood draw was timed right before your dose and not taken from the infusion line
  • Tell your team about every medicine you take

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

For adults: 10–20 µg/mL. Source: Quest Diagnostics, American Journal of Health-System Pharmacy, Journal of the Association of Medical Microbiology and Infectious Disease Canada. Labs treat above 25 µg/mL as urgent.

What can affect your result

  • Time between the last dose and the blood draw
  • Kidney function, hydration, age and body weight
  • Whether the sample came from the infusion line
  • Other medicines that affect the kidneys
  • Dosing method: trough-only or AUC-guided (often with Bayesian dosing software)
  • A sample drawn after the next dose has started, or well before it is due, does not give a true trough.
  • Drawing blood from the same IV line used for the infusion can falsely raise the result.
  • Changing kidney function changes levels quickly, so a trough can be out of date within a day or two.
  • Quest rejects serum separator (gel) tubes for this test; it asks for a red-top tube without gel (plasma in EDTA or heparin tubes is also accepted).

Just before the next dose (ARUP asks for collection about 30 minutes before the dose). Timing matters more than time of day. The half-life is 4 to 6 hours with normal kidney function (FDA labeling), so levels settle within about a day or two of a dose change, but much more slowly when the kidneys are not working well.

When to talk to a clinician

Tell your care team promptly about much less urine, new swelling, ringing in the ears or hearing changes, or a new rash while you are on vancomycin. Many hospitals ask the care team to call about troughs above 25 µg/mL. Call 911 or your local emergency number for trouble breathing, swelling of the face or throat, or fainting during or after an infusion.

Questions you could ask

  • Are you using an AUC calculation to dose my vancomycin?
  • How often will my levels and kidney tests be checked?
  • How long do I need to stay on this antibiotic?
  • Was this sample drawn at the right time, and not from the infusion line?
  • Should the dose or the time between doses change based on my kidney function?
  • Should we check my kidney tests again soon?

Questions people ask

Why doesn't my doctor aim for a trough of 15–20 like I read online?

That target came from guidance in 2009. In 2020, a revised guideline from ASHP, IDSA, PIDS and SIDP dropped the 15–20 trough target for serious MRSA infections and recommended dosing by a calculated AUC instead, in part because high trough targets were linked to more kidney injury. Your care team may still use the trough, or an AUC estimate that uses your trough.

What is AUC, and can I see mine on my lab report?

AUC stands for area under the curve, a measure of how much vancomycin your body is exposed to over 24 hours. It is calculated by dosing software or a pharmacist from one or two levels and your dose times, so it does not usually appear as a lab result. Ask your care team if they calculate it.

How do I convert mg/L or µg/mL to µmol/L?

Multiply mg/L (the same as µg/mL) by 0.69. So 15 mg/L is about 10.4 µmol/L. To go the other way, multiply µmol/L by 1.449.

Show the science and sources

Units

  • 1 µg/mL = 1 µg/mL
  • 1 µg/mL = 1 mg/L
  • 1 µg/mL = 0.69 µmol/L

Open the Vancomycin trough unit converter

For clinicians and researchers

Vancomycin is a glycopeptide eliminated almost entirely by glomerular filtration (half-life 4 to 6 hours with normal renal function, about 7.5 days in anephric patients) and is about 55% protein bound; it is not metabolized (FDA labeling). The 2009 consensus guideline recommended troughs of 15–20 mg/L as a surrogate for an AUC to MIC ratio above 400. The 2020 ASHP/IDSA/PIDS/SIDP revision instead recommends an AUC of 400–600 mg·h/L for serious MRSA infections (assuming a MIC of 1 mg/L), retracts the 15–20 mg/L trough target, and endorses Bayesian software that estimates AUC from one or two levels. Because many labs and clinicians still use trough-guided dosing, the Quest interval of 10.0–20.0 mg/L remains widely printed. Immunoassay results differ slightly between platforms (ARUP uses a KIMS method). Hospital critical limits for the trough vary widely (median 25, range 12–80 µg/mL). mg/L and µg/mL are the same unit.

LOINC 4092-3 (primary), 39797-6. Specimen: serum-or-plasma.

Sources

  1. Vancomycin, Trough (test code 8579), Quest Diagnostics
  2. Therapeutic monitoring of vancomycin for serious methicillin-resistant Staphylococcus aureus infections: A revised consensus guideline and review by the ASHP, IDSA, PIDS and SIDP, American Journal of Health-System Pharmacy (2020)
  3. A Canadian perspective on the revised 2020 ASHP-IDSA-PIDS-SIDP guidelines for vancomycin AUC-based therapeutic drug monitoring for serious MRSA infections, Journal of the Association of Medical Microbiology and Infectious Disease Canada (2021)
  4. Vancomycin hydrochloride for injection prescribing information, DailyMed, National Library of Medicine
  5. Drug Critical Limits for Urgent Physician Notification, Clinical Pharmacology & Therapeutics (Kuang, Ibrahim, Cheng, Kost) (2026)
  6. Vancomycin (PubChem compound 14969), 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.

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