Formula Used
Urine ethanol to equivalent blood estimate: blood estimate = urine concentration / urine to blood factor.
Back extrapolated estimate: earlier estimate = collection estimate + elimination rate × hours since drinking.
Time to cutoff: time = (collection estimate - cutoff equivalent) / elimination rate, when collection estimate is higher.
Confidence interval: measured value ± z critical × measurement standard deviation.
Z score: z = (measured value - cutoff) / measurement standard deviation.
EtG decay model: time to cutoff = log2(measured value / cutoff) × selected half life.
Widmark comparison: BAC = grams alcohol / (body water ratio × body weight grams) × 100 - elimination during drinking.
How to Use This Calculator
Select the marker type first. Use urine ethanol for direct ethanol concentration. Use EtG when the report shows a metabolite value.
Enter the measured result and matching cutoff. Keep units consistent. Use mg/dL for ethanol and ng/mL for EtG.
Add timing, uncertainty, and elimination assumptions. Review the result table above the form after pressing the submit button.
Use the CSV button for spreadsheet records. Use the PDF button for a simple report copy.
Understanding Urine Alcohol Estimates
Urine alcohol testing can support a statistical review of recent alcohol exposure. The result is not the same as a breath or blood result. Urine holds fluid made over time, so timing matters. Hydration, bladder emptying, lab method, and collection delay can change interpretation. This calculator turns those inputs into transparent estimates.
Why the Inputs Matter
The measured concentration is the main laboratory value. A cutoff defines the comparison point. The urine to blood factor helps approximate an equivalent blood level when ethanol is measured. The elimination rate estimates how quickly alcohol may fall after drinking stops. Measurement uncertainty gives a confidence interval. These values make the result more useful than a single number.
Statistical Review
The tool computes a z score, an interval, and an estimated probability of being above the cutoff. These outputs do not prove impairment. They show how strongly the result sits above or below a chosen threshold. A small difference from the cutoff should be treated carefully, especially when uncertainty is high.
Practical Interpretation
Back extrapolation estimates an earlier level by adding expected elimination over time. This is sensitive to the entered hours and rate. The Widmark estimate uses drinks, weight, and body water ratio to create a separate comparison. Differences between both estimates can show whether the entered assumptions are realistic.
Safe Use
Use this calculator for education, planning, and data review. Do not use it as medical, legal, workplace, or forensic proof. Urine alcohol and metabolite tests need context. A qualified professional should review chain of custody, specimen validity, medication history, and laboratory reporting rules before any serious decision.
Reading the Output
Start with the displayed marker type and unit. Ethanol results use a urine to blood conversion. EtG results use a half life decay model. Next, review the cutoff comparison. Then read the confidence interval. A wide interval means less precision. The calculator also reports time above cutoff when the entered assumptions allow it. Export the CSV or report PDF when you need a record for notes, audits, or later review.
Always keep original lab reports. Enter values exactly as shown. Small unit mistakes can create large interpretation errors during any review and final record checks by reviewers.
FAQs
Is this calculator a legal alcohol test?
No. It is an educational estimator. Legal, workplace, or forensic decisions need validated lab procedures, chain of custody, specimen checks, and qualified review. Use this tool only to understand assumptions and calculations.
Which units should I enter?
Use mg/dL for urine ethanol. Use ng/mL for EtG. The calculator does not convert between these marker types because they represent different laboratory measurements and different interpretation models.
What is the urine to blood factor?
It is an assumption used to approximate blood alcohol from urine ethanol. The default is only a practical estimate. Real results can vary because urine represents pooled fluid over time.
What does the z score mean?
The z score compares the measured result with the selected cutoff using the entered standard deviation. A larger positive value means the result is farther above the cutoff under those assumptions.
Can EtG show impairment?
No. EtG is a metabolite marker. It can suggest prior exposure, but it is not a direct blood alcohol level and does not prove current impairment by itself.
Why is the confidence interval important?
It shows the possible spread around the measured result using your chosen uncertainty. A wide interval means the cutoff comparison should be read with more caution.
Why add standard drinks and body weight?
Those fields create a Widmark comparison estimate. It is separate from the urine result. The comparison helps show whether timing and concentration assumptions look consistent.
Can I download my calculation?
Yes. Submit the form first. Then use the CSV button for spreadsheet data or the PDF button for a simple saved report containing inputs, results, and summary.