Can a Hair Follicle Test Go Back 12 Months? Understanding Detection Limits

How far back can a hair follicle drug test go?

A hair follicle drug test typically detects drug use within the last 90 days. This is because hair grows approximately 0.5 inches per month, and most tests analyze 1.5 inches of hair closest to the scalp. Testing beyond this length is uncommon and less reliable.

Longer hair samples can technically be tested to extend the detection window, but labs rarely process beyond 1.5 inches due to decreased accuracy and the potential for external contamination.

AMH Nationwide routes collections through five national lab networks: Quest Diagnostics, LabCorp, Omega Labs, United States Drug Testing Labs, and ExperTox. These labs standardly test up to 1.5 inches of hair to cover about three months of drug history.

How long do drugs stay in hair follicles?

Drugs enter the hair follicle from the bloodstream shortly after use and become trapped in the hair shaft as it grows. Because hair grows slowly, drugs remain detectable in hair for months.

The typical detection window for most hair drug tests is about 90 days. This period reflects the length of hair tested rather than the actual metabolic clearance of drugs from the body.

Hair testing does not detect very recent drug use within the past week because hair near the scalp takes time to grow out.

Can a hair follicle test go back 12 months?

Standard hair follicle drug tests cannot reliably detect drug use going back 12 months. The reason is that hair length and testing protocols limit detection to roughly 90 days.

While longer hair can be submitted for testing, labs generally do not analyze hair beyond 1.5 inches due to sample variability and external contamination risks.

If a longer detection window is needed, alternative testing methods or repeated testing over time might be considered.

How long does a hair follicle drug test take?

After collection at an AMH Nationwide authorized site, hair samples are sent to one of five national labs for analysis. The turnaround time usually ranges from 3 to 5 business days depending on the lab and test panel.

Every non-negative hair drug test is reviewed by a certified Medical Review Officer (MRO) as part of standard processing to ensure accuracy and reliability.

AMH Nationwide does not offer online orders; all testing requires contacting us at (877) 731-6362 to schedule and arrange lab orders.

Who typically orders hair follicle drug tests?

Employers, courts, probation officers, and individuals use hair follicle drug tests to detect drug use over a longer period than urine tests.

Hair testing is often preferred for non-DOT safety-sensitive roles because the Department of Transportation requires federally certified urine testing protocols for DOT-regulated positions.

AMH Nationwide provides lab orders and directs requesters to collection sites nationwide, working with major labs to ensure reliable results.

How does hair follicle testing compare to urine drug testing?

Hair follicle testing detects drug use over approximately 90 days, whereas urine testing typically detects recent use within 1 to 4 days depending on the drug.

Urine tests are federally certified for DOT safety-sensitive positions under 49 CFR Part 40, while hair tests are mainly used for non-DOT roles due to longer detection windows.

Hair testing is less invasive and harder to adulterate but cannot detect very recent drug use, unlike urine testing.

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