Reading an LTI Wipe Test Report — A Walkthrough for QA, Inspectors, and Operators

When a state nuclear-medicine inspector reviews your wipe-test binder, they’re looking for three things: was the survey run on time, was the equipment properly calibrated, and were any failures actually addressed. Every printed wipe test report from an LTI counter is structured to answer those three questions on a single page. Here’s how to read one.

Real Multi-Wiper Wipe Test Report — date stamped, isotope, background, MDA, trigger, net activity, units, PASS/FAIL per location — The actual printed report from a Multi-Wiper running a daily wipe set. Real data. We’ll walk through every column.

The header — date, time, set, count time, MDA formula

Every report starts with a header that establishes when the survey was run and how it was configured:

Date / time stamp — "WIPE TEST REPORT — 7/15/09 15:34:03 (COUNT TUBE)" tells you exactly when this survey ran. Inspectors look here first to confirm the survey was performed on schedule (typically weekly, sometimes more frequently for high-volume hot labs).
Wipe set name — "WIPE SET: DAILY" identifies which stored wipe set was run. Survey routes are stored on the instrument with names ("DAILY", "WEEKLY", "HOT BENCH", "PET SUITE", etc.) so the operator just selects from the library.
Count time — "COUNT TIME: 1.0 MIN" documents the per-tube counting interval. Longer count times produce lower MDAs; this number ties directly into the math below.
MDA formula — "MDA = ((2.71/Ts) + (3.29)(SQRT(Rb/Tb + Rb/Ts)))/Eff" — this is the Currie-derived equation for Minimum Detectable Activity that the instrument used to compute the MDA values in the table. Printing the formula on every report establishes the math on the page rather than hiding it in a manual.

The location block — one per wipe

Each wipe location gets its own block on the report. The block includes:

LOCATION: — the name of the wipe location. Because wipe locations are programmed into the instrument with descriptive names (e.g., BENCH1, TOILET, CAMERA1, DKNOB1, CHAIR, TREADMILL, THYROID PROBE, SINK), you don’t need to decipher handwritten labels or remember which tube went where.
ISOTOPE — the isotope being tested for at that location. On the Multi-Wiper, the isotope is pre-specified per location (so the trigger and efficiency are correct). On the Wiper Gold, you can specify the isotope OR run a "FULL" spectrum to identify unknown isotopes from the MCA. Either way, the report shows what was tested for.

Then for each tested isotope, the report prints a row with:

The five columns that matter: BKGND (the location-specific background count rate — measures detector cleanliness and shielding)
MDA (the calculated minimum detectable activity for this measurement, from the Currie formula above)
TRIGGER (the regulatory or institutional threshold above which the wipe fails — set per location)
NET ACTIVITY (gross count minus background, in the chosen units)
UNITS (CPM by default, or DPM when an isotope with stored efficiency is selected — AutoSpect™ handles the conversion automatically)
RESULT (PASS or FAIL — the instrument compares NET ACTIVITY against TRIGGER and prints the result in plain language)

How to read a single line

Take a real line from the sample report:

LOCATION: BENCH1 — FULL — BKGND 105 — MDA 39.6 — TRIGGER 2000 — NET ACTIVITY 4315 — UNITS CPM — RESULT FAIL

Translated to English: "At BENCH1, the wipe was tested over the full energy spectrum. The background count rate at this location was 105 cpm. The instrument’s minimum detectable activity for this measurement was 39.6 cpm. The institutional trigger for this location is 2000 cpm. The wipe’s net activity (after subtracting background) was 4315 cpm. Because 4315 exceeds the 2000 trigger, the result is FAIL."

That’s a real failure on a hot bench — the wipe found contamination above the threshold the institution set. The report flags it with bold "FAIL" so the operator can’t miss it.

What an inspector wants to see in your binder

Three things, in order:

1. The survey was run on time and consistently.

Inspectors want a stack of dated reports on a regular cadence (typically weekly for routine hot labs, daily for high-volume operations). The date/time stamp in the header is what they check. Gaps in the date sequence are the single biggest red flag — they suggest the survey wasn’t actually performed, or wasn’t logged.

2. The equipment was properly configured.

The header line tells the inspector that the count time is reasonable (a 1-second count time would be a problem; a 1-minute count time is appropriate). The MDA formula on the report shows the math the instrument used. The TRIGGER values on each row show that institutional thresholds are programmed correctly (a hot bench with a 2000 cpm trigger is reasonable; a 2,000,000 cpm trigger would be wrong).

3. Failures were addressed.

If a wipe FAILS, the inspector wants to see follow-up documentation: a re-survey after decontamination showing PASS, an incident report describing the cleanup, and ideally a corrective-action note in the binder. The fact that the LTI report flags failures in bold is a feature, not a bug — failures should be visible, not buried in a column of numbers.

The fix here is simple: when a wipe fails, decontaminate the location (we recommend S4FE-D® for radio-iodine and most clinical isotopes), then re-survey. The re-survey report shows PASS at the same location, dated after the cleanup. Two reports stapled together demonstrate the corrective action loop, which is exactly what regulators expect.

Reading the report on the Wiper Gold (single-detector)

The same column structure applies on the Wiper Gold, with two additions worth knowing:

Unknown-isotope identification. If a location is configured to test on the FULL spectrum (rather than a pre-specified isotope), the Wiper Gold’s MCA can identify the contaminating isotope from the spectrum itself and print the result. This is useful for forensic surveys after an unexpected contamination event.
Decay-corrected results. The Wiper Gold can report results decay-corrected to a reference time (e.g., dose preparation time) using its built-in Decay Calculator. The report header notes when decay correction is active so an inspector knows to check the reference timestamp.

Common questions from QA staff

"What does AutoSpect™ do to the report?"

AutoSpect™ is the instrument’s spectrum-compensation engine. When an isotope with stored efficiency is selected, AutoSpect converts the raw count rate to true DPM and reports activity in DPM (rather than just CPM). The "UNITS" column on the report shows when DPM is being reported — that’s AutoSpect at work.

"Can I customize the report layout?"

The default layout is what most state inspectors and QA programs expect. The instrument supports report customization to a limited degree (which fields print, summary at top vs. bottom, etc.) but we recommend keeping the standard layout because it’s what auditors are used to reading.

"What if my printer dies?"

The report can also be exported via the configurable serial / USB port to a connected PC, where it can be saved as a digital file or piped into a LIMS. A failed printer doesn’t mean a failed survey.

Reading an LTI wipe test report.