PFUnDA (Perfluoroundecanoic Acid)

What is PFUnDA (Perfluoroundecanoic Acid)?

PFUnDA is an 11-carbon PFAS that labs measure in blood serum, in ng/mL.

A PFUnDA line on a lab report often has no number on it. You see "<0.1", "<0.10 ng/mL", "ND", or "Not detected". These are different spellings of one statement: the instrument didn't register the compound at or above the lab's lowest reportable level. The cutoff goes by different names. CDC's NHANES documentation calls it the lower limit of detection and sets it at 0.10 ng/mL for PFUnDA. Quest's PFAS panel summary (July 2024) calls it a cutoff, also 0.10 ng/mL, with a reportable range of 0.10 to 25.00 ng/mL. NMS Labs lists a reporting limit of 0.1 ng/mL. Those three agree today, but nothing forces them to. A "<0.5" from one lab says the value fell below 0.5, and says nothing about whether it fell below 0.1. A non-detect isn't zero. The true concentration sits somewhere between zero and just under the cutoff, and the report doesn't say where. Researchers still need a number for their spreadsheets, so NHANES fills each below-limit result with the limit divided by the square root of 2. At 0.10 ng/mL that's about 0.07, and 0.07 is the smallest PFUnDA value in the 2017-2018 and 2021-2023 files. Nobody measured 0.07. It's a placeholder, and any table showing it is showing arithmetic. CDC's laboratory method says only that results below the limit are reported as less than the limit. The fill value is added later, in the public data files. How often does a "<0.10" show up? In the NHANES files, PFUnDA was at or above 0.10 ng/mL in 66.0% of 2017-2018 participants with a result (1,274 of 1,929), but in 25.7% of 2021-2023 participants (656 of 2,551). Two neighbors in the same 2017-2018 file were quantified far more often: PFDA in 1,711 of 1,929 and PFNA in 1,784. The cutoff stayed at 0.10 ng/mL across the four cycles in the table below, so the files don't explain the swings. These are counts of participants aged 12 and older, not survey-weighted estimates of the US population. CDC notes that special sample weights are required to analyze the data properly. A rarely quantified analyte can still sit in a guidance formula. In July 2022 the National Academies (NASEM) published clinical guidance that sums seven PFAS in serum or plasma: MeFOSAA, PFHxS, PFOA, PFDA, PFUnDA, PFOS, and PFNA, with linear and branched isomers of PFOA and PFOS counted. The committee's review was limited to PFAS in CDC's National Report on Human Exposure to Environmental Chemicals, and the chapter doesn't justify each analyte separately. The rule for non-detects is explicit: if any analyte is below the limit of detection, use the limit divided by the square root of 2 in the sum. That's the same fill NHANES uses. The consequence is easy to miss: the added amount is set by the lab's cutoff. At 0.10 ng/mL each non-detect adds 0.07 ng/mL. A lab with a higher cutoff adds more. Quest's panel summary describes exactly this, assigning 0.07 ng/mL to any analyte not detected at its 0.10 ng/mL cutoff. The framework itself, including the 2 and 20 ng/mL bands and who they're written for, is covered on PFOS (Perfluorooctane Sulfonate). Chemically, PFUnDA is a perfluorinated carboxylic acid with 11 carbons: ten fluorinated carbons plus the carboxyl carbon, one carbon longer than PFDA (Perfluorodecanoic Acid). No authoritative human half-life exists for it as of October 2026. ATSDR's 2021 toxicological profile lists half-lives for six PFAS and PFUnA isn't one of them. A 2024 systematic review of human half-lives pooled only PFOA, PFOS, and PFHxS, and noted that very little information exists for other compounds. Exposure routes are similarly thin. CDC's biomonitoring summary (reviewed April 2017) says sources of human exposure to this group are uncertain but probably include diet. This page doesn't list product categories, because the sources reviewed don't establish them for PFUnDA specifically.

Typical reference context

PFUnDA has no clinical reference interval. The table shows what published sources do provide: how often labs quantified it in a national survey, and the cutoffs labs print.

The percentages are unweighted counts, not national estimates. The NASEM bands apply to the sum of seven PFAS, not to PFUnDA alone, and they're guidance for clinicians caring for patients with a likely history of elevated exposure. A cutoff printed by a lab and a guidance band are different kinds of number.

What changed recently

The newest data point is CDC's NHANES file for August 2021 to August 2023, first published in August 2026. In it, PFUnDA was at or above 0.10 ng/mL in 25.7% of participants with a result, the lowest share among the four cycles in the table. Serum PFAS were measured in a one-half subsample of participants 12 and older.

On half-life, a systematic review by Rosato and colleagues (Environmental Research, online November 2023) found 13 studies and could pool estimates only for PFOA, PFOS, and PFHxS. PFUnDA remains without a pooled figure.

Research specific to PFUnDA is thin. Most papers report it as one analyte among many. Two 2024 examples show the pattern. A New York case-control study of pancreatic cancer (Long and colleagues, Exposure and Health) described PFUnDA as the least-detected PFAS in its panel, at about 70% of cases and controls, and reported an odds ratio of 2.60 (95% CI 1.11 to 6.09) for the highest versus lowest tertile. A study of rheumatoid arthritis in NHANES 2003-2018 adults (Qiao and colleagues, Environmental Health) reported 46.7% detection and found PFUnDA associations in opposite directions depending on sex and model. Both are observational, and neither shows that PFUnDA causes anything.

Tests often checked alongside this

Labs rarely run PFUnDA alone. It arrives as part of a PFAS panel: Quest's version lists nine analytes, counting PFOA and PFOS isomers separately, and NMS Labs lists 19. The other six members of the NASEM sum are PFHxS, PFOA, PFOS, PFNA, PFDA, and MeFOSAA. PFOS (Perfluorooctane Sulfonate) owns the guidance framework, and PFDA (Perfluorodecanoic Acid) is the next chain length down. Panels sometimes print a computed sum line beneath the individual results.

What can affect what your report shows

The lab's cutoff comes first. The same sample can print "<0.5" at one lab and a measured 0.2 at another. The specimen matters too: the lab methods reviewed here use serum, and some accept plasma. Quest asks for a red-top tube with no additives. As for exposure itself, the sources reviewed describe the routes as uncertain, and your doctor is the right person to discuss yours.

What to track over time

Treat each report as a snapshot from one lab on one date. Write down the lab's name, the collection date, the unit, and the printed cutoff, and note whether a value was measured or printed as "<". Without the cutoff, a "<0.5" in one year and a "<0.1" in another can't be compared. Longetic keeps uploaded reports organized and searchable, so the lab's original wording stays next to each value.

What to ask your doctor

• What cutoff did this lab use for PFUnDA, and does a "<0.10" differ from the "ND" on my last report?
• Does this panel print a sum, and if so, how did the lab handle the non-detects in it?
• Was the sample serum or plasma, and does that matter for comparing it with an earlier report from another lab?
• Which of these results does the guidance you use apply to, and what does it say for someone in my situation?

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