Me-PFOSA-AcOH

What is Me-PFOSA-AcOH?

Me-PFOSA-AcOH, printed as MeFOSAA on many lab reports, is a PFAS compound measured in blood serum.

One molecule, several spellings. The CDC's NHANES data files call it Me-PFOSA-AcOH, short for 2-(N-methylperfluorooctanesulfonamido)acetic acid. Quest Diagnostics and NMS Labs print MeFOSAA on their PFAS panels, and the CDC's NHANES laboratory procedure manual uses MeFOSAA too. Research papers often write N-MeFOSAA. The registry number is CAS 2355-31-9, and LOINC, the code system many lab systems use to label results, files it as 2-N-Methyl-perfluorooctanesulfonamide acetate in serum or plasma, with Me-PFOSA-AcOH as the short name. If two reports you upload spell it differently, they're the same analyte. The ethyl version, Et-PFOSA-AcOH (EtFOSAA), is a different compound and a separate line on the report. Chemically, it's a sulfonamide with an eight-carbon fluorinated chain, and it sits upstream of PFOS. EPA's 2016 health effects document for PFOS says PFOS can form when N-methyl and N-ethyl perfluorooctane sulfonamides degrade, and that some of the PFOS measured in human serum likely comes from precursors that break down metabolically. The International Agency for Research on Cancer's 2025 monograph on PFOA and PFOS puts the sulfonamidoacetic acids in the same precursor group and says a substantial proportion of the PFOA and PFOS in the body may come from precursor intake. Neither source gives a conversion rate for MeFOSAA itself, so what they say applies to the family, not to this one compound. A Swedish serum study (Gebbink and colleagues, 2015, covering 1997 to 2012) found MeFOSAA among the highest-concentration PFOS precursors in samples from after 2000. Calafat and colleagues (2007) note that 3M ended production of PFOS and related sulfonyl fluoride-based chemistry in 2002, and that's the chemical family MeFOSAA comes from. That chemistry is also why it's the odd one out in the National Academies' guidance. In July 2022 the National Academies of Sciences, Engineering, and Medicine (NASEM) published clinical guidance that adds up seven PFAS in serum or plasma: MeFOSAA, PFHxS, PFOA, PFDA, PFUnDA, PFOS, and PFNA. The other six are perfluoroalkyl acids, the stable end of the chain; EPA's 2016 document notes PFOS isn't metabolized further. MeFOSAA is the only precursor in the sum. NASEM doesn't spell out why it chose these seven. It does say the committee limited its review to PFAS included in CDC's National Report on Human Exposure to Environmental Chemicals, and MeFOSAA is measured there. Labs build the total as a simple sum. Quest's PFAS 9 panel reports nine analytes because it splits PFOA and PFOS into linear and branched forms, and Maine's CDC calls the same arrangement a NASEM-9 sum. NASEM's bands at 2 and 20 ng/mL apply to the total, not to any single compound, and they're written for clinicians working with patients likely to have a history of elevated exposure. PFOS (Perfluorooctane Sulfonate) covers the framework in detail. Nobody has published a band for MeFOSAA alone, and this page doesn't offer one. CDC has measured it in surplus serum from 1999-2000 and in every NHANES cycle from 2003-2004 through 2021-2023. In 1999-2000 it was present at or above the detection limit in 1,420 of 1,456 samples, and Calafat and colleagues (2007) reported it in more than 90% of samples. In the 2021-2023 cycle it was at or above 0.10 ng/mL in 571 of 2,551 samples, a little over one in five, and the highest value was 3.8 ng/mL compared with 38.4 ng/mL in 1999-2000. The table below has every cycle. Read the percentages as rough. The detection limit moved between 0.09 and 0.52 ng/mL across cycles, the counts are raw sample counts rather than survey-weighted estimates, and the line isn't straight: detection was 39.3% in 2015-2016 and 59.0% in 2017-2018. The overall direction fits the end of PFOS-based production, but counts alone can't prove a cause.

Typical reference context

No clinical reference interval exists for Me-PFOSA-AcOH. What's published is a population distribution from the CDC's NHANES, shown below. It describes how often samples cleared the lab's detection limit in each survey, not what any value means for a person.

The counts are unweighted, and percentages are calculated from the CDC's published counts. Quest's PFAS 9 panel (July 2024) has a clinical reportable range of 0.10 to 25.00 ng/mL for each PFAS compound, so a value under 0.10 isn't quantified [14]. Me-PFOSA-AcOH isn't one of the PFAS named in EPA's April 2024 drinking-water rule (PFOA, PFOS, PFHxS, PFNA, HFPO-DA, and a Hazard Index), which EPA's page, updated May 18, 2026, describes proposals to change [20]. A blood value and a drinking-water limit are different things. PFOA (Perfluorooctanoic Acid) covers the rule's status.

What changed recently

The 2021-2023 NHANES cycle, which ran from August 2021 to August 2023, is the newest national data point: 571 of 2,551 samples at or above 0.10 ng/mL, with a highest value of 3.8 ng/mL. The CDC's 2025 summary of NHANES 1999 to March 2020 (Botelho and colleagues, January 2025) covers 17 PFAS but doesn't include this one, so the sources reviewed contain no recent published national trend analysis for it.

The sources reviewed contain no 2023 to 2026 study centered on this analyte alone.

For context on any single report, ATSDR's clinician page (reviewed July 7, 2026) says PFAS blood test results don't provide information for treatment or predict future health problems.

Tests often checked alongside this

The other six members of the NASEM sum usually come on the same panel: PFOS (Perfluorooctane Sulfonate), PFOA (Perfluorooctanoic Acid), PFHxS (Perfluorohexane Sulfonate), PFNA (Perfluorononanoic Acid), PFDA (Perfluorodecanoic Acid), and PFUnDA (Perfluoroundecanoic Acid). Larger research panels, such as NMS Labs' 19-analyte PFASure, add more compounds and print the NASEM total as a calculated line. The ethyl sibling Et-PFOSA-AcOH is measured in NHANES but isn't one of the seven.

Keeping reports comparable

Three details change from report to report: the name, the units, and the reporting limit. Quest and NHANES report in ng/mL, and ng/mL and µg/L are the same unit. Quest and NMS Labs both list a 0.10 ng/mL limit, while NHANES limits ranged from 0.09 to 0.52 ng/mL, so a "less than" value from one source isn't a number you can compare with a "less than" from another. Longetic organizes each value with the lab's own wording, units, and reporting limit, so two reports sit side by side exactly as printed.

What to ask your doctor

• Did my report list MeFOSAA separately, and which PFAS were added into the total on it?
• My MeFOSAA line says "less than" a number. What's this lab's reporting limit, and was my earlier report run at the same one?
• The NASEM bands were written for patients with a history of elevated exposure. Why was this test ordered for me, and how does it fit that framing?
• ATSDR says PFAS blood results don't provide information for treatment. How would you use this result in my care?

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