PFHpA (Perfluoroheptanoic Acid)

What is PFHpA (Perfluoroheptanoic Acid)?

PFHpA is a seven-carbon PFAS that labs can report in blood serum.

PFHpA has a seven-carbon chain, one fewer than PFOA, and it shows up on some lab reports in serum next to other PFAS. What makes it unusual is how little national guidance names it. It's missing from the EPA's 2024 drinking-water rule, and it's missing from the National Academies' 2022 framework for PFAS blood testing. A handful of states wrote it into their own water limits anyway. A PFHpA line on a report sits in the gap between those rulebooks, and that gap is the most useful thing to understand about it. Don't assume it lingers for years. Published half-lives for PFHpA are short next to its better-known relatives, and they differ by study. In a 2020 study in Environmental Health Perspectives, researchers followed airport employees whose drinking water had been contaminated by firefighting foam; 17 of 26 were tracked monthly for five months after the exposure ended. They estimated a PFHpA half-life of 62 days (95% CI 51 to 80 days). In the same study, PFOA came out at 1.77 years and PFHxS at 2.87 years. A half-life is the time it takes a blood level to fall by half once intake stops. The ATSDR toxicological profile lists a much longer figure from a 2013 study by Zhang and colleagues: 1.2 years in 66 people over 50, and 1.5 years in 20 women aged 50 or younger. Different people and different designs produced those numbers. The fair summary is a range from about two months to about a year and a half, and neither end is a number for any one person. The state picture is a patchwork. Massachusetts limits the sum of six PFAS, known as PFAS6, to 20 ng/L: PFOS, PFOA, PFHxS, PFNA, PFHpA, and PFDA. MassDEP published that standard on October 2, 2020. Rhode Island's Department of Health lists the same six compounds under a 20 ppt limit effective September 18, 2024. Vermont's 2019 rule capped the sum of five PFAS, PFHpA among them, at 20 ppt, and the state says an updated Water Supply Rule took effect on January 1, 2026; check the state's current rule text for the compounds it lists now. Maine has an interim 20 ppt standard for six PFAS. Connecticut went the other way: in June 2022 it replaced a summed action level with four single-compound action levels (PFOS, PFNA, PFOA, PFHxS), and PFHpA isn't one of them. Outside the US, Directive (EU) 2020/2184 includes PFHpA in the list of 20 PFAS behind its "Sum of PFAS" parameter, applicable from January 12, 2026. Federal and clinical guidance skip it. As of October 2026, EPA's PFAS drinking-water page says the 2024 rule covers PFOA, PFOS, PFHxS, PFNA, HFPO-DA, and a mixture index, and that PFHpA isn't covered; the PFOA (Perfluorooctanoic Acid) page tracks that rule and its current status. The NASEM clinical framework sums seven other PFAS and leaves PFHpA out; the PFOS (Perfluorooctane Sulfonate) page explains the framework. What does that mean for a lab result? A water limit and a blood result are different measurements. Water limits are written in ng/L and serum results are typically reported in ng/mL, a thousandfold difference in the unit alone, and no published water limit converts into a blood threshold. For blood, none of the bodies above publishes a band for PFHpA, so a PFHpA value has no published yardstick to sit beside. Panels differ, too. Quest's PFAS 9 panel summary (July 2024) doesn't list PFHpA, while NASEM noted in 2022 that a commercial panel from NMS Labs did. Whether your report shows the marker depends on which panel the lab ran. CDC measured serum PFHpA in six NHANES cycles, from 2003-2004 through 2013-2014, and dropped it from the 2015-2016 and 2017-2018 files. In those six cycles, between 7.6% and 20.5% of results fell at or above the lab's detection limit. That's a population distribution, not a health threshold, and the detection limit itself changed partway through, so the cycles don't line up cleanly.

Typical reference context

No clinical reference interval exists for PFHpA in blood. The first table shows what CDC's NHANES files report about how often it's detected. The second shows who has published water limits that name it, and who hasn't.

NHANES serum PFHpA, share of results at or above the detection limit (percentages calculated from the counts in each CDC data file):

Published limits and guidance, and whether PFHpA is named:

These numbers describe water limits and how often a lab detected the compound across the US population. They don't say what any one person's result means.

What changed recently

Most of the change is regulatory, and none of it adds PFHpA to a national rule. Rhode Island's six-PFAS limit took effect on September 18, 2024. Vermont's updated Water Supply Rule took effect on January 1, 2026, and the EU's PFAS parameters became applicable on January 12, 2026. On May 18, 2026, EPA proposed two changes to its 2024 rule: an option for water systems to request until 2031 to comply, and a rescission of the limits for PFHxS, PFNA, HFPO-DA, and the mixture index. PFHpA was never part of that rule, so neither proposal touches it. MassDEP's page says it has until April 26, 2028 to finalize new state rules after a March 2026 primacy extension, and that it will propose amendments at least as stringent as EPA's limits. The page doesn't say whether PFAS6 stays in its current form.

Research specific to PFHpA is mostly laboratory and animal work. Recent titles include a 26-week subchronic toxicity study of PFHpA in rats (Environment International, February 2026), a zebrafish developmental and mitochondrial toxicity study (January 2023), and a mouse study of prenatal PFHpA exposure and spermatogenesis in offspring (July 2023). A 2025 paper in Communications Medicine proposes a translational framework linking PFHpA to fatty liver disease in adolescents. These are research findings in animals and cells or proposed frameworks; they don't give a threshold or a meaning for a person's blood value. Human studies that include PFHpA often analyze it as one of many PFAS at once, which makes results hard to pin on a single compound.

Tests often checked alongside this

On a lab report, PFHpA usually sits in a PFAS panel with other compounds, and which ones appear depends on the lab. The nearest neighbors are the compounds that share its state limits: PFOS (Perfluorooctane Sulfonate), PFOA (Perfluorooctanoic Acid), PFHxS (Perfluorohexane Sulfonate), PFNA (Perfluorononanoic Acid), and PFDA (Perfluorodecanoic Acid). For another shorter-chain compound with a different history, see PFBS (Perfluorobutane Sulfonate).

What to track over time

A PFHpA result is only comparable to an earlier one if the lab, method, reporting limit, and unit match. Keep the collection date, lab name, unit, and printed reporting limit next to each value. CDC's own detection limit moved from 0.3 and 0.4 ng/mL to 0.1 ng/mL across cycles, and two labs can differ the same way. If a later report drops PFHpA, the panel changed; that isn't a result. Longetic keeps those details attached to each uploaded report, so you can see your own values over time as each lab printed them.

What to ask your doctor

• My report lists PFHpA, but the NASEM sum of seven doesn't include it. How, if at all, does a PFHpA value factor into your thinking?
• Which lab and method produced this result, and what's its reporting limit? Will the next test use the same panel?
• Should I bring my water utility's PFAS report to the appointment, and what would you want to see in it?
• Is there anything about my history that makes a PFAS result more or less relevant to you?

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