Perfluorotridecanoic acid (PFTrDA)

Some of the synthetic chemicals used to make products stain-resistant, waterproof, and greaseproof stay in your body for years and slowly accumulate. This test measures one of them, giving you a window into your personal exposure to a chemical family that most standard blood work never looks at.

This is a newer, research-stage measurement rather than an established clinical test. There are no agreed 'normal' cutoffs yet, so a single number should be treated as a starting point for tracking, not as a diagnosis.

What This Chemical Actually Is

PFTrDA (perfluorotridecanoic acid) belongs to a large group of industrial compounds known as PFAS, sometimes called 'forever chemicals' because their strong carbon-fluorine bonds resist breaking down. Your body does not make this molecule. Its presence reflects outside exposure that has built up over time.

It is a 'long-chain' member of the family, and longer-chain versions tend to stick around in the body and the environment more than shorter ones. A result here signals how much of this specific chemical you have absorbed, not any normal biological process working harder or slower.

One important point before the health findings: almost all of the human research on this chemical measured it in blood (serum or plasma), not urine. In fact, in large population testing, long-chain PFAS like this one were rarely detectable in urine at all, while only shorter-chain versions showed up there with any regularity. Where studies are cited below, they reflect blood-based measurements unless stated otherwise, so any read on urine is indirect.

Preterm Birth

The clearest human signal comes from pregnancy. In a study of 1,990 mother-infant pairs across China, this chemical showed the strongest link to preterm birth of any PFAS measured.

Babies whose umbilical cord blood was higher in this compound had about 51% higher odds of preterm birth for each step up in exposure (measured in cord serum, not urine), with raised risk seen for both moderate and late preterm birth. Researchers also traced the association to disruptions in bile-acid and fat-handling pathways, which adds biological plausibility rather than a purely statistical link.

If you are pregnant or planning to conceive, this is the association most worth knowing about, and it is a strong reason to focus on lowering ongoing exposure well before conception.

Endometriosis and Reproductive Health

A Spanish study of 42 women with surgically confirmed endometriosis and 90 without found that higher blood levels of this chemical were linked to roughly 74% higher odds of the condition for each doubling of the plasma concentration.

This finding is suggestive, not settled. The study was small, the overall PFAS mixture was only weakly associated with endometriosis, and a larger Chinese study that looked specifically at this compound did not reproduce the link. Broader reviews conclude PFAS as a group are associated with reproductive problems, but stop short of proving cause and effect.

Cholesterol and Blood Pressure

Across several blood-based studies, higher levels of this chemical track with less favorable heart-health markers. A cross-sectional study of 575 adults in Jinan, China found that a PFAS mixture including this compound was linked to higher total cholesterol and LDL (the 'bad' cholesterol), and this compound was among those with comparatively larger effects on blood fats.

A long-running Norwegian study with repeated samples from 1986 to 2016 reached a similar conclusion: higher serum levels of this chemical were positively associated with total cholesterol and LDL over decades, while triglycerides showed no link. In a separate Chinese mixture analysis of a different population, this compound was a leading contributor to higher odds of high cholesterol, elevated LDL, and high blood pressure.

These are exposure associations measured in blood, not proof that lowering this one chemical will move your cholesterol. But they are a practical reason to pair this test with a standard lipid panel rather than reading it in isolation.

When the Findings Point the Other Way

Some studies report the opposite of what you might expect. One Chinese case-control study found higher levels of this chemical associated with lower breast cancer odds, another linked it to lower odds of the autoimmune condition Sjogren's syndrome, and a Japanese birth-cohort study tied higher maternal levels to lower childhood eczema, especially in girls.

These inverse results do not mean the chemical protects you. This is an exposure marker, not a simple 'good number, bad number' test, and different outcomes carry different associations for reasons that may include reverse causation, the way the body handles the chemical during illness, and confounding by diet or other exposures. The honest read is that outside of pregnancy and lipids, the health picture for this specific compound is still mixed and unresolved.

Why Blood and Urine Are Not Interchangeable

Long-chain PFAS like this one bind tightly to proteins in the blood, which is why blood has been the workhorse sample for studying them. Urine is a genuine elimination route for PFAS, but shorter-chain versions are far more likely to be cleared into urine than long-chain ones. In paired population data, long-chain PFAS were seldom detected in urine at all, which is a real limitation for reading a urine value of this compound.

That matters for interpretation. A urine value for this compound should not be assumed to mirror your total body burden the way a blood level might, and rules borrowed from other PFAS may not apply. In one Kyoto study, several PFAS fell as kidney filtration dropped, but this particular chemical did not follow that pattern, which shows it behaves somewhat differently from its relatives.

Why One Reading Is Not Enough

Because there are no standardized clinical thresholds for this chemical, a single measurement tells you little on its own. The real value comes from a trend: a baseline now, then repeat testing to see whether your level is rising, holding steady, or falling as you change your exposure.

There are no clinical guidelines that set retesting intervals for this chemical, so treat the following as a practical tracking rhythm rather than an evidence-based rule: establish a baseline, retest in 3 to 6 months if you are actively reducing exposure, then at least once a year. Because these chemicals persist and clear slowly, expect changes to be gradual rather than dramatic. Getting a baseline early gives you your own reference point to compare against as the science matures.

What to Do With an Unexpected Result

If your level looks high, the first step is not to panic but to look at patterns. Pair this result with a standard lipid panel and, if relevant, kidney function testing, since blood-fat and kidney context shape how the number should be read. If several PFAS are elevated together, that points toward a shared exposure source worth tracking down, such as drinking water or diet.

For anyone pregnant, planning pregnancy, or dealing with unexplained reproductive symptoms, an elevated result is a reason to review exposure sources with a clinician or environmental medicine specialist and to prioritize source control. Retesting over time, rather than acting on one value, is the right way to judge whether your changes are working.

When Results Can Be Misleading

• Sample type mismatch: most reference data come from blood, and long-chain PFAS are rarely found in urine, so a urine value cannot be directly compared to the blood-based studies that link this chemical to health outcomes.
• Kidney function: because urine reflects what your kidneys are clearing, changes in kidney filtration can shift a urine reading without meaning your total exposure changed.
• Lab method differences: PFAS testing is technically demanding, and background contamination or different lab techniques can affect the number, so results are most comparable when tracked at the same lab.
• Recent versus past exposure: it is not established how well a single urine value reflects recent intake versus years of accumulation, which limits what one reading can tell you.