The Medical Tests Behind a POTS, MCAS or hEDS Diagnosis: A Plain-Language Guide

😰 Walking into testing blind is its own kind of stressful

Somebody mentions a "tilt-table test" or a "tryptase panel" and hangs up the phone, and suddenly you're googling at 11pm trying to figure out what's about to happen to your body. If you're anywhere in the diagnostic process for postural orthostatic tachycardia syndrome (POTS), mast cell activation syndrome (MCAS) or hypermobile Ehlers-Danlos syndrome (hEDS), here's a plain-language walkthrough of the tests that actually come up — what each one measures, roughly what to expect, and why the process can feel so slow.

💓 Testing for POTS

Active stand test. The most commonly used first screen. Your heart rate and blood pressure are measured after you have been lying down, then again at intervals during 10 minutes of standing. Clinicians look for a sustained heart-rate increase of 30 beats per minute or more in adults, or 40 or more for ages 12 to 19, without a significant and sustained drop in blood pressure.

But the heart-rate change alone does not diagnose POTS. It must occur alongside frequent orthostatic symptoms that worsen while upright and improve when lying down, have been present for at least three months, and are not better explained by another condition or medication. A significant sustained fall in blood pressure — 20 mmHg systolic or 10 mmHg diastolic — points towards orthostatic hypotension rather than POTS. This pattern supports POTS only when it occurs with chronic orthostatic symptoms and other causes have been excluded.

The active stand test can also miss some cases, so a normal result is used cautiously rather than as a definitive exclusion.

Tilt-table test. Used when the active stand test is inconclusive, or a more controlled reading is needed. You're strapped to a table that slowly tilts you upright while heart rate, blood pressure and sometimes oxygen levels are monitored continuously. It isn't painful, but the lightheadedness and fatigue afterward are real — most people plan a low-key rest of the day around it.

One preparation point that matters. Tilt and stand protocols vary between centres, and medications can either cause or mask an abnormal response — so whether a medicine should be continued or withheld depends on the clinical question being asked. Follow the testing centre's preparation instructions, and do not stop medications unless the ordering clinician or testing centre tells you to.

Ruling other things out. The formal criteria require excluding other causes of a fast heart rate on standing — anaemia, thyroid problems, dehydration, fever, pain, certain medications, and severe deconditioning among them. This is why bloodwork often accompanies the assessment, and why it isn't a sign your doctor doubts you.

🔗 Want more like this? Browse all our POTS guides →, MCAS guides →, or hEDS guides →

🌸 Testing for MCAS

MCAS testing has a reputation for being frustrating, and there's a real reason for that: many of the chemical markers mast cells release degrade quickly, so timing is everything.

Serum tryptase is the most stable marker and the one most labs can run reliably. The diagnostic pattern isn't just "high tryptase" — it's typically a rise of at least 20% above your own baseline, plus 2 ng/mL, measured within 1 to 4 hours of a flare, compared against a baseline level drawn when you're feeling well.

Emergency treatment is based on symptoms and should not wait for test results. A normal tryptase does not rule out anaphylaxis or mast-cell activation. Equally, symptoms alone cannot confirm MCAS: diagnosis requires typical recurring symptoms, a measurable rise in a mast-cell mediator during an episode, and improvement with appropriate treatment, while other possible causes are considered. Diagnosing MCAS requires the full clinical and laboratory criteria.

Urinary N-methylhistamine and prostaglandin D2 metabolites may also be tested, usually from a urine sample collected during or shortly after a reaction. The collection timing depends on the specific test and the laboratory running it, so follow the instructions you're given rather than a general rule. These are supporting tests rather than proof of MCAS on their own, and results can be affected by sample handling and by certain medications.

Because of this timing sensitivity, a single "normal" panel drawn on a calm day doesn't rule MCAS out — which is a big part of why the diagnostic process can take multiple flare-timed attempts to capture.

🦴 Testing for hEDS

This is the one test in the trifecta that isn't really a lab test at all. Hypermobile EDS (hEDS) is the only EDS type without an identified genetic marker, so it cannot be confirmed with a genetic test and diagnosis relies on clinical evaluation.

Genetic testing may still be used if the history or examination suggests another type of EDS, or a different inherited connective-tissue condition — so being offered it doesn't mean your clinician has changed their mind about hEDS.

Beighton score. A 9-point hands-on exam checking how far certain joints — thumbs, pinkies, elbows and knees — and the ability to place the palms flat on the floor with straight knees extend beyond a typical range. Scores are interpreted using age-specific cut-offs. If someone is one point below the cut-off, clinicians may use a five-question history to look for previous hypermobility, since flexibility can decrease with age or after injury.

2017 hEDS diagnostic criteria. The Beighton score is only one piece. The full criteria have three parts assessed together: generalised joint hypermobility, a combination of systemic and musculoskeletal features — such as skin findings, joint instability and family history — and the exclusion of other conditions that can also cause hypermobility. If someone has symptomatic hypermobility but does not meet the full hEDS criteria, a hypermobility spectrum disorder (HSD) may be considered. The Ehlers-Danlos Society publishes the checklist that clinicians use — it is freely available, and some people find it useful to read before an appointment.

⏳ Why the whole process can drag on

None of this is in your head, and none of it means you're doing something wrong. Diagnostic delay is a well-documented feature of all three conditions — the published figures vary a lot depending on which population is studied, but they are consistently measured in years rather than months, and often involve several specialists before anyone connects the picture. The reason is structural: awareness of these overlapping conditions is still uneven across specialties, and each one sits in a different clinic.

Bringing a symptom log, asking specifically about active stand testing or a Beighton exam by name, and requesting mast cell testing be timed around a flare rather than a routine visit are all things patients report help move things along faster.

❓ Frequently asked questions

📚 Sources & further reading

The information in this article is drawn from the following sources. We encourage you to explore them.

• Raj SR, Fedorowski A, Sheldon RS — Diagnosis and management of postural orthostatic tachycardia syndrome. CMAJ. 2022;194(10):E378–E385 (full POTS criteria, including symptom duration and the exclusion of orthostatic hypotension)

• Thijs RD, Brignole M, Falup-Pecurariu C, et al. — Recommendations for tilt table testing and other provocative cardiovascular autonomic tests. Clin Auton Res. 2021;31:369–384 (protocol variation and medication handling)

• Weiler CR, Austen KF, Akin C, et al. — AAAAI Mast Cell Disorders Committee Work Group Report: MCAS diagnosis and management. J Allergy Clin Immunol. 2019;144(4):883–896

• Aziz Q, Harris LA, Goodman BP, et al. — AGA Clinical Practice Update on GI Manifestations and Autonomic or Immune Dysfunction in Hypermobile Ehlers-Danlos Syndrome. Clin Gastroenterol Hepatol. 2025;23(8):1291–1302 (targeted rather than universal testing)

• The Ehlers-Danlos Society — hEDS Diagnostic Checklist (the 2017 International Classification criteria)

• Dysautonomia International — Postural Orthostatic Tachycardia Syndrome (active stand test and tilt-table testing)