Can you have both MCAS and POTS?

Yes, and it is common enough that the two plus hypermobility are frequently described together as a cluster. Co-occurrence is the expected pattern rather than a coincidence, which changes the framing from either-or to how much of each.

Where does hypermobility fit into this?

It is the third member of the cluster people describe, and it is a connective tissue trait that can be assessed clinically. Why the three appear together more often than chance predicts is not established, and the explanations offered are proposals. Worth mentioning to a clinician as part of the pattern rather than as evidence for either of the other two.

Does a normal standing test rule out POTS?

Not on its own. It is one measurement on one day, and the response to standing varies with hydration, illness, sleep and time of day. A negative recorded when you felt relatively well is weaker evidence than the same result on a bad day. It remains the most concrete thing available in this area, which is why it is still worth having.

Is it MCAS or POTS?

By BeatSIBO editorial team · Updated August 5, 2026

At a glance

Defined by
MCAS
Mediator release meeting criteria
POTS
A measured heart rate rise on standing
Objective number
MCAS
Only during a reaction
POTS
Yes, at the bedside
Cost to check
MCAS
High, with handling requirements
POTS
Low
Co-occurrence
MCAS
Expected
POTS
Expected

MCAS compared with POTS, on the dimensions that separate them
Dimension	MCAS	POTS
Defined by	Mediator release meeting criteria	A measured heart rate rise on standing
Objective number	Only during a reaction	Yes, at the bedside
Cost to check	High, with handling requirements	Low
Co-occurrence	Expected	Expected

The one that matters: These two and hypermobility appear together more often than chance predicts. Asking which one you have is frequently the wrong question.

Most pages framing this as a choice are asking the wrong question. These two are part of a recognised cluster, and the more useful question is how much of each is present rather than which one is real.

What actually separates them

The short answer

Postural orthostatic tachycardia syndrome is defined by a measurable event: a sustained heart rate rise on standing, without the blood pressure drop that would indicate something else. Mast cell activation syndrome is defined by mediator release meeting criteria. One has a concrete bedside test. The other has two competing criteria sets that disagree about who qualifies.

That asymmetry is worth acting on. In an area where almost nothing has a clean answer, a structured standing test is inexpensive, widely available, and produces a number.

Why co-occurrence is the expected pattern

The short answer

These two are frequently described alongside hypermobility as a cluster that appears together more often than chance predicts. Nobody has established why. Several mechanisms connecting mediator release to autonomic function have been proposed, and a proposed mechanism is not a demonstrated one. Treat the association as real and the explanation as open.

What is not settled here

The direction of any relationship here is unknown. You will find confident accounts online saying one drives the other, in both directions, usually from people selling a protocol aimed at whichever they claim is upstream. The literature does not support either ordering, and we are not going to pick one to make this page tidier.

Why gut symptoms appear in both

Autonomic function influences gut motility, and mediator release affects the gut directly. So gut symptoms are unsurprising in either, and very common in both together. That is part of why this cluster overlaps with the bacterial overgrowth picture, and why the guideline's caution applies here too.

Pimentel M et al., American Journal of Gastroenterology 2020 Clinical guideline

No single symptom can be specifically attributed to overgrowth. When three overlapping conditions all produce bloating and altered bowel habit, symptom pattern stops carrying diagnostic weight entirely.

What to do next

Get the thing that has a test tested. A structured standing test gives you a measurable result, and a measurable result is a much better foundation for a conversation with a clinician than a list of symptoms that fits four conditions.

Common questions

Can you have both MCAS and POTS?: Yes, and it is common enough that the two plus hypermobility are frequently described together as a cluster. Co-occurrence is the expected pattern rather than a coincidence, which changes the framing from either-or to how much of each.
Where does hypermobility fit into this?: It is the third member of the cluster people describe, and it is a connective tissue trait that can be assessed clinically. Why the three appear together more often than chance predicts is not established, and the explanations offered are proposals. Worth mentioning to a clinician as part of the pattern rather than as evidence for either of the other two.
Does a normal standing test rule out POTS?: Not on its own. It is one measurement on one day, and the response to standing varies with hydration, illness, sleep and time of day. A negative recorded when you felt relatively well is weaker evidence than the same result on a bad day. It remains the most concrete thing available in this area, which is why it is still worth having.