President Donald Trump celebrates the passage of the American Health Care Act through the House with Republican representatives on Thursday. REUTERS/Carlos Barria The American Health Care Act, the GOP plan to overhaul the US healthcare system, passed in the House on Thursday.

What counts as a preexisting condition that could get you denied coverage under the new plan?

A lot.

The bill raises concerns, especially from patient advocacy groups and physicians, that under the AHCA, people with preexisting conditions would once again find health insurance inaccessible.

A preexisting condition is a term insurance companies used before the Affordable Care Act, the healthcare law better known as Obamacare, to classify certain diseases or health problems that could cause a person to be denied coverage or make their coverage more expensive than that of people considered healthy.

Before the ACA

The Kaiser Family Foundation estimates that 27% of Americans under 65 have health conditions that could leave them without access to insurance. Some of the preexisting conditions that insurers declined coverage because of before the ACA, according to the foundation, include diabetes and heart disease, which affects millions of Americans.

These preexisting conditions include:

AIDS/HIV, lupus, alcohol abuse/drug abuse with recent treatment, severe mental disorders such as bipolar disorder or an eating disorder, Alzheimer's/dementia, multiple sclerosis, rheumatoid arthritis, fibromyalgia and other inflammatory joint disease, muscular dystrophy, cancer, severe obesity, cerebral palsy, organ transplant, congestive heart failure, paraplegia, coronary artery/heart disease, bypass surgery, paralysis, Crohn's disease/ulcerative colitis, Parkinson's disease, chronic obstructive pulmonary disease/emphysema, pending surgery or hospitalization, diabetes mellitus, pneumocystis pneumonia, epilepsy, pregnancy or expectant parent, hemophilia, sleep apnea, hepatitis C, stroke, kidney disease, renal failure, transsexualism.

Other conditions that could make it harder to purchase a health insurance plan, according to KFF:

Acne, allergies, anxiety, asthma, basal cell skin cancer (a type of skin cancer that doesn't tend to spread), depression, ear infections, fractures, high cholesterol, hypertension, incontinence, joint injuries, kidney stones, menstrual irregularities, migraine headaches, being overweight, restless leg syndrome, tonsillitis, urinary tract infections, varicose veins, and vertigo.

Some insurance plans before the ACA also counted rape and domestic violence as preexisting conditions, though CNN reports that some states have banned that practice.

President Barack Obama signs the Affordable Care Act into law in March 2010. Associated Press/Charles Dharapak

Under the ACA

One of the critical parts of the ACA was that it prohibits insurers from denying coverage to or charging more for people with preexisting conditions. That has been in effect since 2014.

That means that if you had any of those conditions listed above — asthma, for instance — you still could have the same insurance as someone who had a clean bill of health and someone who is a cancer survivor, pregnant, or obese.

How preexisting conditions could return

The version of the AHCA that just passed in the House includes the MacArthur amendment, which would allow states to avoid some of the regulations imposed by the ACA. Experts say that could weaken the regulations around preexisting conditions.

Republicans, on the other hand, say the bill would protect people with preexisting conditions.

"The amendment is very clear: Under no circumstance can people be denied coverage because of a preexisting condition," House Speaker Paul Ryan said in a release.

But the difference between being denied coverage and not being able to afford coverage is the gray area that has people concerned.

"The various patchwork solutions offered by lawmakers would still leave the millions of patients we represent, who have serious and chronic health conditions, at risk of not being able to access life-saving treatments and care," a group of 10 patient advocacy organizations said in a release on Wednesday.

The bill now heads to the Senate. Republican senators have signaled they would scrap the AHCA and come up with a bill of their own.