Imagine going to a public hospital’s emergency department and a nurse from a private hospital asks you if you want to go to there instead.This is the basis of a trial arrangement with a Ramsay Health Care nurse embedded at a Queensland public hospital emergency department. The idea is to divert privately insured patients to a Ramsay private hospital, reducing pressure on the public system.But there are concerns about giving a single company access to emergency department patients and because being transferred to the private system could lead to unexpected costs for patients.So, in an emergency, what does your private health insurance actually cover? And when does Medicare or other government funding foot the bill?The ambulance tripPrivate health insurance does not automatically include ambulance cover. Some insurers offer stand-alone ambulance cover, or you can check if you can add it to your hospital or extras policy.But the state governments of Queensland and Tasmania cover ambulance trips for their residents.Medicare doesn’t cover an ambulance trip. So if you don’t have ambulance cover and live in Victoria, New South Wales, South Australia, Western Australia, Northern Territory or Australian Capital Territory you will receive a bill. This can include a base call-out fee plus a charge for every kilometre travelled. For example, in Victoria, an emergency metropolitan road trip by ambulance costs A$1,477 and a regional trip $2,179. There are usually exemptions for concession card holders and pensioners.In a public hospital emergency departmentYou cannot use your private health insurance in the emergency department of a public hospital (or at an urgent care clinic). You don’t need to anyway as Medicare covers those. And having private cover will not get you seen any faster.However, public hospital emergency department staff may ask if you have private health insurance in case you are later admitted to a hospital ward as an inpatient. If you choose to be admitted as a private patient, the public hospital can bill your health fund for your accommodation, which helps bring money into the public hospital system. You may be able to choose your treating doctor if they are available.However, choosing private status in a public hospital does not get you treated faster or guarantee you a better room. Whether it is worth using your insurance here depends entirely on your specific policy and whether the hospital and your insurance company guarantee you will have no out-of-pocket costs.If you are treated in a public hospital emergency department and sent home without being admitted, your private insurance does not come into play at all. Read more: If you’ve got private health insurance, the choice to use it in a public hospital is your own In a private hospital emergency departmentGoing to a private hospital emergency department, whether you go yourself or are transferred under a special arrangement, is a completely different situation. This is where there can be major out-of-pocket costs.Private health insurance hospital cover only activates after a doctor formally admits you into a hospital ward. Until then, you are considered an outpatient, and your health fund pays nothing toward your emergency department visit.So if you are assessed, treated and sent home directly from a private hospital emergency department, you must pay the full bill yourself. This includes a facility fee, often $300–$500 just to walk through the door, plus extra costs for doctors, X-rays, blood tests or medication. A straightforward visit can easily cost several hundred dollars, while complex cases can be more than $1,000.If you’re admitted to a private hospitalIf a doctor decides you need to be formally admitted to a private hospital, either from the emergency department or for a planned procedure, your hospital cover then kicks in.Your fund broadly covers the cost of your hospital room, operating theatre fees and nursing care. However, it might not cover the full costs of specialist fees. Surgeons, anaesthetists and other doctors often charge more than the standard government rate listed on the Medicare Benefits Schedule. The difference between what they charge and what your fund pays is called the gap, and you have to pay it out-of-pocket. Some procedures may not be covered at all depending on your level of cover. Most private policies also require you to pay an excess. This is a fixed amount for your admission, such as $500 or $750, before the fund pays the rest. Before any treatment, always ask your doctor for a breakdown of costs and whether they have an agreement with your specific health fund.What’s the take-home message?In a medical emergency, Medicare is your primary safety net. You will get free care in every public hospital emergency department (and at urgent care clinics).If you choose to go to a private hospital emergency department, ask the staff if you will be formally admitted to a ward or treated as an outpatient. The answer determines whether your insurance pays the bill or you pay it yourself. Finally, check your ambulance cover today, before you ever need to call 000.Yuting Zhang has received funding from the Australian Research Council, Department of Veterans' Affairs, the Victorian Department of Health, National Health and Medical Research Council, and Eastern Melbourne Primary Health Network. In the past, Professor Zhang has received funding from several US institutes including the US National Institutes of Health, Commonwealth fund, Agency for Healthcare Research and Quality, and Robert Wood Johnson Foundation.