Four in five U.S. medical bills contain at least minor mistakes — costing the nation $68 billion annually in unnecessary healthcare spending by doctors and patients alike.

That’s the key finding of a new analysis by MHS (Medliminal Healthcare Solutions), an organization that helps patients find and fix medical billing errors.

MHS CEO Jim Napoli says such mistakes have become the rule and not the exception for American consumers, for a variety of reasons.

“For years we had found that approximately eight in 10 hospital bills we receive contain numerous overcharges,” Napoli says, “but now that figure is closer to nine in 10.”

What’s behind most errors: Healthcare industry standards are changing and physicians, and their office staffers, often lack necessary training in new medical coding. That means many don’t classify a patient's diagnosis into medical numeric codes that are required for doctor’s offices to seek insurance of government reimbursement for services.

In addition, some healthcare providers inflate costs for products and services, or engage in what’s called “cost shifting” — charging paying or insured Americans more to balance out coverage for uninsured or poor patients who can’t pay for the services they receive

David Womack, president and CEO of the Practice Management Institute (PMI), says the risks are not just financial. In fact, medical billing errors can result in poor care, injury, or even the death of a patient.

“The tide is changing and proper coding certification will become the healthcare standard within 5 years,” says Womack, arguing that hiring certified office staff to ensure a doctor’s practice operates competently and ethically is “no longer a suggestion, but a requirement.”

Womack — whose organization helps provide training to medical staff, physicians, and hospital systems — says professional certification in medical coding, third-party billing, office management, and compliance, can help turn the tide on rising medical billing errors. It can also help physicians focus more attention on patient care, and less on book-keeping issues.

Patient advocates also urge consumers to be on the lookout for common errors that appear in as many as four out of five medical bills.

Experts advise bringing a healthy skepticism to any medical bill you receive and carefully check for common errors to make sure you are not being overbilled or wrongly charged.

After any medical visit, you should receive an invoice telling you how much you owe. But be sure to request an itemized bill or statement from the hospital or your doctor to check each service you are being charged for.

If you have health insurance, you should also receive what’s called an “explanation of benefits” (EOB) statement from your health plan. The EOB should provide details such as the type of service received, the date of service, the amount your healthcare provider billed your insurance company, the total amount that was not covered and the total patient cost.

According to the consumer group, Nerd Wallet, here are the eight most common billing errors to watch out for when you receive your itemized bill and EOB statement:

Duplicate charges: Check for duplicate charges to make sure you were not billed twice for a service or procedure. With an itemized bill, it should be much easier to spot.

Canceled tests or procedures: Patients are sometimes charged for a test or procedure that were ultimately canceled. If you think you were wrongfully overbilled, collect all the necessary documents to prove that you did not receive the service, and dispute the charge.

Incorrect patient information: Small errors — incorrect name spellings or policy number misprints — are common on medical bills. If your insurance ID number is wrong, it can lead to a claim denial or a full amount sent out by your health plan.

Upcoding charge: A hospital may fraudulently inflate a patient’s diagnosis to one that represents a more serious procedure, leading to a higher medical bill. For example, you may have received the lowest level of emergency room services but be billed at the highest level. This is an illegal, fraudulent practice, and you should ask your healthcare provider to correct the charge immediately.

Unbundling of charges: This is when separate charges are billed to you that should have been filed under one procedure code. This type of mistake can inflate costs to you, but is tricky to identify. If you suspect such a mistake on your bill, you can reference the National Correct Coding Initiative by the Centers for Medicare and Medicaid Services for help.

Balance billing when in-network: This occurs when a doctor or hospital bills you for charges other than co-payments, co-insurance, or any other amount than what was assigned by your insurance company. Balance billing is often improper when the care was provided by an in-network hospital or physician. If you think you’ve been balance billed, compare the bill with your EOB to make sure.

Incorrect quantity: Check for incorrect quantities of items or medications on your bill. This mistake could be as simple as an extra “0” placed at the end of a number by the billing department — 100 pills instead of 10, for example.

Operating room and anesthesia time: If you have undergone surgery, check your medical records to see how long you were in the operating room or under anesthesia. Because patients are usually billed in 15-minute increments in these instances, mistakes here can add up quickly.

In addition to checking for medical bill errors MHS recommends checking for potential price gouging. Among the sample items and charges the organization has found on its clients' medical bills:

• One alcohol swab: $23.
• Medicine cup (the small, paper cup; not the actual medicine): $18.
• One pair non-sterile gloves: $53.
• A small piece of gauze: $20.
• Sanitary napkin (just one): $16.

Consumers should also view as suspect any charges that are vaguely identified — such as a $2,000 charge for medical supplies or "miscellaneous" services.