Physical complaints can be difficult to articulate, especially when they are vague or intermittent. Like a car’s problems that vanish when you take it to the mechanic, symptoms often elude us when we’re at the doctor’s office. But when you can’t explain your symptoms, you increase the chances of unnecessary tests, needless trial-and-error treatments and even misdiagnosis.

Orly Avitzur, medical adviser to Consumer Reports, finds it much tougher to get at the root of a problem when a patient tells her that she has “trouble walking and it hurts all over” than when she provides a clear description, such as: “Over the past six months, I’ve had low-back pain and heaviness in my legs that gets worse after I walk two blocks, then improves when I sit down.”

Though it’s sometimes difficult to express why, when or even where you hurt, knowing which questions your doctor will ask — and thinking about how to answer them — can help you get a quick, accurate diagnosis. Avitzur offers this advice on how to prepare for your office visit:

Use the alphabet formula

Your doctor will ask for several pieces of information. To figure out how to answer, remember the letters O-P-Q-R-S-T and jot down the answers before your appointment.

Onset. When did the symptoms start, and what were you doing at the time? Was the onset gradual, sudden or a worsening of a chronic complaint?

Place. Where does it hurt?

Quality. What type of discomfort is it? Sharp, stabbing, dull, achy, cramping, pulling, squeezing or something else?

Radiation. Does the pain radiate to another part of the body? The answer can be a tip-off for your doctor. For example, a sudden, crushing chest pain that moves to the jaw can be a red flag for a heart attack; pain in the upper abdomen (particularly on the right side) that travels to the back and right shoulder may signal gallbladder problems.

Severity. How severe is your pain on a 10-point scale, with 0 being no pain; 5, moderate pain; and 10, the worst possible pain? Though the perception of pain varies a great deal from person to person, that scale is useful for assessing your pain over time (e.g., it began at a 3, and two days later, it’s a 9) and to describe how effective a treatment may be (the pain was a 5, but after you took acetaminophen, or Tylenol, it receded to a 1).

Time and triggers. How long have you had the symptom? How often does it occur, what is its duration, and does its intensity fluctuate? Is it more common at a certain time of day? Does something bring it on or make it worse? Is it present at rest or only with movement? Is it affected by activities such as walking, eating, getting out of bed or climbing stairs?

Keep a symptom diary

Identifying triggers can be challenging. Avitzur often asks patients with migraines to track their headaches in a journal, online or in one of the mobile apps available for this purpose. That helps reveal patterns that casual observation might miss.

When the diary includes detailed attention to diet, for example, patients may discover a clear link between their symptoms and eating specific foods. Other patients discover a connection with weather, realizing that their migraines correspond to changes in barometric pressure. And many women find a correlation with their menstrual cycles that is so precise that they can actually treat them preventively on vulnerable days. Diaries also help in tracking non-pain symptoms, including those related to allergies, asthma, heart failure, Parkinson’s disease, psoriasis and many other conditions. Because you are not depending solely on memory, your doctor gets a more accurate view.

Take a picture or video

In medicine, a picture truly is worth a thousand words. Photographs and videos record physical findings — intermittent rashes, tremors or muscle twitches — and can document an infection after surgery. That visual evidence will speak to your doctor much more directly than even the most eloquent verbal description.

Copyright 2014. Consumers Union of United States Inc.

For further guidance, go to www.ConsumerReports.org/Health, where more detailed information, including CR’s ratings of prescription drugs, treatments, hospitals and healthy-living products, is available to subscribers.