Dear Doctor: Whenever I offer a certain friend a ride, she kindly declines, explaining that, because I have Type 1 diabetes, she's afraid my blood sugar will suddenly crash and I'll get into an accident. I know it's just ignorance and try not to be insulted. Can you help explain why most people with diabetes are OK to drive?

Dear Reader: It's true that people living with Type 1 diabetes run the risk of hypoglycemia, which is when blood sugar becomes dangerously low. This can lead to physical reactions that would make driving dangerous.

The early warning signs of hypoglycemia include shakiness, dizziness, hunger, mood swings, headache, sweating and anxiety. If left untreated, hypoglycemia can lead to blurred vision and slurred speech, jerky or uncontrolled movements, confusion or muscle weakness. At its most extreme, it can cause seizures or convulsions and result in death.

However, when diabetes is properly managed, serious episodes of hypoglycemia tend to be infrequent. The majority of people with Type 1 diabetes who adhere to specific safe-driving guidelines drive regularly without medically related incidents. By remaining vigilant about blood glucose monitoring and being prepared for a quick correction by eating a fast-acting sugar snack, most people with diabetes can successfully manage an episode of hypoglycemia.

We agree that your friend's fears stem from a lack of knowledge about diabetes. Perhaps learning about the precautions set out by the American Diabetes Association, with an eye to helping people with diabetes live full and safe lives, will give your friend some peace of mind?

-- Before you set out on a drive, check your blood glucose. On longer trips, it's important to stop and do periodic checks to be sure you're in the optimal range.

-- Make it a habit to stock the car with a special driving kit. Include your blood glucose meter and lots of snacks, including several that are quick-acting sources of sugar. Hard candy, fruit juice or glucose tablets will do the trick.

-- Are you feeling any of the signs of hypoglycemia during your drive? Pull over immediately (seriously, immediately, because things can go wrong so quickly), and check your blood glucose level.

-- Is your blood glucose low? That's the time for one of those fast-acting sugar sources. Take a 15-minute break and do another check. If you're in the zone, it's OK to start driving again.

-- It's very important to stay current on eye exams, so you can catch any diabetes-related vision problems as quickly as possible.

There is one very important caveat.

If you have experienced an episode of hypoglycemia unawareness, which is when you are unable to detect the warning signs that your blood glucose is low, you must give up driving until awareness has been re-established. This is for your own safety, and for those around you. Call your doctor to talk about treatment strategies.

So ask yourself: Is your diabetes under control? Are you able to quickly detect and promptly respond to an episode of hypoglycemia? Will you follow the ADA's driving guidelines? If so, you can reassure your friend about your ability to take the wheel.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: My doctor at the local bone and joint clinic said I was a good candidate for an experimental injection of PRP for arthritis in my right shoulder. What is your opinion? I'm 71.

Dear Reader: Unlike your doctor, I'm not familiar with your medical history or your shoulder condition, so I can't offer a specific medical opinion. What I can do is explain a bit more about this procedure and its potential.

First, some background: Because tendons, ligaments and cartilage have limited blood flow, the body's ability to repair them is limited. Autologous platelet-rich plasma (PRP) aims to compensate for this. It's prepared by removing about 30 to 60 cubic centimeters of blood from your arm. The blood is then filtered through a process called plasmapheresis, which concentrates the platelets. The wonderful thing about platelets is that they're usually the first blood component to arrive at the site of an injury, bringing molecules that encourage healing. Thus, platelet injections have the potential to improve healing of an area with normally poor blood flow.

Most studies of PRP for the shoulder have involved people having surgical repair of the joint, with surgeons using PRP to bolster a rotator cuff repair or to boost healing after shoulder replacement. A 2015 study combined data from eight studies comparing arthroscopic surgery for rotator cuff tendon tears with PRP and without PRP. Of 464 patients, 234 had PRP injections. The authors found no difference in the rates of tendons re-tearing after surgery, nor did they find any significant MRI changes in the PRP group. Further, the studies did not find any difference in range of motion or pain with the use of PRP.

Another 2015 analysis -- this one of 11 studies with a total of 597 patients -- also failed to show MRI or symptom benefit with the use of PRP. However, PRP did show benefit among people who had rotator cuff tendon tears greater than 3 centimeters. A 2016 study showed benefit in the use of PRP in the first month after surgery, but no significant benefit after six months.

Also, there are small studies that show PRP can help people who are not having shoulder surgery. Some studies have compared PRP to steroid injections in the shoulder for partial rotator cuff tears or for impingement syndrome and found that PRP was equivalent or even more helpful than steroid injections. However, a study from Iran found that while PRP did ease pain and improve mobility of the shoulder, it was not superior to physical therapy.

As for arthritis of the shoulder, I haven't found good studies to support the use of PRP. Some studies show benefit for arthritis of the knees, but their poor design and lack of comparison subjects make conclusions difficult.

That said, while I don't know the degree of your shoulder arthritis, if you have impingement of the shoulder or a partial tear of your rotator cuff tendon, PRP in addition to physical therapy may have benefit.

I'm with your doctor on this: It's worth a try.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: I've seen a lot of dogs recently in grocery stores and restaurants wearing those yellow service dog vests, but some of them can't obey even simple commands like "sit" and "stay." They seem to really be pets. What do trained service dogs do? Whom do they help?

Dear Reader: It's a shame when dog owners misrepresent their pets as service animals. No doubt some are legitimate "emotional support" animals, necessary companions for their owners to be able to spend time in public spaces. But federal law states that a service dog is one that has been specially trained to physically assist a person with a disability, including -- and we're quoting the law here -- "a physical, sensory, psychiatric, intellectual or other mental disability."

It is on that basis that these devoted animals are granted access to venues and areas not open to other pets. With their rigorous training and specialized skills, service dogs open up the world for their handlers, and keep them safe within it.

Service dogs perform hundreds of tasks for more than a dozen types of disabilities. We're all familiar with guide dogs, which help people with impaired vision. They lead their handlers around obstacles like a park bench, a low-hanging awning or a hole in the ground. They warn them of changes in elevation, like a curb or the edge of a subway platform. They can follow a designated person, like a waiter in a restaurant, or find their handler an empty seat in a public space. And though their handlers are the decision-makers in the partnership, guide dogs have been taught "intelligent disobedience." When given a command to walk forward, if danger is present, like a sudden drop-off or oncoming traffic, they will refuse.

For people with impaired hearing, specially trained dogs become their ears. With a touch of their nose or a gentle paw, they can signal a ringing telephone, a crying baby, a smoke alarm, an alarm clock, a family member calling the handler's name, computer beeps, cellphone alerts and a person's arrival.

People with physical disabilities or missing limbs rely on their service dogs to help with mobility. These dogs can pull a lightweight wheelchair, offer assistance by bracing their handlers as they get up or down, and help their handlers rise if they should fall down. They can open doors, turn light switches on or off, and pick up objects as small as a dime.

Seizure dogs, which are trained to recognize their handlers' physical symptoms, can summon help by calling 911 via a special life-alert system, or provide physical stimulation. Like many service dogs, they are trained to retrieve medication. Diabetic alert dogs use their sense of smell to detect episodes of high or low blood sugar and warn their owners. Severe allergy alert dogs let their handlers know about life-threatening allergens nearby.

Service dogs are remarkable in their training and dedication. And though it's tempting to give them a pat or say hello, please don't. Service dogs out in public are at work. Correct etiquette is to ignore them, so they are not distracted from their job.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)