In pediatrics, almost all of our patients are healthy. We’ve got some doozies of special-needs kids, but by-and-large your ordinary pediatric patient is doing well, and does not need extensive testing or elaborate procedures to ensure good health.

Still, we do run across some occasional problems. Some children have poor vision, or hearing problems, or kidney disease, or hypothyroidism. Or autism, or Tay-Sachs Disease, or a penny up their nose. A whole lot of what we do in our checkups is easy, cheap, and quick tests to screen for these and many other problems.

Just a taste:

• We look at height. If junior is gaining height as expected, he almost certainly doesn’t have hypothyroidism.
• We look at blood pressure. If it’s normal, kidney disease is less likely.
• We look in noses. Usually you can see a penny up there.
• We test vision, using either an electronic screener, or an old fashioned chart-on-the-wall chart. Low tech, but it still works — reading the “big E” and those letters underneath is a very good screening test for vision problems.

But here’s the catch: The low tech, cheap screening tests done at the pediatrician’s office aren’t going to diagnose these conditions. They’re not meant to. These are screening tests, designed to separate the truly low-risk child from children at higher risk for genuine disease.

Children who have an elevated blood pressure are at higher risk for kidney disease — but most of them, still, don’t actually have kidney disease. Children who are growing shorter than expected might have hypothyroidism, but they probably don’t. And children who fail the vision screen may well, in fact, have good vision. But all of these children, who fail the initial screen, need more evaluation to make sure there isn’t something important going on.

Sometimes we do a poor job explaining this to parents. If your child failed our hearing screen, it doesn’t mean he is deaf, or that he even definitely has a hearing problem: It just means he might have a hearing problem, and needs further evaluation. Maybe a retest, or a more-thorough hearing test at an audiologist. The follow-up testing might be normal, and that would be good news.

We’ve had some parents getting angry when their follow-up tests are normal: “It was a waste of time and money! We didn’t need to go to the eye doctor!”

Well, I’m sorry if we explained that poorly. A screening test is a screening test. I can’t say for sure whether junior really needs glasses, but I can say which kids need more evaluation. I don’t think a thorough eye exam that ends with a reassuring result is a waste of time.

Why screen at all? I mean, why not just have every child undergo a thorough eye test at the ophthalmologist, and a full audiology exam, and an EKG and echocardiogram and renal ultrasound and every blood test in the book and a weekly whole body MRI and a two week intense neuropsychiatric evaluation and brain biopsy? Because that would be expensive, and that would be torture, and it still wouldn’t rule in or out every possible disease.

Look at it this way: If we set the bar so high that everyone who failed the screen really had disease, that would mean many people who didn’t fail the screen really do have disease. In an inexact world, you can’t have it both ways. There’s a grey zone there, and screening tests are designed to catch children who “might” have disease, meaning they also catch kids who really don’t. Screening tests aren’t meant to confirm disease. They’re meant to catch the kids who need more evaluation to be sure they’re fine.

Roy Benaroch is a pediatrician who blogs at The Pediatric Insider. He is also the author of Solving Health and Behavioral Problems from Birth through Preschool: A Parent’s Guide and A Guide to Getting the Best Health Care for Your Child.