Lab tests aren’t always helpful–here’s why:

Medicine is always changing, and in many ways, that’s a good thing. While many diagnoses can be made by asking a few questions and performing a thorough physical exam, ordering laboratory and imaging tests is a crucial part of modern medicine. These tests allow us to catch previously fatal diseases early, to choose appropriate treatments, and to help families know what to expect. Those sound like great things–and in many cases, they are.

If our tests were perfect (and free) there would be little reason for concern. But nothing in life is perfect (or free), so sometimes things get complicated. Especially because–when ordered or interpreted inappropriately–tests can result in expensive bills, unnecessary procedures, confused patients, and even more confused doctors. The fact that we can order a test doesn’t mean that we should. So while parents don’t typically decide which tests to order, it’s useful for them to understand a few important limitations:

  • Sometimes, there’s no test. Despite some pretty amazing medical advances, we can’t always live up to our patients’ expectations. Parents often want information about their child’s current condition or future prognosis that we just can’t provide until we’re looking back years later. Heck, we can’t even predict what color their eyes will be.
  • Tests require interpretation. When lab results come back, they usually don’t provide a complete picture. For instance, a low hemoglobin level could be a sign of a nutritional deficiency, a red blood cell disorder, GI bleeding, cancer, heavy menstrual periods, or a number of other problems. Test results are like puzzle pieces; they require someone to put the information together using a knowledge of what the values mean, the disease processes that can affect them, and–most importantly–the patient that donated the sample.
  • Context is everything. Even tests that we think of as being a simple yes/no answer can require some thought. A positive pregnancy test in a sexually-active 26-year-old woman is very different from the same result in a post-menopausal woman. Or a man. When tests are used inappropriately, the answers they provide may not mean what you think they do.
  • “Normal” isn’t always normal. This comes up a lot in pediatrics. The laboratory values we expect to see in a newborn are frequently different from the expected values for adults. For example, a bilirubin level of 14 in a 5-day-old infant is expected. In an older child or adult (or a 1-day-old infant), it should raise some serious concerns. There are plenty of cases where–for a particular patient–an “abnormal” value is what we should expect…or where a “normal” value should be very concerning.
  • No test is perfect. In fact, some of them are pretty much useless. But even good tests will sometimes provide inaccurate results. Some tests tend to have more false positive results (positive tests without true disease); others tend to err on the side of false negatives (missing an actual problem). I could drone on for hours about statistics, but here’s the main point: every test has unique properties that guide when we should use it and how we should interpret the result, and these properties are almost as important as the result itself.
  • Tests cost money. Lots of money. Estimates vary, but those who know healthcare will tell you we waste billions of dollars every year on unnecessary tests. A rapid strep test or chest x-ray may not seem like a big deal, but the costs multiply quickly when you look at a whole population. Many tests are also potentially harmful, requiring the use of radiation, contrast, or invasive procedures. And often, a single abnormal result leads to a long, expensive, and confusing search for increasingly rare diagnoses–just to find that the only problem was the lab result. 
  • Tests often lead to treatments. Abnormal laboratory values frequently lead to treatments–after all, that’s usually why we ordered them. These treatments may save someone’s life, provide relief from symptoms, or improve someone’s quality of life. But sometimes test results lead to unnecessary treatment for a “problem” that never existed or that would have gone away on its own. And just like tests, treatments aren’t perfect; every treatment carries some level of risk, so ensuring that we test and treat only when we should is part of practicing conscientious medicine.
  • Often, the answer doesn’t matter. In my hospital, we have the ability to run a test from a nasal swab that can identify about a dozen of the most common respiratory viruses. In certain circumstances, it’s a very useful test. (It’s also very expensive.) But while some parents would love to know the exact name of the virus causing their child’s runny nose, it usually wouldn’t change my treatment at all. Unless the answer might actually matter, the question probably isn’t worth asking.

But sometimes tests are extremely helpful. There are endless examples of test results that have changed a patient’s treatment in truly meaningful–sometimes even life-saving–ways. Here are some examples of how tests can be useful:

  1. To screen for potential problems. A great example is the newborn screen sent soon after a baby’s birth. The point is to identify diseases that are treatable, relatively common, and cost-effective. It doesn’t make sense to spend $100,000 to look for a 1-in-a-million disease that we can’t do a thing about. But for diseases where we can really make a difference in a child’s life by intervening early, it’s extremely valuable information.
  2. To rule out dangerous conditions. A child with a head injury may need a CT scan to look for brain bleeding. A child with severe abdominal pain may require imaging, blood tests, or even a surgical procedure to look for life-threatening problems. Sure, these procedures all carry risks, but sometimes those risks are worth taking to rule out (or confirm) a serious diagnosis.
  3. To guide treatment. This is one of the most common reasons that doctors order tests. This may mean deciding when to treat with antibiotics, when to do a blood transfusion, or whether to make a number of other decisions.  Pediatricians often order tests to look for strep throat, urinary tract infections, or other problems. The assumption, of course, is that the result will affect the doctor’s decision about whether to treat a condition, or what treatment to use.
  4. To establish a prognosis. Prognosis is a step beyond diagnosis. It’s not what a patient has, but what we should expect. It can be as grim as life expectancy from cancer, or as mundane as how long a fever can be expected last. But when it’s important for us to know where a patient is headed, sometimes the right test can help answer the question.
  5. To get treatments covered. In an age when insurance companies control pretty much everything we do, sometimes we already know the diagnosis and what treatment we should use–we just have to prove it to get the treatment covered. It’s ridiculous, but I don’t make the rules.
  6. Just to give us an answer. Sometimes, it’s just nice to have an answer. Even if there’s nothing we can do about it. And even if it won’t change a darn thing. We’re all human, and sometimes we just want to know why. And as long as the test doesn’t carry a high level of risk, it’s a perfectly good reason.

In a future post, I’ll discuss allergy testing specifically–when it’s actually useful, and why the results might not matter. But no matter what we’re testing for, the most important question to ask is, “What difference will the answer make?” The next important question is whether that difference is worth the cost, pain, and risk of the procedure required to perform the test. The fact that a test exists doesn’t mean we should order it. Fortunately, as a parent, your job isn’t to decide what tests are necessary–it’s to find a doctor you trust to help you make informed decisions about your child’s health. And that’s one of the most important decisions you’ll make.

As always, your comments are welcomed (even if you happen to disagree). I'll get back to you as soon as I can. Please try to keep it civil--I reserve the right to delete comments that are offensive or off-topic.

One thought on “Lab tests aren’t always helpful–here’s why:

  1. But sometimes parents are just blown off. I had been told that my daughter just had allergies, that’s why her eyes were red, she had a virus, that’s what caused the little red dots, she was growing, that’s why she was tired. Hey bruising was from playing. They finally ran a CBC to shut me up. It was read as normal until the lab called to confirm that her platelets were 26,000! She was finally dx with chronic ITP. She was possibly in danger for months, and also needless discomfort. So I say, run the tests, that’s what insurance is for.

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