What Do Abnormal Lab Results Mean?

Medical laboratory tests are an important part of diagnosing and treating many conditions. In psychiatry, for example, we often need to measure the metabolic effects of certain medications, monitor the blood concentration of lithium, or evaluate the relationship between thyroid hormone levels and depression.

When reviewing results, we ask: what do abnormal lab results mean in the context of this patient’s overall health? A “normal” result means the measured value falls within a reference range—above the lower limit and below the upper limit. An “abnormal” result occurs when values fall outside of that range, either too high or too low.

For instance, with a TSH test (Thyroid Stimulating Hormone), an abnormal result might be communicated as: “Your thyroid levels are too low,” “Your thyroid levels are normal,” or “Your thyroid levels are too high.”

However, with respect to any given test, this is inaccurate for as many as 5% of people—one person out twenty, often with significant clinical implications. This is because reference ranges are not absolute boundaries but statistical ones based not a black and white definition of “abnormal” but on a “distribution” of clinically normal and abnormal values. 

What is a Distribution?

In statistics, a distribution portrays the frequency of various outcomes within a data set. It is basically just a list of different values, in order, along with the number of times each value occurs, like this:

This might represent an experiment where 46 people without X-related disease had their blood drawn and the level for a protein called Y is measured. People must have a certain amount of Y to be healthy. If they have too little they develop “hypoX” and if too much, “hyperX.” A real world example of this would be thyroid hormone levels in people.

In the above graph, we see that :

• the most common value of the marker in healthy people is 50.0 with 14 of 55 people having that value (25%). 
• 40.0 and 60.0 are common as well—amounting to 36% of the test population. 
• We observe, then, that 25% + 36% of the test population = 61% have X values between 40% and 60% inclusive.
• 30.0 and 70.0 amount to another 15% of the test population, so that 25% + 36% +15%= 76% of the test population have values between 30% and 70% inclusive.
• 7 people have values 20.0 or 80 (13%) so that 89% of the values lie between 20% and 80% inclusive.
• Finally 3 people have values 10.0 or 90.0 (5%) so that 95% of the population have values that lie between 10.0 and 90.0 inclusive and this defines “normal” because “normal” is certain kind of bell-shaped distribution of values.

We now perform a second test on people all of whom have hypoX and a third test on people with hyperX. We find similarly roughly bell-shaped distributions in these tests as well. 

In the end, we discover from these the statistical range of values typically found in people who have no X-related illness, people with hypo-X and people with hyper-X. 

The way statistics define matters (the definition is a matter of choice, it isn’t found “in nature” as it were)  “in a group of normal people without X, 95% of them have values between 10.0 and 90.0,” which we call the reference range.

However, in above chart look at the value 100.0. There are 2 people (4%) who have no X-related illness but they have values that are very high and that fall within the typical range for people with hyper-x. In fact for every laboratory value, because of how the reference range is defined, for any condition X:

• There will be a small number of healthy people—5% or one out of twenty—with lab values that are defined as indicating disease
• There will be a small number of ill people—5% or one out of twenty—with lab values that are defined as indicating no disease
• 5% or one out every twenty laboratory  values are expected to be abnormal just by chance.

For laboratory values in a healthy population, these measurements typically form what is known as a “normal distribution” or “bell curve.” A smooth curve arises when the number of healthy individuals tested run into the hundreds or thousands. This curve shows that most values cluster around the average or median, while fewer values fall towards the outer “tails”.

What Do Abnormal Lab Results Mean?: Key Points

Individual Variability: Some healthy people fall outside a reference range due to age, sex, race, diet, exercise habits, and genetic dispositions.

Context is Crucial: Simply because a lab value falls outside the reference range doesn’t necessarily mean sickness. Similarly, values within the range don’t guarantee health. Laboratory values must be interpreted in a context  that includes symptoms, signs, history, other diagnostic information and an understanding that the laboratory value boundaries are clinically fuzzy.

Customized Care: Treatment and monitoring must be tailored to each individual’s unique baseline, rather than to the generalized reference range.

In summary, medical lab test reference ranges are guides and not outright indicators of either health or disease. They are statistical tools that, while invaluable, require interpretation within the broader context of an individual’s overall condition and circumstances. 

Understanding Your Next Steps

It’s natural to feel uncertain when you receive unexpected test results, and many people wonder, “what do abnormal lab results mean?” The truth is, these results don’t always point to a serious condition—they may reflect temporary changes, testing variations, or factors that require further evaluation. What matters most is working with a qualified professional who can interpret your results in the context of your overall health.

At the Sterling Institute in Danbury, Connecticut, our team of experienced psychiatrists and clinicians is here to help patients make sense of complex health information and guide them toward the right next steps. We also provide telehealth services in New York and Florida, making expert care accessible wherever you are.