Temperature influenced almost 90% of individual tests and 51 of 75 assays, including kidney function, cellular blood components, and lipids like cholesterol and triglycerides.
Ambient temperature affects the outcomes of several of the most often used laboratory tests, and these distortions are likely to affect medical decision making, such as whether to prescribe drugs, researchers report in the journal Med.
According to the authors, when reporting lab results, laboratories could statistically adjust for ambient temperature on test days to account for day-to-day variations.
“When a doctor orders a laboratory test, she uses it to shed light on what’s going on inside your body, but we wondered if the results of those tests could also reflect something that’s going on outside of your body” said study co-author Ziad Obermeyer.
“This is exactly the kind of pattern that doctors might miss. We’re not looking for it, and lab tests are noisy.”
Obermeyer and Devin Pope of the University of Chicago investigated this question by analyzing a huge dataset of test results covering many climate zones from 2009 to 2015. They modeled over two million test findings as a function of temperature in a sample of over four million patients. They examined how day-to-day temperature changes, in addition to the patients’ average values and seasonal variance, influenced findings.
The temperature was found to influence more than 90% of individual tests and 51 of 75 assays, including kidney function, cellular blood components, and lipids such as cholesterol and triglycerides.
“It’s important to note that these changes were small: less than one percent differences in most tests under normal temperature conditions,” Obermeyer said.
These minor, day-to-day oscillations were unlikely to reflect long-term physiological trends. For example, lipid panels checked on cooler days appeared to indicate a lower cardiovascular risk, resulting in nearly 10% fewer prescriptions for cholesterol-lowering drugs known as statins to patients tested on cooler days compared to warmest days, even though these results most likely did not reflect stable changes in cardiovascular risk.
Since the study was not an experiment, the researchers were unable to identify the precise mechanisms causing the variations in lab outcomes. Blood volume, specific assay performance, specimen transport, or changes in lab equipment are all possible factors.
“Whatever their cause, temperature produces undesirable variability in at least some tests, which in turn leads to distortions in important medical decisions,” Pope added.
One operational implication of the study is that when reporting lab findings, laboratories could statistically correct for ambient temperature on the test day. This could reduce weather-related variability at a lesser cost than investing in new laboratory test technology or temperature control in transport vans. In practice, adjustment decisions would have to be made at the discretion of the laboratory staff and the treating physician, maybe on a case-by-case basis.
The findings, according to the authors, may have larger clinical consequences.
“The textbook way of thinking about medical research is bench to bedside. First, we come up with a hypothesis, based on theory, then we test it with data,” said Obermeyer.
“As more and more big data comes online, like the massive dataset of lab tests we used, we can flip that process on its head: discover fascinating new patterns and then use bench science to get to the bottom of it. I think this bedside-to-bench model is just as important as its better-known cousin because it can open up totally new questions in human physiology.”
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