Ambient temperature influences many common lab tests, and these distortions likely affect medical decision making, such as whether to prescribe medications, according to new research published in the journal Med.
To account for this, the researchers suggest that laboratories could statistically adjust for ambient temperature on test days when reporting lab results.
“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 of the University of California, Berkeley. “This is exactly the kind of pattern that doctors might miss. We’re not looking for it, and lab tests are noisy.”
Delving into this problem, Obermeyer and Devin Pope of the University of Chicago analysed a large dataset of test results from different climates. In a sample of more than four million patients, they modelled more than two million test results based on temperature. They measured how day-to-day temperature fluctuations influenced results, over and above the patients’ average values, and seasonal variation.
Temperature was found to affect more than 90% of individual tests and 51 of 75 assays, including measures of 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 small fluctuations did not likely reflect long-term physiological trends. For example, lipid panels checked on cooler days appeared to suggest a lower cardiovascular risk, resulting in almost 10% fewer prescriptions for cholesterol-lowering drugs called statins to patients tested on the coolest days compared to the warmest days, despite the results likely not reflecting stable changes in cardiovascular risk.
Since the study wasn’t an experiment, the exact mechanisms underlying the fluctuations in lab results could not be pinpointed. However, blood volume, specific assay performance, specimen transport, or changes in lab equipment might explain them. “Whatever their cause, temperature produces undesirable variability in at least some tests, which in turn leads to distortions in important medical decisions,” Pope said.
Laboratories could get around this by statistically adjusting for ambient temperature on the test day when reporting lab results. This could be a way to reduce weather-related variability without expensive temperature control equipment.
In practice, decisions on adjustment would need to be at the discretion of the laboratory staff and the treating physician, potentially on a case-by-case basis.
According to the authors, the study may also have broader clinical implications. “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,” Obermeyer said. “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.”
Source: Science Daily
