Ambient Temperature an Under-Appreciated Source of Lab-Test Variation

By Reuters Staff

December 13, 2021

NEW YORK (Reuters Health) - Ambient temperature on the day of a blood draw may impact the results of many widely used laboratory tests, which could influence decisions on whether to prescribe medications.

"Whatever their cause, temperature produces undesirable variability in at least some tests, which in turn leads to distortions in important medical decisions," Dr. Devin Pope of the University of Chicago said in a news release.

With data from more than 4.8 million people spanning seven years, Dr. Pope and Dr. Ziad Obermeyer of the University of California, Berkeley, modeled 215 million laboratory-test results from several climate zones, controlling for individual patient and city-week fixed effects.

"This measures how day-to-day temperature fluctuations affect results, over and above the patient's mean values, and seasonal variation," they explain in the journal Med.

They found that temperature affected more than 90% of individual test results and 51 of 75 clinical assays, including measures of kidney function (increased creatinine, urea nitrogen and urine specific gravity), cellular blood components (decreased neutrophils, erythrocytes and platelets) and lipids (increased HDL-cholesterol, decreased total, cholesterol, triglycerides and LDL-C).

"It's important to note that these changes were small: less than one percent differences in most tests under normal temperature conditions," Dr. Obermeyer said in the release.

"These small, day-to-day fluctuations are unlikely to correlate with long-term physiological trends," the researchers note in their paper.

"For example, lipid panels checked on cooler days look lower risk, but these short-term changes probably do not reflect stable changes in cardiovascular risk," they point out.

Nonetheless, the data suggest that clinicians appear to treat these patients differently, writing 9.7% fewer statin prescriptions checked on the coolest versus the warmest days.

While the researchers could not pinpoint the exact underlying mechanisms for fluctuations in lab results associated with ambient temperature, possible explanations include blood volume, specific assay performance, specimen transport or changes in lab equipment.

The study had no specific funding.

SOURCE: Med, online December 10, 2021.