Climate Factors May Influence Glomerular Filtration Rate in Nephrology Patients.

INTRODUCTION: Approximately 37 million U.S. adults have chronic kidney disease (CKD), characterized by reduced glomerular filtration rate (GFR). Previous work has shown GFR to be sensitive to certain environmental features, such as heightened temperature and pollution. Other components of climate merit investigation.

PURPOSE: To examine the effects of temperature, air pressure, and humidity on GFR.

METHODS: We evaluated 322 nephrology patients who were consecutively admitted to a single hospital between January 2017 and July 2018. At intake, patients were assessed for demographic, anthropometric, and cardiometabolic parameters, and a detailed medical history was collected. The exact ambient temperature, air pressure, and humidity was documented for each patient corresponding to their time of admission. We characterized the study sample with basic descriptive statistics. Linear regression tested the effect of climate variables on GFR holding all significant confounders constant.

RESULTS: Patients were 65.8 ± 17.0 years old, 50.9% were male, 42.3% were obese, 12.3% reported smoking, 21.9% reported drinking, 16.8% had a diagnosis of cancer, 48.1% had diabetes, 26.1% had coronary artery disease, 1.9% had hepatitis, 6.5% had end-stage renal disease, 3.4% had a kidney transplant, and 8.4% had used dialysis (either currently or in the past). Systolic blood pressure was 134.5 ± 37.2 mmHg, diastolic pressure was 72.8 ± 18.4 mmHg, hemoglobin was 11.6 ± 2.6 g/dL, creatinine was 2.8 ± 1.5 mg/L, and GFR was 26.5 ± 12.3 mL/min. GFR was correlated with humidity (p=0.029) but not temperature (p=0.170) or air pressure (p=0.404). Linear regression found each additional percentage point of humidity at the time of intake to correspond to a reduction in GFR of 7.6 mL/min (p=0.018; 95% CI: -1.314 to -13.899) holding all significant confounders constant: sex (p=0.027), diastolic blood pressure (p=0.033), hemoglobin (p<0.001), diagnosis of cancer (p=0.001), diagnosis of coronary artery disease (p=0.028), diagnosis of peripheral vascular disease (p=0.041), diagnosis of hepatitis (p=0.020), hyperglycemia (p=0.001), current alcohol intoxication (p=0.023), and use of dialysis (p<0.001). The overall model was significant (p<0.001; r2 =0.317). Using all of the same predictors, but holding constant CKD stage (p<0.001), humidity remained significant (β = -6.837; p=0.029; 95% CI: -0.703 to -12.970). Temperature and air pressure were insignificant in both models (p>0.500); humidity remained significant (p<0.025) when controlling for them. All other potential confounders were tested; none were significant (p>0.100) and all combinations of inclusion in the model preserved the significance (p<0.025) and magnitude (β < -7.000) of humidity.

CONCLUSIONS: Ambient humidity demonstrated a robust and resilient effect on kidney function. Higher humidity corresponded to a reduction in estimated GFR across all stages of CKD and within stages. Other climate factors exhibited no effect. A possible mechanism is the decrease in evaporative cooling leading to additional sweat loss, reduced plasma volume, and a lower blood pressure gradient in the glomerulus.