Seasonal variation in estimated glomerular filtration rate based on serum creatinine levels in hypertensive patients

Seasonal variations in blood pressures should be kept in mind when controlling blood pressure in hypertensive patients. Seasonal variations in glomerular filtration rate (GFR) also may have a clinical significance. However, it is time-consuming to measure GFR directly. We therefore examined the seasonal variation in estimated glomerular filtration rate (eGFR) based on serum creatinine levels in hypertensive patients without CKD (eGFR ≥ 60 mL/min/1.73 m(2)) and those with chronic kidney disease (CKD) (eGFR < 60 mL/min/1.73 m(2)). This study included 47 hypertensive patients without CKD (69 ± 11 yrs) and 55 hypertensive patients with CKD (76 ± 8 yrs). The eGFR was determined from the equation: eGFR = 194 × age(-0.287) × (serum creatinine)(-1.094) (× 0.739 if female). Overall, both groups of hypertensive patients demonstrated similar seasonal variations in eGFR. Importantly, hypertensive patients without CKD and those with CKD showed the lower eGFR in summer (June-August) (71.8 ± 13.2 and 37.2 ± 13.0 mL/min/1.73 m(2), respectively) compared with the eGFR in spring (March-May) (77.9 ± 13.0 and 43.0 ± 14.0 mL/min/1.73 m(2), respectively) (p < 0.05). The decrease in eGFR from spring to summer was similar for both types of hypertensive patients (without CKD, -6.1 ± 7.0; with CKD, -5.8 ± 5.2 mL/min/1.73 m(2)). However, the percent change in eGFR from spring to summer was greater in hypertensive patients with CKD (-13.8 ± 9.4 %) than in those without CKD (-7.7 ± 8.3 %) (p = 0.001). In conclusion, careful observation regarding renal function is needed for hypertensive patients with CKD during summer.