Inorganic sulfate is involved in metabolic processes of activation and detoxification of endogenous and exogenous compounds It plasma levels are maintained fairly constant (0.2-0.6 mM/L). Sulfate is excreted mainly by the kidney, via free glomerular filtration, followed by proximal tubular reabsorption with a saturable mechanism. Sulfate retention as a consequence of CKD has long been known. However, no studies have been done in adults to evaluate the relationship with GFR.
Sixty four adult CKD patients (30 males, age 25-85 years, serum creatinine 0.51-6.65 mg/dL). GFR was measured as the renal clearance of 99mTc-DTPA. Plasma creatinine was measured with a standard method, plasma sulfate levels with a turbidimetric method.
Plasma sulfate ranged 0.5-2.32 mM/L (mean 0.94) in men and 0.33-2.03 mM/L (mean 0.84) in women. With decreasing GFR sulfate rose exponentially to a maximum of 2.32 mM/L ( GFR 6.3 mL/min 1.73 m2). A significant correlation was found between plasma sulfate and creatinine (r=0.674). A significant correlations(r=0.651) was also found with GFR. The correlation was closer among men (r=0.70) then women (r=0.58). This finding could be due to a different tubular handling of sulfate related to sex: due to a larger number of tubular transporters, women have higher tubular reabsorption of sulfate which is saturated at higher plasma levels. The correlation of serum creatinine with GFR (r=0.874) was significantly closer than that of plasma sulfate with GFR (Figure).
Plasma sulfate correlates with GFR. Other factors affect this relationship: saturable tubular reabsorption and possibly tubular secretion of sulfate, together with the amount of dietary sulfate. In any case, plasma levels of sulfate should be taken into account in CKD patients, due to their relevance in acid/base equilibrium and detoxication mechanisms.
Correlation of serum creatinine and plasma sulfate with measured GFR.