Assessment of Renal Function from Plasma Creatinine in Adult Patients

Abstract

The diagnostic value of four different delimitations of plasma creatinine concentrations to assess whether—and to what extent—the combined function of the two kidneys is affected by disease was evaluated from simultaneous determination of plasma creatinine and glomerular filtration rate (GFR) in 380 adult patients (200 females and 180 males aged 20-79 years) and from the prevalence of four different degrees of relative renal function in a consecutive series of 578 patients with different nephro-urological disorders. The four degrees of relative renal function (with the delimitations expressed as per cent of corresponding age- and sex-dependent normal mean GFR) were as follows: normal (>75%); moderately decreased (75-52%); considerably decreased (51-28%); and severely decreased (<28%). The corresponding delimitations of plasma creatinine concentrations (μmol/l) into normal, moderately increased, considerably increased and severely increased were: <115; 115-150; 151-250; and >250 in females, and <128; 128-170; 171-270; and >270 in males. About 60% of the patients with moderately decreased relative renal function had a normal plasma creatinine, i.e. 60% of patients with moderately decreased relative renal function are overlooked when plasma creatinine is used for assessing relative renal function. In a patient with a plasma creatinine concentration which is normal, moderately increased, considerably increased or severely increased the probability to have the corresponding degree of relative renal function (normal, moderately decreased, considerably decreased, severely decreased) was found to be 0.80, 0.49, 0.67 and 0.99, respectively. A comparison between GFR (ml/min) and plasma creatinine in the 200 females and 180 males of various ages revealed the necessity to consider both sex and age in an estimation of GFR in absolute terms (ml/min) from plasma creatinine. When body weight also is taken into consideration it was found that GFR can be estimated in the individual patient with a reliability of ±20-25%. It is concluded that plasma creatinine is a reliable parameter to assess relative renal function at plasma creatinine values higher than 150 μmol/l in females and 170 μmol/l in males, and that estimation of GFR in absolute terms (ml/min) from plasma creatinine (considering sex, age, and body size) is suitable for dose calculations of potentially toxic drugs excreted via the kidneys.