A clinical appraisal of the plasma concentration and endogenous clearance of creatinine

The normal values for the plasma concentration, excretion and twenty-four hour endogenous clearance of creatinine are given. Thirty men and thirty women were studied and in fifteen of each sex, measurements of both creatinine and true creatinine in the plasma were made. The non-creatinine chromogen did not influence the variability of the plasma values within a single individual or among a group of individuals. Correlation analyses revealed that the sex difference in plasma concentration and clearance could be removed by correcting for lean body weight. In ten additional subjects, there was no difference in one hour clearance values measured in the morning and afternoon, but these values did exceed the twenty-four hour values by some 7 to 11 per cent. In eighty patients with evidence of renal disease, it was found that if the plasma creatinine was less than 1.25 mg. 100 ml . in men and less than 1.1 mg. 100 ml . in women, the clearance value is normal unless the patient has extensive muscular wasting. If the plasma concentration is 1.25 to 1.75 mg. 100 ml . in men or 1.1 to 1.4 mg. 100 ml . in women, the clearance may vary from definitely low to normal values. With values greater than 1. 1.75 mg. 100 ml . in men and 1.4 mg. 100 ml . in women, the clearance is always low. Comparable relationships exist with true creatinine measurements. It is concluded that clearance measurements should be made and reliance not placed on the value predicted from the concentration of true creatinine in the plasma. The variability of the values in patients with evidence of renal disease was no greater for creatinine than for true creatinine measurements, and the information provided with each method was in close agreement. Either method is suitable for clinical purposes but a preference is expressed for true creatinine measurements if the plasma values are low normal or less. It is concluded that restrictive measures designed to minimize the variability resulting from changes in diet and the amount of physical activity are not justified. Similarly, corrections for surface area and lean body weight improve the normal values but are of limited usefulness in patients with evidence of renal disease. Creatinine formation in the body is briefly reviewed and instances of diminished production are commented on. Although clearance measurements offer the best means of detecting definite impairment of renal excretory function, the wide range of normal values limits the usefulness of suc