Interpretation

Because serum creatinine is inversely correlated with glomerular filtration rate (GFR), when kidney function is near normal, absolute changes in serum creatinine reflect larger changes than do similar absolute changes when kidney function is poor. For example, an increase in serum creatinine from 1 to 2 mg/dL may indicate a decrease in GFR of 50 mL/min (from 100 to 50 mL/min), whereas an increase in serum creatinine level from 4 to 5 mg/dL may indicate a decrease of only 5 mL/min (from 25 to 20 mL/min).

Because of the imprecision of serum creatinine as an assessment of GFR, there may be clinical situations where a more accurate GFR assessment must be performed, iothalamate or inulin clearance are superior to serum creatinine and eGFR.

Several factors may influence serum creatinine independent of changes in GFR. For instance, creatinine generation is dependent upon muscle mass. Thus, young, muscular male patients may have significantly higher serum creatinine levels than older adult female patients, despite having similar GFRs. Also, because some renal clearance of creatinine is due to tubular secretion, drugs that inhibit this secretory component (eg, cimetidine and trimethoprim) may cause small increases in serum creatinine without an actual decrease in GFR.

According to the Kidney Disease: Improving Global Outcomes (KDIGO) CKD work group, chronic kidney disease (CKD) is defined as the abnormalities of kidney structure or function, present for more than 3 months, with implications for health.(3) CKD should be classified by cause, GFR category, and albuminuria category.(3)

Table. KDIGO guidelines provide the following GFR categories(2,3):

*In the absence of evidence of kidney damage, neither G1 nor G2 fulfill criteria for CKD.