By Cesar M Limjoco, MD
CMO, T- Medicus LLC
One of the kidneys’ main functions is clearing out the body’s waste products. Dysfunction first manifests as insufficiency in clearing out the body’s waste products. Insufficiency becomes failure when parenchymal (renal tissue) injury occurs. A major indicator of renal dysfunction is the increasing concentration of creatinine in the bloodstream.
Clinical studies have shown when serum creatinine rises to 1.5 times its baseline value (or ≥ 0.3 mg above baseline), kidney injury has occurred. Caveat: in small rises of creatinine caused by hypovolemia, hemoconcentration mimics a creatinine bump. Although creatinine has not increased, the fluid deficiency makes it look like there are increased levels. This is a false bump and not indicative of Acute Kidney Injury (AKI).
Studies have shown that with volume replacement in the preceding scenario, creatinine values return to normal within 6 hours and no injury to the kidneys has occurred. But, true acute kidney injury in the same scenario can happen and it becomes evident when volume replacement is not able to correct the creatinine bump in 6 hours. Damage to the renal parenchyma is said to have occurred at that point.
In Chronic Kidney Disease (CKD), the baseline creatinine is already elevated and continues to rise. Small rises, like 0.3 mg, may only indicate expected fluctuations in the CKD process. The 1.5X baseline would be a truer indicator of an acute injury on top of the CKD (AKI over CKD).
Thus, baseline creatinine is critical in ascertaining kidney disease. But, many times, the baseline creatinine is not available. One can ascertain the baseline level once the insult to the kidney has been corrected.
Be careful in interpreting abnormal laboratory values. As William Bruce Cameron once said, “Not everything that can be counted counts. Not everything that counts can be counted.”