Kidney function can be measured by the lab value- creatinine. Creatinine is a break down product of muscle, that is then filtered through the kidney. Everybody breaks down muscle on a daily basis, generating creatinine. The amount of creatinine that is generated when muscle breaks down is dependent on how much muscle an individual has. So, a person who may be 300 pounds of muscle will generate more creatinine on a daily basis when compared to a thin, frail patient, who has very little muscle. If more creatinine is generated, then the baseline creatinine measured in the blood will higher. If less creatinine is generated, then baseline creatinine will be lower. That is why the ‘normal’ creatinine noted in the labs has a wide range listed. Using this same line of reasoning, if less creatinine is filtered through the kidney due to impaired kidney function, then blood creatinine will rise. This is why the creatinine value is used as a measure of kidney function.
Labs also result a value called eGFR. The eGFR result is the conversion of the creatinine value to terms reflecting the filtering ability of the kidney; this is listed as milliliters/min of filtration. If this eGFR is an acute change compared to previous levels, then the kidney impairment is classified as acute kidney injury. If, however, this eGFR has been persistent for at least the prior 3 months, then the kidney impairment is classified as chronic kidney disease.
Chronic kidney disease is further broken down into stages: stage I (90-120 ml/min which represents normal function but there may be urine abnormalities such as protein in the urine,) stage II (60-90 ml/min,) stage IIIa (45-60 ml/min,) stage IIIb (30-45 ml/min,) stage IV (15-30ml/min,) and stage V (less than 15 ml/min.) Dialysis is usually indicated at stage V kidney disease. There are many varied causes of acute and chronic kidney disease, and evaluation by the nephrologist will help determine the cause. Sometimes a kidney biopsy may be necessary. Kidney disease is usually not reversible in most cases. Our goal is to try to determine the cause of kidney disease, and slow its progression to ultimately avoid the need for dialysis.