This measurement method improves diagnosis of kidney problems in elderly

How the kidney function is estimated

Someone suffers from chronic kidney damage when the kidney function is less than 60%. If the kidney function is less than 60%, there is a greater risk of dialysis or death. There is debate whether this is also an appropriate threshold for elderly patients. In fact, previous studies suggested that with elderly, there may not be an increased risk of dialysis or death until kidney function is below 45%. This could mean that elderly patients with kidney function above 45% do not have an increased risk. But the 45% could also be due to estimates based on blood creatinine concentration, which may be less reliable for elderly.

Creatinine is a breakdown product of muscle mass. When the concentration of creatinine in the blood is low, the kidney function is estimated to be high. This is because the substance is rapidly eliminated by properly functioning kidneys. However, in elderly people with low muscle mass, an estimate of kidney function based on creatinine may be too high. The creatinine concentration in the blood is then low because of less muscle mass. And not because the substance is removed quickly by properly functioning kidneys. Dr. Fu investigated whether this is indeed the case and whether another measurement method is more reliable, a combination of creatinine and cystatin C.

Combination measurement more reliable

If both creatinine and cystatin C are used to estimate kidney function, there is an increased risk of dialysis and death even at a kidney function of 60%. With this, the study shows that the limit of kidney function of 60% is also appropriate for elderly to determine chronic kidney injury. In addition, the researchers show that the combination of creatinine and cystatin C leads to lower kidney function estimates. As a result, more elderly patients would be diagnosed with chronic kidney disease and qualify for treatment. In addition, the study shows that chronic kidney disease increases the risk of many more outcomes than previously thought, including infections and hospitalizations.

What does this mean for the elderly patient?

The outcomes of the study allow for better treatment decisions based on kidney function. For instance, by using the combined measurement, doctors could better determine when to start or stop certain medications or whether referral to a nephrologist, a specialist in kidneys, is necessary. On average, older patients will be more eligible for treatments that can delay kidney damage.  

Read the publication of this study in Annals of Internal Medicine here.