Measure of Kidney Function

Question 1

In relation to kidney function, what does serum creatinine measure?

Answer 1

Byproduct of muscle metabolism excreted by kidneys

Question 2

What trait/s might alter serum creatinine levels and how?

Answer 2

Serum creatinine decreases with:
- age
- muscle mass (unless counteracted with weight-lifting or resistance training)

Question 3

What serum creatinine levels would be expected in patients with abnormal kidney function and low muscle mass? Normal muscle mass? Why?

Answer 3

With abnormal kidney function, kidneys can’t excrete creatinine. So…

Low muscle mass => possibly normal serum creatinine

Normal muscle mass => possibly elevated serum creatinine

Question 4

What serum creatinine levels would be expected in patients with normal kidney function and low muscle mass? Normal muscle mass? High muscle mass?

Answer 4

If normal renal function:

Low muscle mass => decreased serum creatinine

Normal muscle mass => normal serum creatinine

High muscle mass => elevated serum creatinine

Question 5

Compare serum creatinine and creatinine clearance as measures of kidney function.

Answer 5

Creatinine clearance (CrCl; mL/min) = better measure than serum creatinine

24-hour urine collection = most accurate but is very inconvenient

Question 6

What convenient measure of kidney function can be used as a proxy for creatinine clearance?

Answer 6

Estimated Glomerular Filtration Rate (eGFR)

Question 7

What is a normal eGFR?

Answer 7

Normal > 60 mL/min/1.73 m2

Abnormal < 60 mL/min/1.73 m2

Question 8

What common condition can result in a low eGFR, especially among the elderly?

Answer 8

Dehydration

*** Dehydration = #1 cause of decreased eGFR in elderly

*** @ 38% of patients =/> 70 years w/o HTN or DM have eGFR < 60