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Renal Function by Serum Markers

Renal Function by Serum Markers
Serum creatinine (Ccr). Serum creatinine is most commonly used clinical test for renal function. The normal value is 1 milligram percent. However, it depended on age and the muscle mass. In the older people, creatinine production is decreased due to reduced muscle mass. And glomerular filtration capacity is also decreased as a part of aging process. And because the parallel decrease in creatinine production. And a filtration capacity that result in a relatively normal serum creatinine. Therefore, serum creatinine is not a reliable measure for kidney function in the elderly. The serum creatinine is also not a reliable estimate for unstabilized renal function.
In glomerular nephritis when kidney function begins to deteriorate, it takes time for serum creatinine to rise up to a new higher steady-state. On the other hand, for example after kidney transplantation where renal function begins to improve, it also takes time for serum creatinine to decline to a new lower steady state. So in such case creatinine clearance is a better indicator for change of renal function than serum creatinine. And here I have one example. We have an acute urinary tract obstruction case. And when that happens, the serum creatinine shut up to 7 milligram percent. And the BUN rise up to 63 or 65 percent.
After the surgery, it takes 48 hours for the serum creatinine to reduce to the normal level of 1.3 or nearly 1 normal level. And it also takes 40 hours for BUN to decline to 26 normal value. And so that we can see that serum creatinine or BUN is not a good indicator for renal function when the function is unstable. Another serum marker. Blood Urea Nitrogen , or BUN. The normal value is 7 to 21 milligram percent. However, it is subject to dietary effect, particularly protein foods. And that’s why we use BUN to serum creatinine ratio instead of BUN by itself. Serum Cystatin-C. Serum Cystatin-C is a tissue protein with a molecular weight about 13,000.
It is an enzyme produced at a constant rate by blood cells. And it is filtered by the glomerulus. Unlike serum creatinine, it is less dependent on age, gender, race or lean muscle mass. Therefore, the change of serum cystatin-c is with reflective of progressive changes of renal function. And the normal value interestingly is also one milligram per liter. And this is approved or has been approved by the FDA for diagnostic use.

In this step, Prof. Lee explains three serum markers, including serum creatinine (Ccr), blood urea nitrogen (BUN), and serum cystatin-C.

When we use serum creatinine as a marker, we should notice that it is not a reliable indicator for the elderly and those who have unstable renal function. Instead, creatinine clearance is a better indicator for change of renal function.

Besides, Prof. Lee demonstrates the return of Ccr and BUN to normal values in a patient with acute urinary tract obstruction.

For BUN, its normal value is between 7 and 21 mg/dL in the US. However, it is subject to dietary effect, especially in protein foods. Therefore, we can use BUN/ Ccr ratio to avoid this situation.

Ultimately, we can see that serum cystatin-C is a kind of tissue protein, which is less dependent on age, gender, race or lean muscle mass.

If you have any questions about the serum markers, please leave them below.

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Pharmacokinetics: Drug Dosing in Renal Disease

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