Biochemistry: Determination of Serum Creatinine

Questions and Answers

What is the wavelength range used in the assay principle of creatinine measurement?

380-420 nm

620-650 nm

550-580 nm

480-520 nm (correct)

What is the temperature range for the assay conditions?

30-35°C

20-25°C (correct)

25-30°C

15-20°C

What is the purpose of reading the initial absorbance (A1) in the assay?

To calculate the rate of reaction

To measure the concentration of creatinine

To set a baseline for the reaction (correct)

To measure the concentration of protein

What is the normal range of creatinine levels in males?

0.6-1.4 mg/dl Signup and view all the answers

What can cause creatinine levels higher than normal levels?

All of the above Signup and view all the answers

What is the minimum loss of renal function required to increase serum creatinine from 1.0 to 2.0 mg/dL?

50% loss of renal function Signup and view all the answers

How do creatinine levels compare to blood urea nitrogen (BUN) levels in response to kidney problems?

Creatinine levels increase more slowly than BUN levels Signup and view all the answers

Why do creatinine concentrations tend to be higher in men than in women and children?

Due to differences in muscle mass Signup and view all the answers

Study Notes

Creatine and Creatinine

Creatine is synthesized in the liver, pancreas, and kidneys from the amino acids arginine, glycine, and methionine.
Creatine is transported through the circulatory system to muscle where it is converted to phosphocreatine and acts as an energy reservoir.
Creatinine is a waste product produced in muscles from the breakdown of creatine through hydrolysis.

Importance of Serum Creatinine Measurement

Determining serum creatinine levels helps assess kidney function.
Serum creatinine is a more specific and sensitive indicator of renal disease than Blood Urea Nitrogen (BUN).

Why Serum Creatinine is a Better Indicator than BUN

Production of creatinine depends on an individual's muscle mass, which usually fluctuates very little with normal kidney function.
As a result, the amount of creatinine in the blood remains relatively constant and normal.
Creatinine is affected very little by liver function, making an elevated blood creatinine a more sensitive indication of impaired kidney function than BUN.

Disadvantages of Serum Creatinine

Serum creatinine is very insensitive to even substantial declines in glomerular filtration rate.
Glomerular filtration rate may be reduced by up to 50% before serum creatinine becomes elevated.

Sample Collection and Stability

Serum or plasma samples are required for creatinine measurement.
The only acceptable anticoagulants are heparin and EDTA.
Creatinine in serum is stable for 24 hours at refrigerated temperatures (2 - 8°C) and several months when frozen (-20° C).
Spot urine or 24-hour urine sample collection is needed for the measurement of urine creatinine.

Assay Principle and Procedure

The Jaffé technique, described in 1886, is still the most widely used method for measuring creatinine in biological fluids.
Creatinine in alkaline solution forms a yellow-red complex with alkaline picrate.
The assay procedure involves mixing and reading absorbance at specific wavelengths and temperatures.

Normal Range and Variables

Normal creatinine levels:
- Male: 0.6–1.4 mg/dl
- Female: 0.6–1.2 mg/dl
Creatinine concentrations are slightly higher in men than in women and children due to muscle mass.
Creatinine levels higher than normal may be due to prerenal causes (e.g., heart disease, dehydration), muscle disease (e.g., acromegaly), or renal causes (e.g., impaired kidney function).

Description

This quiz covers the synthesis, transport, and function of creatine in the human body, specifically its role in muscle energy reservoirs. It also discusses the determination of serum creatinine, an important clinical test.