Skip to Main Content

++

Introduction

++

The kidney has a number of functions, including:

++

  • Maintenance of homeostasis.

  • Production of erythropoietin.

  • Maintenance of blood pressure.

  • Hydroxylation of vitamin D.

++

It is the investigation of the first of these with which this Chapter is concerned.

++

Creatinine as an indicator of renal function

++

One of the major roles of the kidney is the excretion of soluble waste. This is achieved by the process of glomerular filtration. Creatinine is commonly used as an indicator of the glomerular filtration rate (GFR). Creatinine is a non-toxic breakdown product of creatine, a short-term energy store found in muscle (in the form of phosphocreatine) (1.1).

++
1.1

Metabolism of phosphocreatine to creatinine.

Graphic Jump Location
++

Laboratory analysis of serum creatinine entails chromo-graphic analysis of the products of the Jaffe reaction. Creatinine is mixed with alkaline picramate and an orange coloured compound is formed (1.2). The product is then analysed by a colorimeter.

++
1.2

Creatinine after alkaline picramate reaction.

Graphic Jump Location
++

Table 1.1 shows possible causes for a raised creatinine.

++
Table Graphic Jump Location
Table 1.1Causes of a raised creatinine
++

The 'goulash effect' is a transient rise in serum creatinine after ingestion of large quantities of boiled meat.

++

Glomerular filtration rate

++

Measurement of serum creatinine has its limitations. The relationship between serum creatinine and GFR is not linear, and serum creatinine level may not rise significantly until GFR is as low as 30% of normal.

++

GFR is an important measurement that provides clinicians with information about overall renal function. GFR can be estimated in a number of ways.

++

Clearance concept

++

GFR can be estimated by measuring clearances of a substance in which filtration by the glomerulus equals excretion in the urine. Clearance is the volume of plasma that is completely cleared of a substance by the kidneys per unit time (1.3).

++
++

Calculation of creatinine clearance

++

Creatinine is an endogenous substance that is present at a relatively constant level (1.4). Measurements and calculation according to the formula in figure 1.3 require 24-hour collection of urine (1.5). Therefore, patients need to be compliant for results to be accurate.

++
1.4

Calculation of creatinine clearance (ml/min).

Graphic Jump Location

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.