Measurement of Kidney Function

Why MEASURE Kidney Function?

1) Identification of possible kidney impairment / renal failure in your patient

2) Modification of dosages of drugs which are cleared by the kidneys

Which patients are at risk of developing Renal Failure?

Monitoring a Patient’s Kidney Function

Clinical Assessment for Kidney Function

Use of Bedside Clinical Data

Modern Imaging Technique

1) Include macroscopic views of renal blood flow, filtration and excretory function.

2) Some of these are used clinically but some can currently only be used experimentally in the lab.

What is RENOGRAPHY?

1) Gamma camera planar scintography

2) Positron emission tomography (PET)

2) Single photon emission computerised tomo-graphy (SPECT)

Biochemical Data

Useful for identifying kidney impairment and renal failure

Blood (plasma or serum) markers of renal function:

1) Plasma or serum creatinine (sCr)

2) Plasma or serum urea or blood urea nitrogen (BUN)

• Plasma = serum + clotting proteins (e.g. fibrinogen)

What is PLASMA CREATININE?

What is Plasma Creatinine INCREASED by?

What is Plasma Creatinine DECREASED by?

What are the different RANGES of Plasma Creatinine?

What is PLASMA UREA?

What is Plasma Urea INCREASED by?

What is Plasma Urea DECREASED by?

What is RENAL CLEARANCE?

1) Clearance = the volume of plasma (mL) completely cleared of a given substance in unit time (min)

2) If we know the “renal clearance” of a substance which is

  - just filtered

  - not reabsorbed

  - not secreted

  then we can calculate Glomerular Filtration Rate (GFR) in mL/min

What are the ideal markers of GFR?

What is EXCRETION RATE?

1) The rate at which a substance is excreted via the kidney and is measured as mmol/min or mg/min

2) Similar to clearance which measures how quickly a substance is cleared from the blood while excretion rate measures how quickly it is being excreted.

Examples of Renal Clearance

How to CALCULATE Renal Clearance?

What is GLOMERULAR FILTRATION RATE (GFR)?

What is INULIN?

What are the DRAWBACKS of Inulin to measure GFR?

What is CREATININE CLEARANCE?

What are the ADVANTAGES of Creatinine Clearance?

1) Cheap, easy, reliable, used widely clinically

2) Creatinine is endogenous - produced from muscle by creatinine phosphate

3) Avoids IV infusion, just requires venous blood and urine samples

4) Usually measured over a 24-hour period to get reliable results with samples taken before breakfast

5) Must remember to take into account patient features which may affect levels, e.g. if person has muscle disease/damage or has had large quantities of meat to eat

How can CrCl be adjusted to BODY SURFACE AREA?

Estimation of GFR using Plasma Creatinine only

Classification of Renal Failure

How can PAH Clearance be used to measure Renal Blood Flow?

What are BIOMARKERS of Renal Disease?

1) Indicators of renal function such as plasma creatinine or BUN increase only after there is significant loss of renal function

2) Typically, there is a 60% loss in renal function before plasma creatinine or BUN increases

3) Urinary protein excretion can also be used as an indicator of chronic kidney disease / diabetic kidney disease but also later diagnosis

What are the EXAMPLES of Biomarkers of Renal Disease?

Summary