Kidney tests that must be done if you suffer from renal disorders



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Kidney tests to be done if your suffering from renal diseases

Nephrology is the study of kidneys. Many people suffer from various kidney diseases. Most kidney tests are prescribed by the doctors. But we must have a basic knowledge about it.

In this article, i will talk about kidney disease tests that must be done.


L FUNCTION TESTS

URINE ANALYSIS:

i) Physical examination (output, colour, specific gravity, pH, osmolality)

ii) Chemical constituents (protein, glucose, red cells, haemoglobin)

iii) Bacteriologic examination

iv) Microscopy

2. CONCENTRATION AND DILUTION TESTS:

i) Concentration test (fluid deprivation test)

ii) Dilution test (excess fluid intake test)

3. BLOOD CHEMISTRY:

 Urea : 25 to 40 mg/dL

 Uric acid : 2.5 mg/dL

 Creatinine : 0.5 to 1.5 mg/dL

 Blood urea nitrogen (BUN)

4. RENAL CLEARANCE TEST:

ii) Creatinine clearance

iii) Urea clearance

Serum Creatinine

 Creatinine is a waste product that comes from the normal wear and tear on muscles of 

the body. 

 Creatinine levels in the blood can vary depending on age, race and body size. 

 Creatinine is freely filtered at the glomerulus and is also to a very small extent 

secreted into the tubules. So any problem with glomerular filtrations has a significant 

effect on the excretion of creatinine resulting in a much substantial rise in serum 

creatinine level.

 Normal serum creatinine level is 0.6 to 1.5 mg/dl. Serum creatinine is a better 

indicator of renal function and more specifically glomerular function than urea.

 A creatinine level of greater than 1.2 for women and greater than 1.4 for men may be 

an early sign that the kidneys are not working properly.

 As kidney disease progresses, the level of creatinine in the blood rises.

serum urea

Serum/plasma urea concentration reflects the balance between urea production in 

the liver and urea elimination by the kidneys, in urine; so increased plasma/serum urea can 

be caused by increased urea production, decreased urea elimination, or a combination of the 

two.

Blood urea nitrogen (BUN)

Sometimes the Serum urea level is expressed as blood urea nitrogen. BUN can be 

easily calculated from the serum urea level. The molecular weight of urea is 60 and it 

contains two nitrogen atoms of combined atomic weight of 28. Hence the contribution of 

nitrogen to the total weight of urea in serum is 28/60 that is equal to 0.47. Hence the serum 

urea levels can be easily converted to BUN by multiplying it by 0.47. A rise in blood nitrogen 

level is known as azotemia.

Creatinine Clearance

 Creatinine is filtered at the glomerulus and its reabsorption at the tubular level is 

insignificant. Because of this creatinine clearance can be used to measure Glomerular 

Filtration Rate (GFR).

 It is measured over a period of 24 hrs. 

 For this urine is collected over a 24 hour period and blood samples are also collected. 

 The concentration of creatinine is measured both in the urine as well as the serum 

sample. Creatinine clearance is measured by the following method: 

 Creatinine is freely filtered at the glomerulus and is also to a very small extent 

secreted into the tubules. So any problem with glomerular filtrations has a significant 

effect on the excretion of creatinine resulting in a much substantial rise in serum 

creatinine level.

Creatinine is used to measure GFR accurately. It is easier than inulin clearance, because, 

creatinine is already present in body fluids and its plasma concentration is steady throughout 

the day. It is completely filtered and being a metabolite it is neither reabsorbed nor secreted.


UREA

Urea is naturally produced when the liver breaks down protein or amino acids, and 

ammonia. The kidneys then transfer the urea from the blood to the urine.

Urea is produced in the liver and is a metabolite (breakdown product) of amino acids. 

Ammonium ions are formed in the breakdown of amino acids. Some are used in the 

biosynthesis of nitrogen compounds. Excess ammonium ions are converted to urea.

Ammonia is highly toxic in the body and therefore cannot be allowed to accumulate. With the 

help of specific catalysts in the liver cells carbon dioxide reacts chemically with the ammonia 

molecule, NH3. The less toxic nitrogenous compound urea is produced together with water.

CO2 + 2NH3 (NH2)2CO + H2O

This series of reactions is called the ornithine cycle. The urea and water are released from 

the liver cells to the bloodstream and transported to the kidneys where the blood is filtered 

and the urea is passed out of the body in the urine. Urea is very soluble and a small molecule, 

so it is relatively easily passed out by the kidneys as a solution in water.

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