By : Mohammed Sadiq

Urea
Urea (H2N–CO–NH2) is the diamide of carbonic acid ( have no charge ).
Unlike ammonia, it is neutral and therefore relatively non-toxic
( obtain proton → ammonium Ion ) ( it have a charge ).
Urea is the major excretory product of protein metabolism.
Note :- urea at high level Inhibit bone marrow and decrease RBC synthesis and causes
anemia

Urea
1- Urea is synthesized in the liver
2- transported through blood
3- excreted in urine

Urea excretion represents the major route for nitrogen excretion. So what else ?
Answer : some nitrogen may be excreted in the form of creatinine, also be excreted in the
form of ammonia and uric acid

Clinical Applications
Evaluating renal function
Renal function can be evaluated through various clinical tests and assessments. Common
methods for evaluating renal function include :
Glomerular Filtration Rate (GFR) : GFR is considered the best overall indicator of renal
function. It can be measured directly using exogenous filtration markers such as inulin
or iothalamate, or estimated using equations based on serum creatinine levels (eGFR).

Blood Urea Nitrogen (BUN) and Creatinine Levels : These are commonly measured in
blood tests to assess kidney function. Elevated levels may indicate impaired renal
function.

Urinalysis : Analysis of urine can provide important information about kidney function,
including the presence of protein, blood, glucose, and other substances.

Urine Albumin-to-Creatinine Ratio (ACR) : ACR is used to screen for kidney damage,
especially in individuals with risk factors for kidney disease such as diabetes or
hypertension.
 Imaging Studies : Imaging techniques such as ultrasound, CT scans, or MRIs can be
used to visualize the kidneys and urinary tract, identifying structural abnormalities or
obstructions.

Renal Biopsy : In certain cases, a renal biopsy may be performed to assess the cause
and severity of kidney disease.

Assessment of hydration status

Urea level effected highly by hydration state
Dehydration ↑, plasma ↓, urea ↑
hydration state ( normal ), plasma ( normal ), urea ( normal )
for person with shock, internal bleeding ( plasma level ↓, urea level ↑ )

Determination of nitrogen balance

[ + ev, nitrogen balance ] → recover from illness → [ blood urea ↓ ]

[ - ev, nitrogen balance ] → injury, sever injury, muscles lysis, muscles damage
→ [ blood urea ↑ ]

Verifying adequacy of dialysis

Dialysis : We artificially get rid of harmful substances or add useful substances

For patients with chronic renal disease, when they reach end stage of renal failure
Mean the kidney is no longer effective in filtration of harmful substance, so we need an
alternative way to get rid of these harmful substance ( we do dialysis )

We should avoid over dialysis ( because the membrane of the device is not really
selective, its depend on the different of concentration, so we will lose some beneficial
substance like water soluble vitamins and amino acid if we did over dialysis.

Normal blood urea level ( 15 – 45 mg /dl ), so patients with renal failure can reach
even ( 200 gm/dl ), make sure you stop dialysis at ( 70 – 80 gm/dl ) to avoid over
dialysis, and measure urea level after dialysis.
 Causes of abnormal blood urea

1- prerenal : any condition may effect transport of urea to kidney

( congestive heart failure )
In this case there will not be decrease in blood volume, but also the heart in failure state
and will not pump the blood ( plasma ) to kidney, so will decrease renal blood supply and
decrease in excretion of urea ( urea will not reach to kidney ).
( shock, hemorrhage, dehydration )
share the same mechanism to decrease plasma volume, the body will prefer to pump this
small amount of blood to vital organs such as heart and lung, and avoid pumping it to
kidney, so will decrease renal blood supply and decrease in excretion of urea ( urea will
not reach to kidney ).
( increase protein catabolism, high protein diet )
In this cases, there will be increase in production of urea rather than problem in transport
of urea.

2- Renal : any condition effect the kidney

( Acute and chronic renal failure, renal disease, including glomerular nephritis, tubular
necrosis )

3- postrenal :
( urinary tract obstruction )
• In male, the most common causes is enlargement of prostate [ benign prostate
hypertrophy ]
• In female, the most common causes is [ urinary stone ]

4- Decreased concentration
( low protein intake, severe vomiting and diarrhea, liver disease, pregnancy )
Will increase plasma and decrease urea
Notes :
Urea is freely diffusible in and out of RBC and Plasma , So it can be measured in whole
blood , Plasma and Serum.
Q/ why we can be measured urea in whole blood , Plasma and Serum ?
Answer / because it is uncharged and freely diffusible in and out of RBC and Plasma

Whole blood should be deproteinized to eliminate Hb interference.

Sample should be analyzed within several hours of collection to avoid effect of

bacterial action. Why ?
Answer : because of bacterial enzyme action ( urease ), that can destroyed urea and
convert it to ammonia.

Estimation of Blood Urea

❖ Principle
The method based on the following reaction
𝒖𝒓𝒆𝒂𝒔𝒆
• Urea + H2O → 2NH3 + CO2
Salicylate and hypochlorite in the reagent react with the ammonium ions to form a green
complex
the complementary filter we use ( red )

❖ Calculation
𝑨𝒃𝒔 (𝑨𝒔𝒔𝒂𝒚)
• 𝑩𝒍𝒐𝒐𝒅 𝒖𝒓𝒆𝒂 = x conc of standard ( mg/dl)
𝑨𝒃𝒔 ( 𝒔𝒕𝒂𝒏𝒅𝒂𝒓𝒅)

𝑨𝒃𝒔 (𝑨𝒔𝒔𝒂𝒚)
• 𝑩𝒍𝒐𝒐𝒅 𝒖𝒓𝒆𝒂 = x 50 ( mg/dl)
𝑨𝒃𝒔 ( 𝒔𝒕𝒂𝒏𝒅𝒂𝒓𝒅)

• Normal Range = 15 - 45 mg/dl

❖ Rapid Method

Blank Standard Test

Working Reagent (R1) 1 ml 1 ml 1 ml

( contain urease )

Standard 10μ ml
( known conc.
Of urea )
Serum 10μ ml
( unknown conc.
Of urea )

Demineralised Water 10μ ml

Mix and stand at room temperature for 5 min

( urea → ammonia )

Sodium hypochlorite( R2) 200 μ ml 200 μ ml 200 μ ml

( react with ammonia )
Mix and stand at room temperature for 10 min, Measure at 600 nm