Newcastle Laboratories

Urea, serum

Clinical Background:

The formation of urea and its excretion by the kidneys represents the major route (c. 75%) by which nitrogen is removed from the body. It is an end product of metabolism and in the kidneys the cont...

The formation of urea and its excretion by the kidneys represents the major route (c. 75%) by which nitrogen is removed from the body. It is an end product of metabolism and in the kidneys the contribution of urea to medullary hypertonicity is important in determining the kidney’s ability to concentrate urine.
Urea has traditionally been used as a renal marker but has limited value for this purpose when compared to creatinine. Plasma/serum levels depend on the rate of its formation and the rate of excretion. Although the major excretory route is the kidneys about 10% is lost in sweat and via the gut. A variable quantity of filtered urea is reabsorbed so that the amount excreted is not an accurate measurement of the GFR.
Circumstances related to renal disease where urea may be useful are;
*Suspected pre-renal failure e.g. due to fluid depletion or cardiac failure.
*In monitoring the effects of renal replacement treatment
*Predicting the severity of acute pancreatitis.
Suspected inherited metabolic disease (low levels seen in urea cycle disorders)
Interpretation of urea levels is made more difficult by it being influenced by 3 factors;
*Its rate of synthesis (reflecting protein turnover)
*The volume of distribution (total body water)
*Rate of its excretion (determined by rate of glomerular filtration and tubular reabsorption).

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Test Details

  • Discipline:

    Biochemistry

    Biochemistry

  • Specimen Container Adult:

    Serum-SST

    Serum-SST

  • Specimen Container Paediatric:

    Serum-Plain tube

    Serum-Plain tube

  • Minimum Volume Adult:

    1 mL blood

    1 mL blood

  • Minimum Volume Paediatric:

    0.5 mL blood

    0.5 mL blood

  • Sample Stability:

    - Unseparated: 1 day

    - Separated:

    at room temperature: 7 days
    at 4°C: 7 days

    - Unseparated: 1 day

    - Separated:

    at room temperature: 7 days
    at 4°C: 7 days

  • Interpretation:

    Causes of high urea levels
    Renal failure
    Dehydration due to;
    1. Low fluid intake
    2. Excessive fluid loss e.g Vomiting, diarrhoea, excessive sweating, inappropriate diuretic use, conditions causing ...

    Causes of high urea levels
    Renal failure
    Dehydration due to;
    1. Low fluid intake
    2. Excessive fluid loss e.g Vomiting, diarrhoea, excessive sweating, inappropriate diuretic use, conditions causing polyuria (DM/Diabetes Insipidus)
    Decreased renal perfusion;
    1. Hypovolaemia
    2. Systemic hypotension
    3. Cardiac failure
    High protein turnover and generation of waste nitrogen;
    1. High muscle mass
    2. High protein intake
    3. Gastrointestinal haemorrhage
    4. Catabolic states eg. Trauma, sepsis and corticosteroid treatment


    Causes of low urea levels
    Low values are uncommon and include
    Decreased protein turnover;
    1. Low protein intake e.g.starvation
    2. Low body muscle mass
    Increased total body water;
    1. Over hydration
    2. Pregnancy
    Decreased urea synthesis;
    1. Inherited disorders of the urea cycle
    2. Liver failure
    Ammonium heparinate leads to elevated results

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  • Reference Ranges:

    0 - 4w: 0.8 - 5.5 mmol/L
    4w - 1y: 1.0 - 5.5 mmol/L
    1y - 16y: 2.5 - 6.5 mmol/L
    16y and over: 2.5 - 7.8 mmol/L

    0 - 4w: 0.8 - 5.5 mmol/L
    4w - 1y: 1.0 - 5.5 mmol/L
    1y - 16y: 2.5 - 6.5 mmol/L
    16y and over: 2.5 - 7.8 mmol/L

  • Other Info:

    Plasma- Lithium Heparin also acceptable

    Plasma- Lithium Heparin also acceptable

  • Routine Contact Name:

    Duty Biochemist

  • Routine Telephone:

    Freeman: 0191 244 8889
    RVI: 0191 282 9719

    Freeman: 0191 244 8889
    RVI: 0191 282 9719

  • Routine Email:

Availability:

All times
All sites

Turn Around:

Urgent: within 1 hour

Non-urgent: within 4 hours

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