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Pathophysiology · Additional topics

Urea in urinalysis

Urea

Although in everyday practice patients often search for information about "urea in urine", clinicians evaluate the nitrogen-excreting function comprehensively. To do this, the level of serum urea is examined in inseparable conjunction with urinalysis (UA) indicators.

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FiltrationIn renal failure, filtration is impaired, and blood urea levels rise sharply.
SynthesisIn hepatitis and cirrhosis, urea levels drop due to decreased hepatic synthesis.
FeverIntoxication causes transient changes in urinalysis (increased specific gravity, proteinuria, leukocyturia).
MonitoringIn chronic kidney disease (CKD), urinalysis and urea tests are mandatory minimum diagnostics.
3 min readFor medical studentsUpdated 10.10.2026
Material prepared by WhiteCoat Pro editorial team based on platform study guidesPending instructor review

Comprehensive assessment of nitrogen-excreting function

A single indicator is insufficient for a full assessment of renal function. Clinical practice utilizes a standardized set of primary markers:

  • Determination of urea concentration in blood serum.
  • Determination of creatinine concentration in blood serum.
  • Calculation of the glomerular filtration rate (GFR).
  • Assessment of relative urine specific gravity (evaluated both in a single urinalysis and via the Zimnitsky test).

Differential diagnosis by urea level

Blood urea concentration is highly sensitive to pathologies of various body systems. Changes in this indicator help differentiate renal and extrarenal problems.

Pathological processUrea levelPathomechanism
Renal failureSignificantly elevated (retention azotemia)Impairment of normal glomerular filtration
Hepatitis, liver cirrhosisDecreasedDecrease in hepatic synthetic function
Cachexia, trauma, burnsElevated (production azotemia)Enhanced breakdown of tissue proteins
High-protein dietElevated (alimentary azotemia)Excessive dietary nitrogen intake
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Transient urinary changes in infections

Against the background of dehydration and intoxication (e.g., in pneumonia, opisthorchiasis, moderate-to-severe ARVI), pathological signs may appear in the general urinalysis.

With pronounced fever and intoxication syndrome, the following are frequently detected:

  • Increased urine specific gravity.
  • Mild leukocyturia.
  • Proteinuria (protein in urine).
  • Cylindruria.

It is important to understand that these changes are transient. They resolve on their own once body temperature normalizes and intoxication is relieved. In uncomplicated viral infections (e.g., uncomplicated herpes simplex or ARVI), pathological changes in urine and blood tests are usually absent.

In severe specific infections, the clinical picture worsens. Thus, severe herpetic stomatitis is accompanied by albuminuria, cylindruria, and microhematuria in the urinalysis, while biochemical blood analysis records elevated creatinine and urea levels. In severe shigellosis, urinalysis also reveals mild proteinuria, microhematuria, cylindruria, and leukocyturia alongside elevated blood urea.

Monitoring in internal organ diseases

Blood biochemistry with urea determination and general urinalysis are essential tools for monitoring patient status:

  1. Preoperative minimum: urea is tested in lymphomas, malignant neoplasms, and aortic aneurysms.
  2. Chronic heart diseases: in hypertrophic cardiomyopathy, aortic regurgitation, and infective endocarditis, regular monitoring (Level of Reliability of Evidence C, Level of Reliability of Data 5) of urinalysis and biochemistry (urea + creatinine) is indicated every 6–12 months to detect renal involvement in the pathological process.
  3. Acute conditions: in hemorrhagic fever with renal syndrome, evaluation of urea, creatinine, and total protein levels is mandatory.

Class and exam questions

These are transient changes occurring against the background of high fever and intoxication. After recovery and normalization of temperature, the indicators return to normal on their own.

These are transient changes occurring against the background of high fever and intoxication. After recovery and normalization of temperature, the indicators return to normal on their own.

A decrease in urea is characteristic of liver damage (hepatitis, cirrhosis), as urea synthesis occurs specifically in the liver.

A decrease in urea is characteristic of liver damage (hepatitis, cirrhosis), as urea synthesis occurs specifically in the liver.

This is a sharp increase in blood urea caused by impaired glomerular filtration in renal failure (the kidneys cannot excrete nitrogen normally).

This is a sharp increase in blood urea caused by impaired glomerular filtration in renal failure (the kidneys cannot excrete nitrogen normally).

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What else to study on this topic

  • Calculation and clinical significance of the glomerular filtration rate (GFR).
  • Zimnitsky test: methodology and interpretation of results.
  • Coprological examination in intestinal infections (shigellosis).
  • The role of the liver in protein metabolism and mechanisms of urea formation.
  • Changes in liver transaminases (ALT, AST) in infectious hepatitis.

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