Urea

DESCRIPTION:
Urea is the main metabolic product of nitrogenous substances in our body. It is formed from ammonia and CO2 in the Krebs-Henseleit cycle in the liver. It is freely filtered through the glomeruli, and 40-50% of urea is passively reabsorbed in the proximal tubules. The molecular weight of urea is 60 daltons. There are 2 nitrogen atoms in the urea molecule, accounting for 28, so the urea to nitrogen ratio is 2.14 (60/28).

DETERMINATION:
The method for urea determination is a kinetic UV method. The sample for analysis is serum, plasma (heparin), or urine. Sample stability is 5 days at 2°C to 8°C.

CLINICAL SIGNIFICANCE:
1) Physiological changes in urea concentration. Urea concentration depends on diet. Individuals consuming a high-protein diet have a slightly higher serum urea concentration than those on a low-protein diet. Urea is normally lower in children and women due to less muscle mass compared to adult men. A) Increased values: In normal individuals, blood urea concentration increases with higher protein intake / Urea concentration increases with age / In late pregnancy due to increased protein intake. B) Decreased values: Blood urea concentration is lower in growing children than in adults / In the early stage of normal pregnancy / In individuals on a low-protein, high-carbohydrate diet. 2) Pathological changes in urea concentration. A) Increased urea concentration in cases of: Excessive urea production / High-protein food intake 12 hours before blood collection / Increased catabolism of body proteins / Incomplete excretion of urea from the body / Renal insufficiency / Postrenal insufficiency / Prerenal insufficiency / Acute pancreatitis / Acute post-streptococcal glomerulonephritis / Acute kidney failure / Atherosclerosis / Benign prostatic hypertrophy / Heavy chain disease (gamma) / Liver cirrhosis / Cystinosis / Diabetes mellitus / Gout / Glomerulonephritis / Goodpasture’s syndrome / Hydronephrosis / Hyperthyroidism / IgA nephropathy / Intestinal obstruction / Bladder carcinoma / Cholera / Congestive heart failure / Chronic lymphocytic leukemia / Chronic kidney failure / Chronic pyelonephritis / Leptospirosis / Medullary cystic disease / Membranoproliferative glomerulonephritis / Multiple myeloma / Nephrotic syndrome / Non-Hodgkin’s lymphoma / Polycystic kidney disease / Vomiting / Pre-eclampsia / Septicemia / SLE / Acquired hemolytic anemia (autoimmune) / Shock / Lead poisoning / Urethritis / Liver failure. B) Decreased urea concentration in cases of: Acromegaly / Acute and subacute liver necrosis / Liver disease / Celiac disease / Liver cirrhosis / Cystic fibrosis / Eclampsia / Hepatolenticular degeneration / Laennec’s or alcoholic cirrhosis / After hemodialysis / After glucose infusion / Nephrotic syndrome / Pre-eclampsia / Protein malnutrition / Toxic hepatitis / Liver failure.

RISK FACTORS:
Decreased values:
– Diurnal rhythm: morning – Fasting – Smoking – Pregnancy
Increased values:
– Dehydration – Diurnal rhythm: afternoon – Season: summer – Nephrotoxic drugs – Stress – Shock – Physical exertion – Trauma

EFFECT OF MEDICATIONS:
Decreased values:
amikacin, ascorbic acid (conc. > 20 mg/L), cefotaxime, dipyrone, fluorides, caproxamine, chloramphenicol, levodopa, streptomycin
Increased values:
acetohexamide, amino acids, aminophenol, aminosalicylic acid, asparagine, citruplexin, cotrimoxazole, dextran, hydantoin derivatives, phenylurea, guanethidine, chloral hydrate, chloramphenicol, sulfonylurea, tetracyclines

RESULT:
The reference interval depends on sex, age, and the determination method. The reference interval is displayed on every validated report.