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Urinalysis - basic concepts

Kidney, as excretory organ, excreted metabolites, in particular, nitrogenous end products of protein and other analytes. Furthermore, as an endocrine organ, the kidneys participate in the metabolism of the renin-angiotensin and the kinin-kallikrein system, the glucose metabolism, produce erythropoietin, prostaglandin, vitamin D.

Urine is the end product of renal activity. The formation and excretion of urine by the kidneys is carried by glomerular filtration and diffusion, tubular reabsorption and secretion. The functional activity of the kidneys leads to the maintenance of acid-base balance and regulation of electrolyte and water balance of the body, the regulation of the osmotic state of the blood and tissues, contributes to maintaining homeostasis.

Urine contains water, metabolites, electrolytes, trace elements, hormones, vitamins, exfoliated cells and tubules urinary tract mucosa, leukocytes, salts mucus.

Structural-functional unit of kidney is nephron, which consists of a glomerulus and tubule. The glomerular filtrate (primary urine) contains all low molecular weight non-protein part of blood plasma, in the same concentration as in plasma. Primary urine specific gravity - 1,010; pH - 7.4; viscosity - 1.02. Primary urine contains proteins with molecular mass less than 70 kDa. Their number varies from 30-50 up to 70-80 mg per day.

In the renal tubule occurs reabsorption and substances secretion due to activity of renal tubular epithelium. Reabsorption of substances from the primary urine, and secretion by renal epithelium into the lumen of the tubules substances from capillaries near-tubular or formed in tubular epithelium, leads to the formation of the final urine.

Proximal tubule cells mainly provide the preservation of most of the substances, filtered at the glomerulus. They reabsorbed protein, amino acids, glucose, vitamins, various electrolytes and about 80% water. About the proximal tubule is judged by the transport of glucose.

Loop of Henle (thin segment of the tubule) acts as a counter-duplicating systems: two adjacent tubules in which the fluid flows in the opposite direction, ensuring the processes of concentration and dilution of urine.

The distal tubules and collecting ducts carry the stability of acid-base status, regulate the constancy of the water balance and electrolyte composition of the internal environment of the body, providing a certain blood concentration of ions - K, Na, Ca, Mg, Cl, HPO4 and others. The maintenance of acid-base status also depends on the ability of renal epithelial cells to secrete substances (H-ions as a result of acidogenesis and ammonia due to the renal ammonium synthesis), which replaces Na, keeping alkaline valence to the body, and as the basis used for removal of acid valences.

Osmotic dilution of urine and its concentration allows to make a conclusion about the state of the distal segment of the nephron and collecting ducts.

Collecting tubes are a continuation of the distal tubule. Ending in papillae, collecting tube opens into the renal calyx. From there, the urine flows through the ureters into the bladder. The structure of the walls of the renal calyx, pelvis, ureters, bladder, excretory ducts of the prostate and urethra are similar. Their mucosa is lined with transitional epithelium. Stratified squamous epithelium lined the urethra, vagina, external genitals of the woman and the distal (outer) part of the urethra men.

In normal urine sediment can be found a small number of squamous cells and isolated cells of transitional epithelium. Increasing the number of transitional epithelial cells and the appearance of the renal epithelium is characteristic of kidney and urinary tract diseases.

The basis of kidney disease is damage of glomerular membrane or tubular epithelial by inflammatory, infectious, toxic, or other processes, or genetically determined defect, causing a impaired structure and function.

There are kidney disease, mainly affecting the glomeruli (acute and chronic glomerulonephritis, nephro-angiosclerosis, nephrosis) and with a primary lesion of the renal tubules (acute and chronic pyelonephritis, acute and chronic renal insufficiency of any etiology).

General characteristics of urine

Urine volume

Formation of urine depends on air temperature, exercise, rest and sleep. The mechanism of reducing urine output during sleep due to the action of antidiuretic hormone of the posterior lobe of the pituitary. Muscular exercise leads to a decrease in renal plasma flow rate that causes a decrease in sodium excretion. Heat reduces glomerular filtration, causing oliguria, and also reduces the excretion of sodium.

Urine volume generated per day also depending on age:

  • newborns - 0–60 ml
  • children in the first month of life - 200–350 ml
  • children 1–5 years - 600–900 ml
  • children 10–14 years - 1000–1500 ml
  • adults - 1000–2000 ml

Normally, an increase in urine output (polyuria physiological) occurs at:

  • taking plenty of fluids
  • eating certain foods (watermelons, melons and other fruits)

Physiologic oliguria (reduced urine output) occurs at:

  • restriction of fluid intake
  • increased sweating, vomiting, diarrhea (extrarenal factors)
  • in preterm infants

Rare urination (olakisuria) - a physiological phenomenon in the first days after birth.

Frequent urination (physiological pollakisuria) — when receiving large amounts of fluid.

The ratio of daytime and nocturnal urine normally ranges from 4:1 to 3:1.


Urine volume change in pathology

Urine volume
Polyuria — is an increase in the daily amount of urine. - resorption of edema, transudate, exudates
- after the febrile conditions
- primary aldosteronism
- hyperparathyroidism
- nephrosclerosis
- diabetes insipidus and diabetes mellitus
Polyuria intermittent Hydronephrosis
Polyuria paroxysmal In nervous, mentally excitable children
Oliguria — is a reduction of daily amount of urine. - feverish conditions
- cardiac disease
- acute renal failure
- nephrosclerosis
Anuria — is absence of urine. - acute renal failure
- severe nephritis
- meningitis (reflectively)
- intoxications
- peritonitis
- tetany
- blockage of the urinary tract by tumor or stone
Olakisuria — is an infrequent urination - in neuro-reflex disorders
Pollakiuria — is a frequent urination. - inflammation of the urinary tract, colds
- in nervous, mentally excitable children
Dysuria — is a painful urination. - uric acid infarct of newborns
- vulvovaginitis
- cystopyelitis
- urethritis
Enuresis — is an urinary incontinence. - inflammation of the urinary tract
- convulsions
- severe feverish conditions
- CNS diseases
- myelitis
- in neurotic children like nocturnal enuresis
Nocturia — is the prevalence of nocturnal diuresis above daily diuresis. - an initial stage of cardiac decompensation
- cystitis
- cysto-pyelitis


Urine color

Normally, urine is straw-yellow in color. Discoloration of urine is possible in a number of physiological and pathological conditions.

Urine color
Urine color causes
Normal urine
Amber or straw-yellow Urochrome A and B, uroerythrin, urobilin and hematoporphyrin
Physiological hyperchromeuriah Oliguria (limit drinking, sweating, the use of carrots as food)
Physiological hypochromeuriah Polyuria (increased drinking, diuretic foods)
Hyperchromeuriah - diarrheas
- toxicosis
- fever
- vomiting
- liver disease
- heart disease
- hemolytic condition
Hypochromeuriah - diabetes mellitus
- diabetes insipidus
- nephrosclerosis
Red or pink-red - hematuria
- porphyrinuria
- red streptocide, amidopyrine, antipyrine, santonin and sulfazole drugs intake
Green or blue - methylene blue intake
- in severe obstructive jaundice (biliverdin)
Intensely yellow or brown - bilirubinuria
- methemoglobinuria
- porphyrinuria
- hemoglobinuria
- myoglobinuria
Milky white - Lipiduria or lipuria, chyluria (lipids in urine)
Black-brown - alkaptonuria (AKU)
- melanosis
- salol and naphthol intake
Orange - riboflavin intake


Urine appearance

Normal urine is clear. When standing in the container it forms a light haze. Clouding is caused by crystals of urine (crystalluria), cellular elements, bacteria, mucus, and fat.


Urine odor

Freshly collected urine has no odor. Smell of ammonia is observed when standing normal urine in patients with cystitis, pyelitis, pyelonephritis. If ketonuria appears "apple" and "fruit" odor. The sharp smell of urine by eating garlic and horseradish.


Urine pH level

The reaction of normal urine (with mixed food) acid or neutral (pH 5,5–7,0), but more often the pH is about 5-6. Standing urine (in container) released carbonic acid and the pH shifted to the alkaline side. The reaction of urine can vary depending on diet: protein foods causes the pH shifts to the acid side, the predominance of carbohydrate foods — to the alkaline side.

Urine pH level
Blood pH level
Acidic Acidic - diabetes (precoma, coma-ketones)
- feverish conditions
- starvation
- renal insufficiency
- renal tuberculosis
- leukemias
Alkaline Alkaline - cystitis, pyelitis
- hematuria
- after vomiting and diarrhea
- during resorption of exudate, transudate
- soda and mineral water intak
Alkaline Acidic - hyperchloraemic acidosis
- renal tubular acidosis
- chronic urinary tract infections (bacterial decomposition of urine nitrogen compounds to ammonia)
Acidic Alkaline - hypokalemic (low potassium) condition (paradoxical aciduria)


Urine specific gravity

Urine specific gravity (SPEC GRAV) ranges from 1.001 to 1.040 in adults and 1.002–1.030 to the child of early age, and in the first days after birth is 1.022–1.020. The SPEC GRAV depends on the amount of fluid, concentration of protein in the urine, glucose, calcium, etc. So the SPEC GRAV is proportional to the weight concentration of substances dissolved in it. The definition of a SPEC GRAV is used to assess the concentration function of the kidneys.

High urine specific gravity, up to 1.030–1.034, often can be observed:

  • in morning urine samples of healthy individuals, especially in the summer season
  • in febrile patients due to the increased release of urea, uric acid, creatinine, a reduced amount of urine
  • during amyloid and lipoid nephrosis
  • in diabetes mellitus, alimentary glycosuria
  • in "congestive kidney"

In elderly patients with diabetes mellitus due to atherosclerotic renal vascular changes reduced the filtration process. Urine specific gravity varies between 1.020–1.024 at a very reasonable glycosuria. Low urine specific gravity is observed in the excretion of large quantities of urine (polyuria) and organic lesions of the kidneys.