The patient who often urinates

Gastroepato

Urine is formed by the work of two equal organs which, as we know, are the kidneys. The heart, in conditions of health, generates a thrust on the renal filter and this pressure, which is exercised through the renal artery, is able to allow renal filtration. The functional unit of the kidney that functions as a filter is the nephron (see side), ie a microscopic tubule able to filter the blood and collect the filtrate that will give rise to the urine.
The true renal filter consists of a set of thin vessels that curl up to form a dense network of capillaries: the glomerulus, contained in a sort of calyx called Bowman's capsule, from which originate a contiguous series of tubules, called, in order, proximal contorted tubule, loop of Henle and distal convoluted tubule, for a total length of 5 centimeters. More distal tubules from different nephrons flow into the collecting tubule, at the extremity of which urine is collected. The principle on which a nephron works is the following: all the blood is filtered as preurina, a total of 180 liters / day and what is needed is reabsorbed for a total of about 178.5 liters. It follows, therefore, that normally only the waste products pass through the urine, ie water and nitrogenous waste, dissolved in 1.5 liters of urine or less, without the presence of proteins, hyaline cylinders, red blood cells, bacteria and white blood cells, mucus-pus etc.
The presence of such substances and / or cells is a very serious sign in medicine. The final product of the filtration flows into the renal pelvis and then, through a small tube called ureter, into the bladder, where it accumulates before being excreted through the urethra.

Alteration of the renal filtrate

There is talk of polyuria when the amount of urine is excessive and this is a sign of serious pathology. These are generally abundant urine, often pale, like water, more than 3000 ml / day. It is usually the patient who urinates at night, when he is lying down and this may depend on an increased venous return in heart failure, but sometimes he recognizes innocent causes such as the banal hydration, that is the mania to drink so much, especially those who do sports and even go to "water intoxication"! These are depressed women, who drink up to 3-4 liters a day and have headache and blurred vision, with high blood pressure and weight gain. At other times, excessive coffee consumption also stimulates thirst and polyuria, due to the characteristic of coffee which is diuretic, or the consumption of alcohol, the excessive ingestion of salt, glucose and hyperosmolar substances. But some drugs can also give polyuria, such as loop diuretics (furosemide). Only in rare cases, for brain tumors with suppression of the antidiuretic hormone or ADH, which regulates the balance of fluids on the absorption of the renal tubule, excessive diuresis may occur.

Generality

Anamnesis, ie collection of patient's news

Because the patient with polyuria may develop hypovolemia, one should carefully evaluate its state of volemia and hydration and monitor vital signs, especially body temperature, tachycardia and orthostatic hypotension. Is the patient tired? Is it thirsty, is it hypotensive or hypertensive? Are there any alterations in the investigations of renal relevance: azotemia, creatinine, sodemia, my potassium and creatinine clearance? Does the chemical-physical urine have microalbuminuria or frank proteinuria and high sediments? Is he tired and breathless and hungry for air? Does it have high blood sugar? Do you simply need to urinate often but your urination is limited? Does it suffer from pollachiuria, then small jets of urine, with burning? Do you suffer from prostatic hypertrophy? Is there blood in the urine? Do you suffer from burning when you urine? If a woman, did she have any loss from the vagina? Is he a conscious patient, in good health or has suffered from episodes of illness with cerebral vasculopathy and, for example, does not control the sphincters (cf. stroke)? Or is he a patient who has had neurological problems and does not feel when he loses urine? Is his spinal cord intact? Have there been any traffic accidents or anything else? After the doctor has collected this information, we can now go, in short, to describe the causes of polyuria.

Medical causes of polyuria

Acute tubular necrosis

It is a rare but very serious pathology of nephrological relevance, it means in the diuretic phase a damage of the renal tubules, ie of the organelles responsible for the reabsorption of water in the kidney, so a patient can urinate even 8 liters / day, but it is urine with a low specific gravity, like water of 1.005. Signs are weight loss and severe dehydration.

Insipid diabetes

Very rare disease with polyuria of even 5 liters / day, accompanied by polydipsia, nocturia, asthenia and dehydration.

Diabetes mellitus

Very frequent cause of polyuria which rarely exceeds 5 liters / day, and specific weight of 1,020. The patient presents polydipsia, polyphagia, weight loss, weakness and infections of the urinary tract. The cause lies in the fact that the renal filter to which an excessive glucose carbox due to impaired metabolism reaches, can re-establish glucose up to the threshold of 160 mg / dl, after which the glucose passes into the urine with osmotic polyuria.

Glomerulonephritis

In these patients, polyuria evolves towards oliguria and the diursis is less than 4 liters / day. The associated signs are anorexia, asthenia, declining edema, headache, hypertension and dyspnoea. There may be malodorous or foamy haematuria and urine.

Hypercalcemia

Potassium depletion can lead to nephropathy with polyuria usually less than 5 liters / day, with specific weight of 1.010, polydipsia, nocturia, constipation, anorexia and vomiting.

Hypokalaemia

Low potassium levels can lead to renal tubule damage with polyuria of less than 5 liters / day and specific weight of 1.010, arrhythmias.

Post-obstructive urea

For example after an obstruction of the renal tubules, with polyuria up to 5 liters / day, bladder distension and edema with nocturia.

Pyelonephritis

Causes polyuria less than 5 liters / day with a low but variable specific weight, other signs of high fever and low back pain.

Drugs

The loop diuretics, the furosemide used in the treatment of heart failure can give polyuria, cardiotonic, vitamin D, phenytoin, lithium, methoxyflurane.

Pollakiuria

Here the sign is frequent urination, usually in the elderly who suffers from prostatic hypertrophy, with stagnation of urine and the emission of fetid and frequent urine for concomitant acute cystitis. Or if there is prostatitis, bladder cacry, multiple sclerosis and urinary urgency, prostate cancer, rectal cancer, urethral strictures, marrow injuries.

nephrology topics