Urine sample Types, Urine Formation, and Composition

March 22, 2021Lab TestsUrine Analysis

Type of urine samples

1. Random sample 

This is a diluted urine sample and may give an inaccurate interpretation of patient health. But it is best to do microscopy to evaluate WBC or RBC.

2. First Morning sample

1. This is the best sample for microscopy and urine analysis. This is the concentrated urine because urine remained throughout the night in the urinary bladder.
2. This will contains an increased concentration of analytes and cellular elements.
3. Urine must have remained in the bladder for 8 hours is considered as the first-morning sample.

3. Urine for sugar (Postprandial 2 hours)

The postprandial 2 hours sample was collected after 2 hours of a high carbohydrate diet.

4. Midstream clean catch urine

1. This sample is needed for the culture and sensitivity of urinary infection.
2. The patient is advised to clean the urethra, then discard the first few mL of urine.
3. Now midstream of the urine is collected in the sterile container.

5. 24 Hours of a urine sample

1. In this case, discard the first urine and note the time.
2. Now collect urine in the container for 24 hours and put the last sample in the container.
3. Refrigerate the sample.
4. These 24 hours of samples are needed to measure urea, creatinine, sodium, potassium, glucose, and catecholamines.

6. Supra-pubic collection of the urine sample

1. This is done in the patients who cannot be catheterized, and the sample is needed for culture.
2. With the help of a needle, a urine sample is collected.
   

   Supra-pubic aspiration of the urine from the urinary bladder of the female patient

7. Catheter collection of urine

This is done in patients who are bedridden and can not urinate.

8. Pediatric urine sample

1. In infants, special collection bags are made adherent around the urethra.
2. Then urine is transferred to a container.

Urine storage and preservation (Precautions):

1. To keep urine constituents intact, preservation of the urine is essential. If urine is not preserved, that will leads to a change in the number of bacteria and chemicals.
2. To prevent bacterial growth, immediately refrigerate the urine.
3. Light sensitive chemicals are protected by keeping the urine in a colored bottle like amber plastic bottles.
4. Precipitation of calcium and phosphate can be prevented by acidifying the urine.
5. To see the crystals, casts, RBC, and white cells, freshly voided and concentrated urine is needed.
6. Ideally, urine should be examined within one hour of collection.
7. Sodium fluoride can be added to estimate 24 hours of glucose. It inhibits the growth of bacteria.
8. 10 ml of HCl (6N) is added to the containers for the estimation of VMA.

 The indications of urine examination

1. This is part of the routine workup of a patient.
2. It can diagnose urinary tract infections.
3. It can diagnose diabetes.
4. Diagnose any abnormality of metabolism.

Pathophysiology of urine

1. The kidneys continuously form urine.
2. This process is basically ultrafiltration of plasma or blood where glucose, amino acids, water, and important metabolically active substances needed for the body are absorbed.
   1. Ultrafiltrate has constituents like plasma, so this is called ultrafiltrate.
   2. Each nephron (one glomerulus unit) can filter 100 µL ultrafiltrate per day.
   3. The total ultrafiltrate formed is 170 to 200 L/day.
      

      Summary of the urine formation

3. After absorption, the urine formation is 0.4 to 2 L/day.
   

   Summary of the Urine formation

Urine composition

1. Urine is a mixture of water, which is about 96% and 4% are dissolved substances.
   1. Urea is about one-half of the dissolved substances.
   2. The main substances are sodium, potassium, urea, creatinine, calcium, magnesium, phosphate, sulfates, and ammonia.
2. An average of 170,000 ml/day of plasma passes from the kidney, and an average of 1200 ml of urine is formed/day.
   

   Water reabsorption in various part of the kidneys

6. The role of Kidneys:
   1. Clear the body waste products.
   2. Maintain the water and electrolyte balance.
7. This selective function in the nephron is controlled by:
   1. Renal blood flow.
   2. Glomerular filtration.
   3. Tubular reabsorption and secretion.
8. Urine concentration and dilution occur in the renal medulla.
9. Kidneys Functions:
   1. To concentrate or dilute the urine.
   2. Regulate sodium excretion.
   3. Regulate Blood chemistry.
   4. Regulate Fluid balance.
   5. Regulate nutrients intake.
   6. Regulate blood pressure.
10. Composition of the Urine:
    1. organic substances are:
       1. Urea.
       2. Creatinine.
       3. Uric acid.
    2. Inorganic substances are:
       1. Chloride.
       2. Sodium.
       3. Potassium.
       4. Traces of Ammonia.
11. Other substances are:
    1. Hormone.
    2. Vitamins.
    3. Medications.
    4. Cells.
    5. Casts.
    6. Crystals.
    7. Mucous.
    8. Bacteria.