Urine sample Types, Urine Formation, and Composition
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
- 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.
- This will contains an increased concentration of analytes and cellular elements.
- 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
- This sample is needed for the culture and sensitivity of urinary infection.
- The patient is advised to clean the urethra, then discard the first few mL of urine.
- Now midstream of the urine is collected in the sterile container.
5. 24 Hours of a urine sample
- In this case, discard the first urine and note the time.
- Now collect urine in the container for 24 hours and put the last sample in the container.
- Refrigerate the sample.
- These 24 hours of samples are needed to measure urea, creatinine, sodium, potassium, glucose, and catecholamines.
6. Supra-pubic collection of the urine sample
- This is done in the patients who cannot be catheterized, and the sample is needed for culture.
- With the help of a needle, a urine sample is collected.
7. Catheter collection of urine
This is done in patients who are bedridden and can not urinate.
8. Pediatric urine sample
- In infants, special collection bags are made adherent around the urethra.
- Then urine is transferred to a container.
Urine storage and preservation (Precautions):
- 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.
- To prevent bacterial growth, immediately refrigerate the urine.
- Light sensitive chemicals are protected by keeping the urine in a colored bottle like amber plastic bottles.
- Precipitation of calcium and phosphate can be prevented by acidifying the urine.
- To see the crystals, casts, RBC, and white cells, freshly voided and concentrated urine is needed.
- Ideally, urine should be examined within one hour of collection.
- Sodium fluoride can be added to estimate 24 hours of glucose. It inhibits the growth of bacteria.
- 10 ml of HCl (6N) is added to the containers for the estimation of VMA.
The indications of urine examination
- This is part of the routine workup of a patient.
- It can diagnose urinary tract infections.
- It can diagnose diabetes.
- Diagnose any abnormality of metabolism.
Pathophysiology of urine
- The kidneys continuously form urine.
- 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.
- Ultrafiltrate has constituents like plasma, so this is called ultrafiltrate.
- Each nephron (one glomerulus unit) can filter 100 µL ultrafiltrate per day.
- The total ultrafiltrate formed is 170 to 200 L/day.
- After absorption, the urine formation is 0.4 to 2 L/day.
- Urine is a mixture of water, which is about 96% and 4% are dissolved substances.
- Urea is about one-half of the dissolved substances.
- The main substances are sodium, potassium, urea, creatinine, calcium, magnesium, phosphate, sulfates, and ammonia.
- An average of 170,000 ml/day of plasma passes from the kidney, and an average of 1200 ml of urine is formed/day.
- The role of Kidneys:
- Clear the body waste products.
- Maintain the water and electrolyte balance.
- This selective function in the nephron is controlled by:
- Renal blood flow.
- Glomerular filtration.
- Tubular reabsorption and secretion.
- Urine concentration and dilution occur in the renal medulla.
- Kidneys Functions:
- To concentrate or dilute the urine.
- Regulate sodium excretion.
- Regulate Blood chemistry.
- Regulate Fluid balance.
- Regulate nutrients intake.
- Regulate blood pressure.
- Composition of the Urine:
- organic substances are:
- Uric acid.
- Inorganic substances are:
- Traces of Ammonia.
- organic substances are:
- Other substances are: