Urine Protein (Proteinuria), Spot Test, Microalbuminuria
Urine protein (Proteinuria)
Sample for Urine protein (Proteinuria)
- A random urine sample can be used.
Indications for Urine protein (Proteinuria):
- To find out the presence or absence of protein in the urine.
- This may be used as a screening test for kidney disease, particularly to screen for diabetic nephropathy.
Pathophysiology of Urine protein (Proteinuria):
- There will be no proteins in the urine in a healthy individual with normal renal function, or you may find only traces.
Proteinuria is divided into:
- Pre-renal proteinuria is not indicative of renal disease.
- This transient condition is caused by low-molecular-weight plasma proteins like hemoglobin, myoglobin, and acute-phase proteins.
- Another example is Bence-jones proteinuria in cases of multiple myeloma.
- Renal proteinuria is seen in renal diseases where there is glomerular or tubular damage.
- In the case of glomerular damage, there is an increased amount of albumin with RBCs and WBCs.
- Post-renal may be due to causes in the ureters, urinary bladder, prostate, and vagina.
- The causes are bacterial and fungal, which produce exudate-containing protein from the interstitial fluid.
- The blood, as a result of injury or menstrual cycle, contributes to protein.
- Prostatic fluid and spermatozoa may also contribute to protein.
Mechanism of protein in the urine:
- Urine is formed by the ultrafiltration of plasma across the glomeruli.
- Plasma protein with molecular weight >40,000 is retained in the plasma.
- Normally glomerular membrane does not allow filtration of protein into the urine because of narrow spaces in the glomerular membrane.
- The majority of the albumin presented to the glomeruli is not filtered.
- The convoluted tubules reabsorb much of the Protein (albumin) filtered by the glomeruli.
- In glomerulonephritis, the glomerular membrane is injured, and there are larger spaces from where the protein, particularly albumin (smaller in size), can easily pass in the urine.
- Albumin is 1/3 of the urinary protein.
- Albumin filtered through glomeruli very easily in comparison to plasma globulin.
- In pathologic conditions, Albumin is abundant.
- Urine Albumin is used as the protein marker of glomerular permeability.
- The term proteinuria is often used synonymously with Albuminuria.
- Protein is the single most important parameter for renal dysfunction.
- If more than a trace of protein is found in urine, advise 24 hours urinary protein.
Procedure to detect proteinuria:
- In this test, protein is detected by dipstick or biochemically in the random urine sample.
- Usually, 24 hours urine sample is needed.
- Urine protein assays are sensitive to all types of proteins like albumin, globulins, and Bence-Jones protein.
- Most of the assays can detect a minimum of 3 mg/dL of protein in the urine.
- A urine dipstick is most commonly used. This is most sensitive to albumin.
- The dipstick can detect albumin when it is about 18 mg/dL.
Sulfosalicylic acid precipitation method:
- First, centrifuge the urine.
- Add 3 mL of 3% sulfosalicylic acid (another reference says 20%) to 3 mL of centrifuged urine.
- Mix well, observe cloudiness, and the photometry can also read this.
|Grade based on turbidity||Degree of Turbidity
||Protein % in mg/dL|
NORMAL urine protein
- Spot urine protein = 0 to 8 mg/dl
- While 24 hours of protein is <150 mg/dl
- Another source
- <10 mg/dL or
- 100 mg/24 hours of urine.
- The limits of detection by the strips are:
- Albustix , Multi stix = 15 to 30 mg/dL.
- Chemstrip = 6 to 30 mg/dL.
- In the case of microalbumin:
- Albsure = 2 to 3 mg/dL
- Micral = 1.5 to 2 mg/dL
- Micro-Bumintest = 4 to 8 mg/dL
Comparison of various urine protein tests:
|Grade of urine protein||Multistix/Albustix||Sulfosalicylac acid||Chemstrip|
Sensitivity of the various test strip:
- Multistix/Albustix = 15 to 30 mg/dL of albumin.
- Chemstrip = 6 mg/dL of albumin (in 90% of the cases).
Causes of urine proteinuria:
- Multiple myelomas.
- Intravascular hemolysis.
- Muscle injury.
- Infection and inflammation.
- Glomerular diseases:
- Immune-complex disease.
- Diabetic nephropathy.
- Strenuous exercise.
- Toxic agents.
- Orthostatic or postural.
- Tubular diseases:
- Drug toxicity is like toxic agents and heavy metals.
- Fanconi’s syndrome.
- Viral infection (severe).
- Lower urinary infection.
- Menstrual contamination.
- Vaginal secretion.
- Injury or trauma.
- Prostatic fluid.
- Presence of spermatozoa.
- This indicates diabetic nephropathy.
- There is reduced glomerular filtration, and eventually, there is a renal failure in diabetes mellitus type 1 and type 2.
- Diabetes complication is first indicated by microalbuminuria.
- These complications are controlled by controlling the diabetic glucose level and hypertension.
- Microalbuminuria is also associated with cardiovascular disease.
Values are reported as the albumin excretion in µg/minute or mg/24 hours.
- Microalbuminuria is significant when:
- It is 20 to 200 µg/minute Or
- 30 to 300 mg/24 hours Or
Normal urine picture:
Physical features Chemical features Microscopic findings
- Color = Pale yellow or amber
- Appearance = Clear to slightly hazy
- pH = 4.5 to 8.0
- Specific gravity = 1.015 to 1.025
- Blood = Negative
- Glucose = Negative
- Ketones= Negative
- Protein = Negative
- Bilirubin = Negative
- Urobilinogen = Negative (±)
- Leucocyte esterase = Negative
- Nitrite for bacteria = Negative
- RBCs = Rare or Negative
- WBC = Rare or Negative
- Epithelial cells = Few
- Cast = Negative (Occasional hyaline)
- Crystal = Negative (Depends upon the pH of the urine)
- Bacteria = Negative Albumin: creatinine ratio is >3.4 mg/mmol.
- See more details on the urinary protein.