Urine protein (Proteinuria)

Sample for Urine protein (Proteinuria)

• A random urine sample can be used.

Indications for Urine protein (Proteinuria):

1. To find out the presence or absence of protein in the urine.
2. This may be used as a screening test for kidney disease, particularly to screen for diabetic nephropathy.

Pathophysiology of Urine protein (Proteinuria):

1. 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:

1. Pre-renal proteinuria is not indicative of renal disease.
   1. This transient condition is caused by low-molecular-weight plasma proteins like hemoglobin, myoglobin, and acute-phase proteins.
   2. Another example is Bence-jones proteinuria in cases of multiple myeloma.
2. Renal proteinuria is seen in renal diseases where there is glomerular or tubular damage.
   1. In the case of glomerular damage, there is an increased amount of albumin with RBCs and WBCs.
3. Post-renal may be due to causes in the ureters, urinary bladder, prostate, and vagina.
   1. The causes are bacterial and fungal, which produce exudate-containing protein from the interstitial fluid.
   2. The blood, as a result of injury or menstrual cycle, contributes to protein.
   3. Prostatic fluid and spermatozoa may also contribute to protein.

Mechanism of protein in the urine:

1. Urine is formed by the ultrafiltration of plasma across the glomeruli.
2. Plasma protein with molecular weight >40,000 is retained in the plasma.
3. Normally glomerular membrane does not allow filtration of protein into the urine because of narrow spaces in the glomerular membrane.
   1. The majority of the albumin presented to the glomeruli is not filtered.
   2. The convoluted tubules reabsorb much of the Protein (albumin) filtered by the glomeruli.
4. 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.

5. Albumin is 1/3 of the urinary protein.
   1. Albumin filtered through glomeruli very easily in comparison to plasma globulin.
6. In pathologic conditions, Albumin is abundant.
7. Urine Albumin is used as the protein marker of glomerular permeability.
8. The term proteinuria is often used synonymously with Albuminuria.
9. Protein is the single most important parameter for renal dysfunction.
10. If more than a trace of protein is found in urine, advise 24 hours urinary protein.

Procedure to detect proteinuria:

Spot test:

1. In this test, protein is detected by dipstick or biochemically in the random urine sample.
2. Usually, 24 hours urine sample is needed.
3. Urine protein assays are sensitive to all types of proteins like albumin, globulins, and Bence-Jones protein.
4. Most of the assays can detect a minimum of 3 mg/dL of protein in the urine.
5. A urine dipstick is most commonly used. This is most sensitive to albumin.
   1. The dipstick can detect albumin when it is about 18 mg/dL.

Sulfosalicylic acid precipitation method:

1. First, centrifuge the urine.
2. Add 3 mL of 3% sulfosalicylic acid (another reference says 20%) to 3 mL of centrifuged urine.
3. Mix well, observe cloudiness, and the photometry can also read this.

Grade based on turbidity	Degree of Turbidity	Protein % in mg/dL
Negative	No change	<6 mg/dL
Trace	Can see turbidity Faint white precipitate	6 to 30 mg/dL
1+	Distinct turbidity with no granules Can see written letters	30 to 100 mg/dL
2+	Turbidity with granules No flocculation Can not see written letters	100 to 200 mg/dL
3+	Turbidity with granules Flocculation can not be through	200 to 400 mg/dL
4+	Precipitation/clumps or gel tube	>400 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.

Source 1

• 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
Negative	Negative	Negative	Negative
Trace	Trace	5 to 20 mg/dL	Trace
1+	30 mg/dL	30 mg/dL	30 mg/dL
2+	100 mg/dL	100 mg/dL	200 mg/dL
3+	300 mg/dL	300 to 500 mg/dL	≥500 mg/dL
4+	>2000 mg/dL	>500 mg/dL	No color change

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:

Pre-renal causes:

1. Multiple myelomas.
2. Intravascular hemolysis.
3. Muscle injury.
4. Infection and inflammation.

Renal causes:

1. Glomerular diseases:
   1. Amyloidosis.
   2. Immune-complex disease.
   3. Diabetic nephropathy.
   4. Hypertension.
   5. Pre-eclampsia.
   6. Strenuous exercise.
   7. Dehydration.
   8. Toxic agents.
   9. Orthostatic or postural.
2. Tubular diseases:
   1. Drug toxicity is like toxic agents and heavy metals.
   2. Fanconi’s syndrome.
   3. Viral infection (severe).

Post-renal causes:

1. Lower urinary infection.
2. Menstrual contamination.
3. Vaginal secretion.
4. Injury or trauma.
5. Prostatic fluid.
6. Presence of spermatozoa.

Microalbuminuria

• 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.

---