Protein in Urine: What, How & Why


Proteinuria

 

WHAT IS PROTEINURIA?

The leakage of Plasma Protein in urine is technically termed as “Proteinuria” (pronounced as pro-teen-you-reah). These proteins are NOT the usual nutrient that you obtain from food. These are a different class of Proteins specially made by your Liver.

Plasma Proteins normally circulate in your bloodstream & help with a range of functions essential to keep you alive. Urine samples with Protein tend to be visibly foamy / frothy akin to the kind that you get after dissolving detergents in water. The extent of foam will certainly vary with the extent of protein leakage.



 

Unlike bubbles in normal urine that disappear after a few seconds of flushing, the foam in urine with protein continues to persist and sometimes even becomes frothier after you flush the toilet. The image below depicts this fact well.

Protein in urine -- flushed Toilet

Presence of such proteins in urine can be easily confirmed by means of a Dip-Strip test during a Urine Routine Examination (Urinalysis).

Proteinuria specimen - protein in urine

 

IS PROTEIN IN URINE ABNORMAL?

Some very tiny proteins can sometimes be filtered in urine normally in very minute quantities between 8-10 milligrams in a day (1). These quantities are low enough to escape detection with even ultra-sensitive Dip-Strips used to look for Protein in Urine during Urine Tests. These proteins are NOT a cause for concern.

However, if Dip-Strip tests detect protein in the urine, it is usually when the quantity is beyond 30 milligrams in 24 hours. For all practical purposes, this is abnormal, however trivial the cause may be.



 

Based on how long protein leakage lasts in the patient’s urine, Proteinuria is of the following types:

1. TRANSIENT PROTEINURIA

Also called Benign Proteinuria, this is temporary or in some cases, an on-and-off condition. Here, patients typically lose less than 1-gram protein a day. It may sometimes be present with Dehydration, Fever, Exercise, Emotional Stress, Obesity and in a condition called Sleep Apnoea.

Temporary leakage of protein in urine is abnormal and requires regular monitoring. However,  it is certainly NOT a cause for alarm in terms of Kidney Health, until the patient continues to present with protein in urine in multiple instances over 3 months or more. If that is the case, the proteinuria is said to have turned “Sustained”.

2. SUSTAINED PROTEINURIA

Commonly associated with Kidney Disease, protein leakage persists in the patient’s Urine for over 3 months. Most patients lose more than 1 gram of protein in urine per day. Such patients must undergo proper clinical & laboratory workup for assessment of their Kidney health status.

 

Keeping in sync with the focus of this website All Things Kidney – Official, we will limit our explanation on Sustained Proteinuria found in Kidney Disease.

 

 

HOW DO HEALTHY KIDNEYS PREVENT PROTEIN LEAKAGE IN URINE?

Normally, when blood loaded with toxic wastes reaches the kidneys for filtration, it enters the kidneys through one of the large pipelines called the “Renal Artery”. 

Once within the kidney, the blood distributes via numerous tiny branches of blood vessels to individually reach out to each one of the 1-1.5 million individual Nephrons (“filtration units”) of the kidney for efficient filtration. That’s just one of the ways how Mother Nature applies “Division of Labour” within our body!

Blood vessels reach each nephron and form an entangled, scrunched-up loop to “sit on the cup-like head of the nephron”. This entangled loop of blood vessels is called the “Glomerulus” (glom-er-you-lus). Remember this name! Because this is where all the barrier action against leakage of proteins in Urine takes place.

Image A below points out the Glomerulus of one nephron in a kidney.

Glomerulus magnified view | www.allthingskidney.com

 

A healthy kidney has 1-1.5 million nephrons working together to carry out all the crucial functions. Hence, each kidney has over a million glomeruli (plural of glomerulus) or filtration units.

The Glomerulus is a beautifully intricate piece of work by Mother Nature. This portion of blood vessels has a special lining of a 3-layered filtration system to cater to the ultra-selective nature of kidney filters.

The image B below depicts the filter arrangement.

Glomerular Protein in urine

It is Nature’s tactful provision of “chemically charge” over filter surfaces, progressively decreasing pore dimensions across filtration layers and their tight-knit geometry that guards against “Glomerular Proteinuria” — the hallmark of Kidney Disease.

Protein in urine Glomerulus banner

This delicate “pore-size & charge-based barrier action” is vulnerable to get compromised if there is something that’s constantly shoving, pushing-through & damaging the filtration layers in the Glomerulus over a period of time. As a consequence, either protein or both protein & red blood cells may start leaking into the Urine.

 


WHAT CAUSES THE LEAKAGE OF PROTEIN IN URINE IN KIDNEY DISEASE?

Depending on the cause of kidney disease, protein leakage in Urine can happen in two ways:

Red tick 1 Either due to damage to the either, or all the layers of the Blood Filtration Barrier in the Glomerulus (as explained above) — Glomerular Proteinuria

OR

Red tick ProteinuriaDue to the failure of nephrons to re-absorb the tiny proteins that may occasionally cross the barrier and enter the Urine.

 

 

LIST OF COMMON CONDITIONS CAUSING GLOMERULAR PROTEINURIA
PROTEIN LEAKAGE DUE TO DAMAGE TO THE GLOMERULUS

RENAL CAUSES

1. Diabetic Nephropathy

2. Kidney damage due to High blood pressure

3. Glomerulonephritis

4. IgA Nephropathy

5. FSGS

6. Lupus nephritis

7. Pyelonephritis

8. Nephrotic Syndrome

9. Renal Amyloidosis

10. Advanced stages of Chronic Kidney Disease i.e. Renal Fibrotic Disease (irrespective of root cause)

11. Reflux Nephropathy

NON-RENAL CAUSES

1. Pre-eclampsia

2. Multiple Myeloma

3. Sickle cell Anaemia

4. Some forms of Heart disease such as Endocarditis & Heart failure

PROTEIN LEAKAGE DUE TO FAILURE OF RE-ABSORBING TINY PROTEINS INTO THE BLOODSTREAM

Polycystic kidney disease (ADPKD) (2)

 


 

That is all about the basics of Proteinuria in Kidney Disease.

But then

Protein in urine diagnosis

Click on the image above to get a comprehensive explanation for your questions.

Keep a tab of this space to know more! Till then, stay vigilant about your urine health & Hap-“pee” Learning!

 


REFERENCES:
  1. Harrison Principles of Internal Medicine, 18th Edition, Unit-Nephrology, P 1784
  2. Why does ADPKD cause Protein loss in urine: The Scientist

 


 

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