About Laboratory Testing for Proteinuria

Proteinuria is a medical condition generally described as protein amounts in a person’s urine at higher levels than normal. It’s a condition sometimes witnessed in healthy people, but it’s more often related to abnormalities or various diseases.

Plasma, which is the liquid component of blood, has a variety of different proteins. The human kidneys serve many roles, and one of them is the conservation of the plasma protein, so it doesn’t get eliminated with actual waste products during the creation of urine. There are primarily two different ways the human body typically keeps protein from escaping into a person’s urine:

  • First, the glomeruli offer a barrier that just physically keeps most bigger plasma proteins within the blood vessels.
  • Second, the tubules reabsorb nearly all the smaller proteins which do get through.

Proteinuria happens most often when there is damage to the glomeruli or tubules inside the kidneys. Scarring and/or inflammation of the glomeruli may result in larger volumes of protein leaking into the urine, and possibly even red blood cells, or RBCs. Tubule damage can also mean proteins don’t get absorbed back in. This condition might also occur if there isn’t a lot of protein within the blood to start with, and the kidney tubules aren’t able to absorb it all back in.

Healthy individuals can be afflicted with proteinuria in both temporary and persistent forms. This condition might also be related to cold exposure, aspirin therapy, fever, exercise, and stress. Some individuals release more of their protein through urine when they’re standing up as compared to lying down; this specific condition is known as orthostatic proteinuria, but it’s rarely seen in those past the age of 30. On the other hand, when there is a detectable protein level in someone’s urine, it typically highlights the possibility of an underlying condition or disease. Further analysis is typically warranted to ascertain the specific cause.

The most frequent reason for protein levels in a person’s urine is due to kidney damage, which can be the result of:

Diabetes: Proteinuria is often an early sign of kidney function deterioration in those with either type 1 or 2 diabetes.

Hypertension: Proteinuria can also be an early warning signal of deteriorating kidney function in an individual diagnosed with high blood pressure.

Other reasons for kidney damage that lead to proteinuria include but are not limited to the following:

  • Congestive heart failure, or CHF
  • Toxin exposure
  • Infections
  • Trauma
  • Immune disorders like IgA nephropahty, lupus, or Goodpasture’s syndrome, among others
  • Kidney Cancer
  • Other conditions that might result in a case of proteinuria include the following:
  • Intravascular Hemolysis: This is the destruction of red blood cells and the release of hemoglobin within the bloodstream.
  • Pre-Eclampsia: Pregnant and expecting women get screened or tested regularly by physicians, given the presence of proteinuria is related to toxemia of pregnancy or pre-eclampsia. This disorder is specific to pregnancy, and it’s usually when hypertension and proteinuria wind up developing simultaneously. Symptoms might include headaches, nausea, and swelling or edema during pregnancy. In rare cases, it can even cause serious symptoms, like seizures. Pre-eclampsia is potentially hazardous for both mother and child.
  • Multiple Myeloma: This is also known as a cancer of a person’s plasma cells. When proteinuria happens because of Bence-Jones proteins, or excess blood protein overflowing into a person’s urine, then they might have multiple myeloma. Bence-Jones proteins have atypical immunoglobulin light chains, designated as either lambda or kappa, which monoclonal plasma cells produce. Every immunoglobulin has four protein chains; two of them are light chains, and the other two are heavy chains. Bence-Jones protein has a pair of immunoglobulin light chains, and the presence of it in a person’s urine can be a diagnostic indicator of multiple myeloma, when in the proper context of certain other symptoms also manifesting.

Symptoms and Signs

Lab testing is currently the only surefire method of accurately determining the presence of protein in a patient’s urine. Many health organizations even suggest that individuals at risk for contracting chronic kidney disease get urine testing done routinely. Proteinuria often involves no symptoms, particularly in mild situations. High levels of protein in a person’s urine might create a foamy appearance. If the blood loses a lot of protein, it can impact how capable a body is at regulating fluids. This can result in edema, which is the swelling of a patient’s abdomen, feet, hands, and face. When symptoms do show up, they’re typically related to a specific disease or condition, which results in proteinuria.

Testing

Testing specifically for proteinuria covers several goals. These include the evaluation of kidney functions, condition detection, screening at-risk individuals, ascertaining underlying causes, and analyzing the kinds and quantities of proteins that are getting released. When proteinuria is officially detected, then the patient will go through regular monitoring to watch out for the condition resolving or deteriorating. Proteinuria testing involves both blood and urine tests.

Laboratory Tests

Screening for urine protein can be part of a regular doctor’s appointment, or also as part of checking up on any patient known to be diagnosed with a condition that might trigger proteinuria. Some of the potential screening tests can include the following:

Urine Protein: This should detect the presence of all sorts of proteins that might be in a person’s urine. This can be a standalone test using a random sample of urine or part of a broader urinalysis.

Urinalysis: This evaluates a urine sample for multiple substances that might be present in a person’s urine, which includes proteins. This test is sometimes used as a component of a broader health exam.

Microalbumin/Urine Albumin: This is a sensitive test useful for monitoring diabetes patients for smaller volumes of albumin in their urine. Albumin is the primary blood protein, and diabetes can impact kidney function over time. That makes this test an early warning sign that kidney damage is happening because of diabetes. The American Diabetics Association suggests that those already diagnosed as being type 2 diabetic get annual screenings for low albumin levels in their urine. They also recommend that type 1 diabetes patients get their first test within five years of diagnosis, followed by annual testing after that.

A screening test that yields a positive result might involve follow-up urine testing to establish what kinds of protein are getting lost through urine, as well as what volumes:

Urine Albumin 24-Hours: This test measures how much albumin is being lost through urine over a period of 24 hours. This test can provide a healthcare practitioner with a good idea of how much kidney damage is happening.

Urine Albumin/Creatinine Ratio: This test can use a random urine sample instead of gathering up all urine for a full day. Creatinine is an additional measurement in this scenario. Creatinine is released into a person’s urine at a normally steady rate of flow. When a random sample is analyzed for both creatinine and protein, then it’s possible to compute the albumin/creatinine ratio of the urine at that time. This calculation corrects for how creatinine there is in a random sample, which offers more precise insight into how much albumin is being lost through a person’s urine.

Urine Protein 24-Hours: This day-long test measures how much protein gets released into a patient’s urine over a period of 24 consecutive hours. It offers higher levels of accuracy in measuring proteinuria as compared to random urine tests.

UPCR: The urine protein/creatinine ratio measures creatinine and protein in the same random sample, before correcting the creatinine volume. This is very similar to the tests for urine albumin/creatinine ratio.

Urine Protein Electrophoresis: This test is useful for ascertaining the various kinds and associated volumes of proteins that are present within a person’s urine. This urine test is effective for determining the presence of the Bence-Jones protein, meaning it’s occasionally employed if a medical provider suspects multiple myeloma.

When any protein electrophoresis demonstrates the presence of an abnormality, then an immunofixation test might be the follow-up that quantifies any abnormal proteins, along with an immunoassay evaluation to look for free light chains.

On top of urine testing, a handful of other tests are useful in analyzing kidney function and/or evaluating the specific nature of a protein that is in a person’s urine. Such tests might be done as follow-ups or simultaneously to urine protein screening. These tests can include:

Blood Urea Nitrogen (BUN) And Creatinine: These blood tests are effective ways of evaluating kidney functions. Both creatinine and urea are waste products that contain nitrogen; healthy kidneys will move these from a person’s blood into their urine. When kidneys aren’t working right, then creatinine and urea stay in a person’s bloodstream, meaning that their levels go up. It should be noted that while creatinine can get measured through urine samples, blood samples also go through measurement for an inclusive evaluation.

Estimated Glomerular Filtration Rate (eGFR): This combines blood creatinine levels, age, and gender and ethnic variables to estimate a urine filtration rate. Progressive kidney damage lowers a person’s eGFR rate.

Creatinine Clearance: This measures creatinine levels in a 24-hour sample of urine, as well as a blood sample. The objective is calculating how much creatinine has been removed from a person’s blood through the urine. The known rate of excretion of creatinine from a person’s body is insightful in how well a person’s kidneys are functioning.

TP (Total Protein): This blood test can measure the totality of protein in serum.

Albumin: This blood test is a measurement of how concentrated albumin is.

Serum Protein Electrophoresis: This ascertains the kinds of related volumes of protein in a blood sample. Medical experts compare it to a urine electrophoresis pattern to see if a person’s bloodstream is the cause or urine protein.

SFLC (Serum Free Light Chains): This blood test can assist in the diagnosis and monitoring of conditions related to higher production levels of free light chains, as can happen with multiple myeloma.