Dr. NK Hase, in the fourth part of the proteinuria series answers questions on urine protein electrophoresis, protein evaluation, creatinine estimation and the role of kidney biopsy in determining aetiology, prognosis, and therapy.

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What is the role of urine protein electrophoresis (UPEP)?

Urine protein electrophoresis (UPEP) may be recommended to find out type and amount of proteins excreted. UPEP detects 2 types of proteins- albumin and globulins. Normally, urine albumin is less than 5 to 10 mg/dL and globulins are absent. A characteristic monoclonal band M spike is often found in monoclonal gammopathy multiple myeloma.

Immunofixation electrophoresis is done to detect the type and amount of light chains- kappa, lambda, heavy chains and immunoglobulins. Bence Jones proteinuria is not used as a screening test nowadays as it lacks sensitivity. This is replaced by serum-free light chain assays.

In selective proteinuria, UPEP shows predominantly, albumin, alpha 1 globulin and transferrin. Non-selective proteinuria UPEP pattern in often non-specific like mirror image to that of serum. Selective proteinuria is seen in minimal change disease. Non-selective proteinuria is seen in nephrotic syndrome due to Focal segmental glomerulosclerosis (FSGS), membranous, and amyloidosis.

What are the different methods used for evaluation of urinary proteins and creatinine?

As there is no reference method, a large variety of methods are used to estimate proteins in urine. Commonly used methods are dry chemistry, turdbidometric, and dye-binding methods. All these methods do not give comparable analytical sensitivity and specificity for all proteins.

High analytical variability was noted among colorimetric and turdbidometric methods used for total urinary proteins estimation. It is advised to follow up with the same laboratory for follow up purposes.

Creatinine estimation methods

1. Jaffe method: This is the most commonly used method. Creatinine reacts with picrate, giving a yellow-orange colour that is proportional to the creatinine concentration. The non-creatinine chromogens: acetoacetate, pyruvate, ketoacids, proteins, glucose, ascorbic acid, bilirubin or even some drugs like cephalosporins also react with picrate giving higher readings.
2. Enzymatic method: Studies indicated that the analytical specificity, sensitivity and precision are better for the enzymatic assays compared to the Jaffe assays. It is more expensive than Jaffe method.

The creatinine method should be calibrated to the isotope dilution mass spectrometry (IDMS) assay. A total analytical error goal for creatinine measurement should not exceed 10%. The recommendations for creatinine measurements are to use an enzymatic assay to decrease random errors and an IDMS traceable assay to decrease systematic errors.

What is relationship between foamy urine and proteinuria?

Historically persistent foamy urine noticed on voiding is considered as a warning sign of kidney disease. Foamy urine is characterised by appearance of multiple layers of small to medium bubbles in urine voided into a container. The appearance of single layer of larger bubbles upon voiding that quickly dissipate can be consider normal.Traditionally, foamy urine has been considered by physicians as well as patients as a marker of proteinuria.

Only 1/3 of patients complaining of foamy urine are found to have abnormal proteinuria. In most of the cases, the cause remains unexplained. The foams are formed by trapping pockets of gas in liquids with the help of surfactant. A surfactant is an organic compound that is amphiphilic meaning, containing both hydrophobic and hydrophilic ends. A surfactant diffuses in water and adsorbs at interface between air and water where water insoluble hydrophobic end aggregate form bubbles..The foam in beer is dependent on an amphipathic protein (lipid transport protein 1) derived from barley. In general, protein or polypeptide have amphiphilic properties that can function as a surfactant and form a foam in the urine.

What is the role of biopsy in patients with proteinuria?

Kidney biopsy will help to determine the aetiology, prognosis and decide specific therapy.

1. A kidney biopsy is indicated in all adults with proteinuria more than 3.5 g/day with or without nephrotic syndrome.
2. In patients with non-nephrotic range proteinuria 1 to 3 g/day with active urinary sediments (dysmorphic RBCs, RBC cast, WBC, WBC cast, acanthocytes) or decreased GFR, kidney biopsy will be indicated to find out exact aetiology.
3. In patients with non-nephrotic range proteinuria with glomerular haematuria and rapidly increasing serum creatinine with or without systemic symptoms, kidney biopsy will be indicated to rule out crescentic glomerulonephritis.
4. In patients with isolated proteinuria less than 1 g and non-nephrotic range proteinuria in diabetes, kidney biopsy is not indicated.
5. Patients with isolated proteinuria 1 to 3 g (non-nephrotic range) without serologic biomarkers should be followed by nephrologists; biopsy should be considered for worsening of proteinuria or kidney function.

In the last part, Dr. NK Hase will discuss case discussions on the topic.

Disclaimer- The views and opinions expressed in this article are those of the author's and do not necessarily reflect the official policy or position of M3 India.

The author Dr. NK Hase is a Director clinical Nephrology & Transplant working at Jupiter Hospital, Thane and former Professor & Head of Department of Nephrology Seth GS Medical College and KEM Hospital, Mumbai.