Abnormal constituents

1. Proteins

Normal value: The amount of protein excreted in normal urine is insignificant and constitute not more than 20-80mgs per 24hrs.

Note: In abnormal conditions: As much as 20gms or more proteins may be excreted in urine. It probably consists of albumin, globulins and mucoproteins from blood.

Ratio of albumin:globulin being more than 10:1.

Tamm-Horsfall protein: A glycoprotein, a relatively small amount is found in normal urine. It is secreted by the mucous glands of the normal genitourinary tract. It has a mol.wt of approx. 30000. Function – probably it serves to protect the epithelial cells of the tract.

Proteinuria

When proteins appear in urine in detectable quantities, it is called as albuminuria. Actually albuminuria term is a misnomer, as seldom albumin found alone, hence the term “proteinuria” is to be preferred.

The proteins that are found in the urine in kidney conditions are commonly believed to be plasma proteins that pass through the damaged renal epithelium.

The albumin having smallest molecules pass most easily; globulins next and fibrinogen least readily. There are many pathologic conditions that cause proteinuria, which may be classified in three major groups.

1. Pre-renal; (b) Renal; (c) Post-renal.

1. Pre-renal Conditions causing proteinuria of this group are those that are primarily not related to kidney. In most cases, they affect the kidneys in such a way as to render it more permeable to the protein molecule.

Causes

1. Cardiac diseases – by affecting the circulation of kidneys leads to proteinuria.

2. Any abdominal tumors, or mass of fluid in the abdomen does the same by exerting pressure on the renal veins.

3. Fevers, covulsions, anaemias and other blood diseases, Liver diseases and many other pathologic states can affect in similar manners as stated above.

4. Cancers: an increased amount of urinary mucoproteins generally accompanies elevated serum mucoprotein levels. Such has been observed in patients with cancers, with highest values when carcinomatous invasion is widespread.

5. Collagen diseases and inflammatory conditions also have high mucoprotein levels.

2. Renal

Proteinurias are found in various types of kidney diseases and are called as “Renal proteinurias”.

Causes:

1. Acute glomerulonephritis – is always associated with proteinuria.

2. Chronic glomerulonephritis – proteinuria is sen in early stages, but may disappear later as the kidney becomes more and more impaired.

3. In nephrosclerosis, T.B. of kidney and in carcinoma of kidney – Proteinuria is frequently found but it is not always.

4. In nephrotic syndrome – (Type II) large quantities of albumin is lost in the urine and there may be gross hypoalbuminaemia in blood.

5. Polypeptides, the so-called, proteoses and peptones, sometimes are excreted in urine. This may happen in pneumonias, diphtheria, carcinoma and other conditions – is due to some protein containing materials eg an exudate or a tissue mass/pus undergoing autolysis.

3. Post-renal These are sometimes called as “false” proteinurias, whereas the above two are “true”, because in these conditions (post renal) proteins do not pass through the kidneys.

Causes:

1. May be due to inflammatory, degenerative or traumatic lesions of the pelvis of the kidney, ureter, bladder, prostate or urethra.

2. Bleeding in genitourinary tract also will account for proteinuria

3. Urine containing pus also contains proteins, since the exudate that accompanies the pus is rich in proteins

2. Sugars (Glucose) Glucose is appeared in urine when its level in blood plasma is more than renal threshold of glucose, which is equal 8.8mM/L. There are renal and extrarenal-glucosuria. Renal glucosuria may be due to some renal diseases in which is destroyed mechanism of reabsorption of glucose in kidneys, for example syndrome Fanconi etc. In these cases the level of glucose in blood plasma may be in normal range, but it is not reabsorbed in kidneys and is excreted in urine. Extrarenal glucosuria is observed in Diabetes Mellitus and other conditions when the level of glucose in blood plasma is increased (is more than its renal threshold). Glucosuria is accompanied by polyuria, hyperstenuria and polydypsia.

3. Ketone bodies Ketonuria is observed in hyperketonaemia, for example in Diabetes Mellitus, Starvation and other conditions, when the lipolysis and ketogenesis are increased.

4. Blood-Haematuria Passing of whole blood including erythrocytes in urine is called as Haematuria. It is a result of haemorrhage in urinary tract. Sometimes the shade or appearance gives a clue as to the site of bleeding.

Causes: The haemorrhage can be due to any of the variety of causes.

1. Injury to kidney or urinary tract.

2. Violent exercise

3. Infection of the urinary tract

4. Benign or malignant neoplasma of kidney or urinary tract

5. In benign enlargement of prostate due to rupture of endorged veinous plexus

6. Administration of certain drugs e.g., salicylate, methenamine, sulphonamides, Barbiturates, anticoagulants

7. Parasites – Schistosomiasis (by S. haematobium)

8. Allergic reactions

9. Low prothrombin levels

Note: Haemoglobinuria refers to excretion of free Hb following increased plasma level of free Hb (Haemoglobinaemia). It appears as pink or light red oxy-Hb in alkaline urine and as brown methaemoglobin or brownish deoxygenated Hb in acid urine.

Note:

1. There is a renal threshold for Hb, and normally a reabsorption from the renal tubules. When this threshold is exceeded, haemoglobinuria results. Apparently, Hb when it is in solution in blood plasma, treated by the body as a foreign substance and is excreted in the urine.

2. When the threshold is exceeded and free Hb is excreted in the urine, Hb may precipitate in the tubules if the urine is acid in reaction. Hence in the treatment of haemoglobinuria e.g., following incompatible blood transfusion, the administration of alkalies may prove to be helpful.

5. Bile Salts and Bile Pigments are appeared in urine in hepatic and obstructive jaundice.

References

Main literature:

1. M. Edwin – Biochemistry in clinical correlation, 2001

2. Harper’s Biochemistry – R.K. Murray, D.K.Granner, P.A.Mayes, V.W.Rodwell – Connecticut, 2000

3. U. Satyanarayana – Biochemistry – Books and Allied (P/LTD, Kolkata (India), 2002

4. M.N. Chatterjea, R. Shinde – Textbook of Medical Biochemistry – Jaypee Brothers, New Delhi (India), 1995

Additional literature:

1. Ozols J: Amino acid analysis. Methods Enzymol. 1990; 182:587

2. Biemann K: Mass spectrometry of peptides and proteins. Annu Rev Biochem 1992; 61:977

3. Benner S.A. et al: Predicting the conformation of proteins from sequences: Progress and future progress. Adv Enzyme Regul 1994; 34:269

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