Bones can break, muscles can atrophy, glands can loaf, even the brain can go to sleep, without immediately endangering our survival, but should the kidney fail ..... neither bone, muscle, gland nor brain could carry on”
                                    Homes W. Smith


Kidneys play a major role in sustaining life. They keep the body’s internal environment in balance and play a vital role in maintaining normal homeostasis. A variety of diseases may affect the kidney and lead to progressive nephron loss. As kidney function deteriorates, loss of excretory, regulatory and endocrine functions takes place and complications develop in virtually every organ system. Therefore screening of patients for renal disease both by high clinical suspicion and prompt laboratory backup becomes the prime responsibility of a practising clinician.

SCREENING METHODS
Any patient with a history of oliguria, periorbital oedema, generalised oedema (generally perceived as an increase in weight, increase in clothes size or ring size) or any person with history of diabetes, or hypertension in self or in the family should undergo a complete renal evaluation to rule out any renal disease.

A complete examination of urine, renal function tests like BUN, serum creatinine, plain X-ray KUB, and ultrasonogram (USG) for detecting kidney size are the minimum necessary tools required in detecting a renal disease.

1. Urine examination:

A. Macroscopic examination

Colour: Colour of the urine provides useful information. Normal colour of the urine is straw yellow. Deep yellow indicates concentrated urine or jaundice. Red urine indicates haematuria, myoglobinuria, porphyria or beetroot ingestion. Cloudy urine indicates an infection and milky urine indicates chyluria, pyuria or phosphaturia. Urine that turns dark on standing indicates porphyria or alkaptonuria.

Specific gravity: The normal urine specific gravity ranges from 1.000 to 1.015. A fixed specific gravity of 1.010 is a feature of renal insufficiency.

Proteins: Proteinuria is usually indicative of renal disease. Normally, small amounts of protein (approximately 150 mg/ 24 hours) are excreted in urine. Mild proteinuria can occur in chronic interstitial disease, febrile illness and congestive cardiac failure. It may also be detected in severe urinary tract infection. Large amount of protein (3g/day or more) is indicative of a glomerular disease. When 24 hours collection of urine is difficult (as in urinary fistulae or in children), a urine protein/ urine creatinine ratio can be calculated in a spot urine sample. A value of <0.3 is normal, 0.3 to 3.0 is due o the presence of mild to moderate proteinuria and > 3.0 is massive proteinuria.

Pyuria: Pyuria is defined as “pus in urine” or as the presence of 10 or more white blood cells per mm3 in fresh mid-stream urine. This is abnormal and indicates inflammatory reaction along the urinary tract. Sterile pyuria can occur in the following conditions: acute febrile episode, glucocorticoid therapy, cyclophosphamide administration, pregnancy, renal transplant rejection, genito-urinary trauma, stress and UTI during the course of antibiotic treatment.

Bacteriuria: Bacterial counts of more than 105/mm3 indicates significant bacteruria.
Microalbuminuira: Urinary albumin excretion less than 20 to 200 mcg/min is referred as micro albuminuria. It is a particularly useful test for detecting incipient diabetic nephropathy.
Bence Jones proteins: These are light chains excreted by patients suffering from monoclonal gammopathies such as multiple myeloma.

Glycosuria: Renal glycosuria is a frequent finding in the elderly where renal threshold for glucose is lowered below the normal of 180 mg/d or in inherited tubular defects (e.g. Fanconi’s syndrome). It is also a hallmark of diabetes.


2. Biochemical tests :
The standard laboratory investigations include plasma concentration of urea, creatinine, electrolytes (sodium, potassium, chloride, bicarbonate), calcium, phosphorus and uric acid and urinary estimation of protein, urea, creatinine and electrolytes. Quantification of renal function involves study of glomerular and tubular functions.

Causes of abnormal blood urea levels
Blood urea levels are increased in renal failure, low protein diet and old age (reduced catabolism). BUN/creatinine ratio greater than 15 is abnormal and indicates pre- or post-renal azotemia or conditions associated with urea overproduction. A low ratio is found in pregnancy, overhydration, severe liver disease and malnutrition.

3. Other screening aids

These include imaging studies such as:

1. Plain x-ray abdomen: Bony changes of osteodystrophy common in chronic renal failure can     be identified.
2. Ultrasonography: The size of the kidneys can be delineated and cortical thickness can be     monitored. It helps to distinguish between obstructive parenchymal disease and solid and     cystic masses.
3. Intravenous urography (IVU): Serves as the primary screening method for structural and     functional status of the kidneys.

Other screening modalities reserved for special circumstances include:

• Cystography and micturating cysto-urethrography (MCU): Useful in evaluation of
   vesico-ureteric reflux (VUR).
• Doppler study: Useful in investigating renovascular hypertension, and in studying renal blood    flow during renal transplant surgery or in renal artery stenosis.


CONCLUSION

Screening can decrease the risk of complications of chronic kidney disease and prevent kidney failure. Studies demonstrate that if renoprotective therapies are initiated early, a patient can live a normal life span without developing end-stage renal disease (ESRD). Consequently an integrated approach of high clinical suspicion, with biochemical and haematological backup and other imaging tests can provide a comprehensive approach to screening various kidney diseases.