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Clinical Investigations And Approach In The Diagnosis Renal Diseases
Such investigations include: Urine examination, the specimen (morning sample of urine), specific gravity of urine and others.
This is the single most rewarding investigation in renal diseases. It is absolutely essential, therefore, that the medical student familarises himself with all the tests and their critical evaluation. Fresh urine collected cleanly is examined macroscopically and is subjected to biochemical tests. The centrifuged deposit is examined under the microscope. Further studies like examination of a hanging drop, staining of the deposit for bacteria, culture and cytology are undertaken depending on the indication.
Morning sample of urine is satisfactory. Urine volume is measured by collecting urine for 24 hours. The same can be used for estimating daily loss of proteins, electrolytes and alsoc reatinine clearance. In children in whom 24 hour urine collection is difficult, urine volume can be estimated from a 6 hours or 12 hour collection. For bacteriological culture, a mid-stream urine sample is collected directly into a sterile container after cleaning the external genitalia well with water.
Specific gravity of Urine
Specific gravity of urine is an indirect measure of the solute content and osmolality. Normal specific gravity varies from 1002 to 1030 or more. Specific gravity increases during water deprivation, excessive fluid losses, diabetes mellitus and in some cases of acute glomerulonephritis. It is low in the diuretic phase of nephritis, diabetes insipidus, during clearance of edema and in normals with excessive fluid intake. The specific gravity becomes fixed (isothenuria) in chronic nephritis. The variation in specific gravity brought about by 12 hours fluid deprivation and after administration of a water load is a useful simple test to assess the concentrating and diluting functions of the kidney respectively. Crystalloids increase the specific gravity considerably whereas colloids are less effective in this respect.
Isotope renography helps in assessing renal perfusion and excretory function.
Ultrasonography: This is an investigation of choice for assessing renal size and the presence of obstruction, tumour, cysts and calculi. Moreover-ultrasonography being noninvasive is used more and more extensively.
CT Scan: This helps in clearly visualizing the structural and physical abnormalities.
Renal biopsy: Renal tissue can be obtained by closed needle biopsy. The tissue is processed for histology, microbiological studies, electron microscopy and for immunofluoresence microscopy. Histological diagnosis is necessary for determining the prognosis of several renal disorders like acute glomerulohephritis, nephritic syndrome, lupus erythematosus, amyloidosis etc. It also helps in the planning of the appropriate management.
Urinary Tract Infection
Clinical Approach In Diagnosis
Acute nephritic syndrome
This is characterized by hematuria, red blood cell casts, proteinuria, oliguria, hypertension, fluid retention and varying degrees of renal failure. Many cases are caused by post-streptococcal acute glomerulonephritis. Other causes include disseminated lupus erythematosus polyarteritis nodosa, infective endocarditis and Henoch-schonlein purpura.
This is characterized by massive proteinuria (3.5g in 24 hours). As a consequence of heavy proteinuria, hypoalbuminemia, edema and hyperlipidemia follow.
Asymptomatic urinary abnormalities
In this condition, significant proteinuria (ranging from 150mg to 3.5g/day), hematuria or pyuria occur in an asymptomatic individual. Since many illnesses may start as asymptomatic urinary abnormalities, these findings should not be brushed aside. It may be possible to detect renal or systemic diseases even at this stage by proper investigation.
Acute renal failure
This condition is characterized by acute deterioration of renal function, often but not invariably associated with oliguira.
Chronic renal failure
It is characterized by persistent reduction of renal function for at least 6 months and is caused by irreversible nephron loss.
Urinary tract infection
It is characterized by excretion of pus and significant numbers of pathogenic bacteria in urine (more than 105 colonies/ml), and associated with symptoms referable to upper or lower urinary tract.
Urinary Tract obstruction
Ureteric obstruction leads to ipsilateral renal pain and the development of hydronephrosis. Lower urinary obstruction is characterized by thin urine stream or total block resulting in retention of urine.
Renal tubular defects
Anatomical defect of renal tubules manifests as cysts of various types and are often diagnosed by intravenous urography. Functional disorders are characterized by abnormalities in one or more of the tubular functions.
Renal diseases account for the major proportion of secondary hypertension.
It is the presence of calculi in the Kidneys or the urinary passages. It is characterized by the combination of renal colic with hematuria, presence of stones in urine or radiological visualization of the stone.
All the medical renal disorders fall into one of ten different clinical syndromes. Assignment to these syndromes can be done by clinical and preliminrary laboratory criteria. These clinical syndromes may result from different etiological factors and therefore it should be the endeavour to identify the case in each case.
© 2014 Funom Theophilus Makama