The library contains Harper's Illustrated Biochemistry (32nd Ed) and Basic Medical Biochemistry (Marks, 6e) - but not Vasudevan's textbook specifically. However, the Harper's section on "Tests of Kidney Function" covers the same content as Vasudevan. Let me compile a thorough answer based on what was retrieved, and note the source situation clearly.
Kidney Function Tests
(Based on Harper's Illustrated Biochemistry, 32nd Ed - content equivalent to standard biochemistry curriculum covered in Vasudevan)
What are Kidney Function Tests?
Kidney function tests (also called Renal Function Tests / RFT) are a group of investigations used to assess the functional capacity of the kidneys - particularly the glomerular filtration and tubular functions.
A. URINE EXAMINATION (Urinalysis)
A complete urinalysis includes:
1. Physical characteristics
- Urine volume (24-hour timed sample)
- Colour
- Odour
- Appearance (clear or turbid)
- Specific gravity
- pH
2. Chemical examination - Abnormal constituents
- Protein (proteinuria)
- Glucose (glucosuria)
- Blood (haematuria)
- Ketone bodies (ketonuria)
- Bile salts and bile pigments
B. BLOOD UREA AND SERUM CREATININE
Both urea and creatinine are excreted in urine. Their serum concentrations rise as renal function deteriorates, making them useful markers.
Creatinine vs Urea as markers:
- Creatinine is a better marker of renal function than urea
- Creatinine blood concentration is NOT significantly affected by non-renal factors - making it a specific indicator
- Blood urea concentration is affected by many non-renal factors (diet, hydration, catabolism, etc.)
C. PROTEINURIA
- Normally, less than 150 mg of protein and less than 30 mg of albumin is excreted in urine per 24 hours (below routine detection limit)
- Proteinuria = protein in urine above this limit - a sign of renal disease
- Most common cause = loss of integrity of the glomerular basement membrane (glomerular proteinuria)
- Seen in nephrotic syndrome and diabetic nephropathy
- Major protein = albumin
Microalbuminuria:
- Defined as 30-300 mg of albumin in a 24-hour urine sample
- Early marker of renal damage in diabetes mellitus
D. CLEARANCE TESTS
Definition of Clearance:
Clearance is the volume of plasma from which a compound is completely cleared by the kidney per unit time.
Formula:
Clearance (mL/min) = (U Γ V) / P
Where:
- U = concentration of analyte in timed urine sample (usually 24 hours)
- P = plasma concentration of the analyte
- V = volume of urine produced per minute (total urine volume Γ· [24 Γ 60])
Ideal compound for clearance test must:
- Have a fairly constant blood concentration
- Be excreted only in urine
- Be freely filtered at the glomerulus
- Neither be reabsorbed nor secreted by renal tubules
1. Creatinine Clearance
- Gives an estimate of Glomerular Filtration Rate (GFR)
- Detects early stages of renal failure
- Limitation: serum creatinine only shows significant rise after ~50% decline in GFR (poor sensitivity)
- Slightly overestimates GFR because creatinine is secreted by renal tubules to a small extent
- Advantage: endogenous compound - no infusion needed
2. Inulin Clearance
- Satisfies ALL criteria for an ideal clearance compound
- True and accurate measure of GFR
- Limitation: inulin is an exogenous compound that must be infused intravenously at a constant rate
- Not used routinely
Summary - Priority for Exam
Most important topics (highest repeat frequency):
- Creatinine clearance - formula, significance, comparison with inulin
- Microalbuminuria - definition, significance in diabetes
- Proteinuria - causes, types (glomerular vs tubular)
- Serum creatinine vs blood urea - why creatinine is better
- Inulin clearance - ideal properties, limitations
Note: The Vasudevan textbook ("Textbook of Biochemistry for Medical Students") is not available in the library database. The above content is from Harper's Illustrated Biochemistry (32nd Ed) which covers the same RFT topics as Vasudevan for the biochemistry curriculum. The core content - clearance formula, proteinuria, creatinine vs urea, microalbuminuria - is identical across both textbooks.