Unit 3: Renal calculi and CSF analysis
Clinical Biochemistry-II notes · PTU syllabus (BMLS505-18)
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Unit summary
Kidney stones and cerebrospinal fluid both reveal disease through chemistry. This unit covers the qualitative analysis of renal calculi and the chemical examination of CSF.
After this unit you can
- Classify renal calculi
- Perform qualitative chemical analysis of stones
- Collect and handle CSF correctly
- Perform and interpret chemical examination of CSF
PTU syllabus topics
Qualitative analysis of renal calculi, chemical examination of cerebrospinal fluid
Appearance
Clear
Turbid
Cells
0–5 lymphocytes/µL
Many neutrophils
Protein
15–45 mg/dL
Raised
Glucose
About 60% of blood glucose
Low
Topic 1
Renal calculi
Calcium oxalate
Hard, dark, spiky (mulberry) — commonest
Hypercalciuria, hyperoxaluria, low fluid intake
Calcium phosphate
Pale, may form staghorn
Alkaline urine, hyperparathyroidism
Magnesium ammonium phosphate (struvite, triple phosphate)
Large staghorn stones
Urease-producing infections (Proteus)
Uric acid
Smooth, yellow–brown; radiolucent
Gout, acid urine, tumour lysis
Cystine
Waxy, yellow; hexagonal crystals
Cystinuria (inherited)
Topic 2
Qualitative analysis of renal calculi
- 1Wash, dry and describe the stone (size, shape, colour, surface)
- 2Powder it and dissolve in dilute HCl (note effervescence for carbonate)
- 3Carry out chemical tests on the solution
- 4Report the composition
Calcium
Ammonium oxalate after neutralising
White precipitate
Oxalate
Dissolve in acid; potassium permanganate decolourised
Decolourisation
Phosphate
Ammonium molybdate with nitric acid
Yellow precipitate
Ammonium
Nessler's reagent or heat with NaOH
Brown colour or ammonia smell
Magnesium
Titan yellow in alkali
Red colour
Carbonate
Effervescence with HCl
Bubbles of CO₂
Uric acid
Murexide test (nitric acid, evaporate, add ammonia)
Purple colour
Cystine
Sodium nitroprusside after cyanide reduction
Magenta–red colour
- Infrared spectroscopy and X-ray diffraction are the accurate reference methods.
Topic 3
Collection and handling of CSF
- Collected by lumbar puncture (L3–L4 or L4–L5) under aseptic conditions into three or four sterile tubes: tube 1 for chemistry, tube 2 for microbiology, tube 3 for cell counts (least blood contamination). Examine immediately — cells lyse and glucose falls with delay. Collect a blood glucose sample at the same time.
Topic 4
Chemical examination of CSF
Protein
15–45 mg/dL (lumbar)
High in bacterial and tuberculous meningitis, Guillain–Barré syndrome (with normal cells), tumours, haemorrhage
Glucose
50–80 mg/dL; about 60% of blood glucose
Low in bacterial, tuberculous and fungal meningitis
Chloride
120–130 mmol/L
Low in tuberculous meningitis (older marker)
Lactate
Below 2.5 mmol/L
High in bacterial meningitis
ADA
Low
Raised in tuberculous meningitis
Globulins
Pandy's test negative
Positive (turbidity with phenol) in raised globulins
- Pandy's test
- 1 drop CSF in saturated phenol — bluish-white turbidity indicates raised globulins
- Nonne–Apelt test
- Ammonium sulphate ring for globulins
- Quantitative
- Turbidimetry (sulphosalicylic acid or TCA) or pyrogallol red dye binding
- Oligoclonal bands
- Isoelectric focusing — multiple sclerosis
- Xanthochromia: yellow supernatant from bilirubin after subarachnoid haemorrhage (12 hours or more), high protein or jaundice; distinguishes true haemorrhage from a traumatic tap.
Key terms
- Struvite
- Magnesium ammonium phosphate stone linked to infection
- Murexide test
- Colour test for uric acid
- Lumbar puncture
- Procedure for collecting CSF
- Pandy's test
- Phenol test for CSF globulins
- Xanthochromia
- Yellow colour of CSF from blood breakdown
Quick revision
- Stone types and associations.
- Stone analysis steps; tests for calcium, oxalate, phosphate, ammonium, magnesium, carbonate, uric acid, cystine; IR spectroscopy.
- CSF collection tubes; urgency; paired blood glucose.
- CSF protein, glucose, chloride, lactate, ADA; Pandy's test; xanthochromia.
Important exam questions
Practice questions written to the PTU exam pattern for this unit's syllabus: short answers (Section A style) and long answers (Sections B and C style).
Short-answer questions
- Q1.Name the commonest type of kidney stone.
- Q2.Which infection causes struvite stones?
- Q3.Describe the murexide test.
- Q4.Why must CSF be examined immediately?
- Q5.Give the normal CSF glucose.
- Q6.What is xanthochromia?
Long-answer questions
- Q1.Describe the types of renal calculi and their qualitative analysis.
- Q2.Describe the chemical examination of CSF and its interpretation in meningitis.
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