Pathology
Clinical Pathology
Clinical pathology for MBBS and NEET-PG: urinalysis with casts, and cerebrospinal, pleural, peritoneal and synovial fluid analysis, mapped to NMC codes PA23.1 to PA23.3.
MedNext Academy | 3 min read
Clinical Pathology
Clinical pathology for MBBS and NEET-PG: urinalysis with casts, and cerebrospinal, pleural, peritoneal and synovial fluid analysis, mapped to NMC codes PA23.1 to PA23.3.
This chapter covers laboratory analysis of body fluids in routine clinical pathology. It details urinalysis with its physical, chemical and microscopic components, and the interpretation of cerebrospinal, pleural, peritoneal and synovial fluids, which are frequently examined and tested.
High-yield: Clinical Pathology
- Urinalysis has three parts: physical examination, chemical (dipstick) testing and microscopy of the sediment.
- The dipstick detects albumin but is insensitive to Bence Jones (light chain) proteinuria, which needs electrophoresis.
- Red cell casts in the urine indicate a glomerular source of bleeding, as in glomerulonephritis.
- White cell casts point to pyelonephritis or interstitial nephritis.
- Granular and waxy casts are seen in chronic renal disease, and hyaline casts can be normal.
- Glycosuria without hyperglycaemia suggests renal glucosuria, while glycosuria with hyperglycaemia suggests diabetes mellitus.
- Ketonuria is seen in diabetic ketoacidosis and in starvation.
- Cerebrospinal fluid in bacterial meningitis shows raised neutrophils, high protein and low glucose.
- Cerebrospinal fluid in viral meningitis shows raised lymphocytes, mildly raised protein and normal glucose.
- Tuberculous meningitis shows lymphocytes, high protein, low glucose and a fibrin web on standing.
- A pleural effusion is separated into transudate and exudate using Light criteria based on protein and lactate dehydrogenase ratios.
- A transudate is protein-poor and follows altered pressures, while an exudate is protein-rich and follows inflammation or malignancy.
- Synovial fluid analysis distinguishes gout (negatively birefringent urate crystals) from pseudogout (positively birefringent calcium pyrophosphate crystals).
- A high specific gravity indicates concentrated urine, while a fixed low specific gravity suggests impaired concentrating ability.
Cerebrospinal fluid patterns
- **Bacterial meningitis:** Neutrophils high, protein high, glucose low.
- **Viral meningitis:** Lymphocytes high, protein slightly high, glucose normal.
- **Tuberculous meningitis:** Lymphocytes, protein high, glucose low, fibrin web on standing.
- **Urinary casts:** Red cell casts point to glomerulonephritis; white cell casts to pyelonephritis.
NMC competencies in this chapter
- **PA23.1:** Urinalysis: physical examination, chemical tests and microscopy
- **PA23.2:** Body fluid analysis: CSF, pleural, peritoneal and synovial fluid
- **PA23.3:** Interpretation of common clinical pathology specimens and pitfalls
Frequently Asked Questions
What does a urinary red cell cast indicate?
A glomerular source of bleeding, most typically glomerulonephritis, rather than bleeding from the lower urinary tract.
How does cerebrospinal fluid differ in bacterial and viral meningitis?
Bacterial meningitis shows raised neutrophils, high protein and low glucose, while viral meningitis shows raised lymphocytes, mildly raised protein and normal glucose.
How is a pleural effusion classified?
By Light criteria into transudate and exudate, using the ratios of fluid to serum protein and lactate dehydrogenase.
Why can the dipstick miss myeloma proteinuria?
Because the dipstick detects albumin but not free light chains, so Bence Jones proteinuria needs urine electrophoresis to detect.
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