Urine analysis | Microscopic examination of urine sample, interpretation of results

In this article, we are going to discuss the interpretation and significance of the data found in a urine analysis report regarding the microscopic examination of urine sample which includes the Pus cells, R.B.Cs, casts and urine crystals .Also, interpretation of the results and causes of increase or decrease of its values is discussed.
* Physical examination and Chemistry of Urine analysis has been discussed before .
A- Pus cells = dead WBCs
 (Normally up to 4/ H.P.F.)
• If  >4/ H.P.F = pyuria, it is significant if  > 10/ H.P.F.
Pyuria indicates an inflammatory reaction within the urinary tract.
• So if pyuria + ve, Culture of mid stream urine sample is indicated :

==> +ve Culture (Bacterial growth) ==> According to the Bacterial Count :
> 100.000/mm = Infection.
• 10.000 - 100.000 ==> suspicion of infection, to be reported
< 10.000 = may be due to contamination .

==> -ve Culture  (Sterile Pyuria) :
1- Urinary tract infection in patient under antibiotic.
2- TB.
3- Renal stones.
4- Graft rejection.
5- Glomerulonephritis.
6- Drug induced interstitial nephrltls.
7- Non gonococcal urethritis caused by mycoplasma chlamydia .

• Drug induced interstitial nephritis e.g. methicillin, penicillins, cephalosporins, sulfonamides, rifampicin ===> Hypersensitivity ===> eosinophiluria.
• It is important to use the morning mid stream urine samples for microscopic examination.
• Recently the bacterial count is modified according to certain situations e.g.. in diabetics, pregnant females, presence of urinary catheter or immunocompromized patient.

B- R.B.Cs

 Normally up to 5/ H.P.F.
If  > 5 = Haematuria
Causes of Haematuria :

C- Casts 
• Microscopic cylindrical structures due to coagulation of tubular protein (Tamm-Horsfall proteins) + albumin ± cellular element formed within kidney tubules.
• Because they are formed inside the tubules, they indicate upper urinary tract lesion (inside the kidneys.) i.e. within the nephrons.
• Any excessive cells or ++ albumin in urine ==> coagulation of tubular Protein ==> cast formation.
• The name of the cast may refer to its cellular element.
• The presence of red or white blood cells in the casts gives evidence of inflammatory parenchymal renal diseases.
• Casts may contain cellular material (RBCs, WBCs, tubular 'cells), lipids, fibrin, bile and crystals.

1- R.B.Cs- casts 
(Indicates acute glomerulonephritis)
Inflammation of glomeruli leads to ++ RBCs + albumin + coagulation of tubular protein) ===>  RBCs cast.

2- W.B.Cs casts 
(indicates pyelonephritis in a patient with urinary tract infection), also present in interstitial nephritis.
Inflammation ==>  tubular protein coagulation + WBCs  ===>  WBCs cast.

3- Tubular cell cast and Granular casts
• Both casts consist of (Coagulation of tubular protein + degenerated or necrosed tubular cells).
• If casts remain in the kidney for a short period they appear as tubular cell casts, if the casts remain in the kidney for long time the cells are partly degraded to form coarse granular casts.
• Tubular casts or coarse granular cast in a patient with acute renal failure help to make the diagnosis of acute tubular necrosis.
• Coarse granular casts may present in chronic parenchymal diseases as chronic glomerulonephritis or chronic Interstitial nephritis .

4- Hyaline casts     (Nephrotic syndrome)
• Hyaline cast is sometimes normal in urine.
• Tubular protein + albumin ===> Hyaline cast (no cellular element).

5- Fatty (Lipid) casts    
• Tubular protein + albumin + lipiduria.
• Common in nephrotic $.

6- Broad casts
• Cast formed in dilated kidney tubules in C.R.F.

7- Crystal casts
• In patients who are taking triametrene and also cases of hypercalcemia or hyperuricosuria.

D- Urine Crystals 
• In the absence of specific symptoms crystals of calcium oxalate and uric acid are of little clinical significance
1- Uric acid present in acidic urine, acute uric acid nephropathy and hyperuricosuria.
2- Calcium phosphate, in alkaline urine.
3- Calcium oxalate, in acidic urine and hyperoxaluria.
4- Cystine, in cystinuria.

Read also :
Urine Analysis Physical examination,  interpretation and significance
Urine Analysis | Urinary proteins (chemistry) , causes of Proteinuria
Urine analysis | Microscopic examination of urine sample, interpretation of results
Dr.Tamer Mobarak


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