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Kidney Function Test

Hematuria (Ref. Hari. 18th ed., pg - 339)
  1. Glomerular hematuria: It should be suspected in the presence of
    1. Dysmorphic (crenated) urinary erythrocytes
    2. Presence of RBC castsQ
    3. Concomitant proteinuriaQ (> 1 gm/day)
  2. Non glomerular hematuria: It is characterized by the presence of
    1. Isomorphic urinary erythrocytes
    2. Absence of RBC casts
    3. No significant proteinuria.
  1. Normally ≤ 3 RBC/mm3 may be seen in an uncentrifuged urine sample or up to 1 RBC/ HPF in a centrifuged urine sample. 
  2. RBCs present in excess of the above number indicates hematuria.
  3. >100 RBC/HPF = Gross hematuria
Causes of hematuria
  1. Renal
    1. Glomerular disease
    2. Carcinoma (renal cellQ, transitional)
    3. Cystic disease (polycystic diseaseQ, medullary sponge kidney)
  2. Extra – renal
    1. Calculi, Infection, Neoplasm, Prostatitis, Trauma, Urethritis,
    2. Bladder – catheterization, Post – cyclophosphamide.
  3. Systemic
    1. Coagulation disorders (including anticoagulant drugs)
    2. Sickle cell trait or disease
    3. Vasculitis
Recurrent hematuria-
  1. IgA nephropathyQ
  2. Alport syndromeQ
  3. TumourQ
Important Points:

Urine darkens on standing in (PGI June 2008)

  1. PorphyriaQ
  2. MelanomaQ
  3. AlkaptonuriaQ

Urine may be coloured red in the presence of hemoglobin, myoglobin, drugs (e.g. rifampicin), beetroot ingestion and porphyria. In these cases RBCs are absent in urine.


Extra Edge
  1. In a case of hematuria, to get a diagnosis USG is the best initial investigation. 
  2. Urine microscopic examination will tell only whether hematuria is there or not. It may not tell the exact diagnosis of the cause. 
  3. X-ray KUB is useful only for renal stone. It is of no use for any other cause of hematuria. 
  4. DTPA scan is useful to estimate GFR. It is of no use to tell about the cause of hematuria.
Acanthocyte are a form of RBC with spikes on it.
Seen in, 
  1. Abetalipoproteinemia,
  2. Liver disease,
  3. Neuroacanthocytosis.


Urinary Casts (Ref. Hari. 18th ed., Pg - 339)
Casts are formed from Tomm – Horsfall glycoproteinQ, which is synthesized and secreted in the ascending limb of the loop of HenleQ. The Tamm – Horsfall protein along with cellular elements forms the cast in acid medium.
  1. Physiologic casts
    1. Hyaline castsQ are transparent and cylindrical, and are seen in the urine of normal subjects.
    2. Granular casts not specificQ are semitransparent cylinders with refractile granules of uncertain origin.
  2. Pathological casts: Casts may contain cellular material (erythrocytes, leukocytes, tubular cells, bacteria of fungi), fibrin, lipids, bile and/or crystals.
Significance of specific urinary casts
  Type Significance
1. Red cell casts GlomerulonephritisQ
2. White cell casts PyelonephritisQ, interstitial nephritis (indicative of infection or inflammation)
3. Broad, waxy cast Chronic renal failureQ
4. Muddy Brown ARF
Significance of bacteria in UTI
  1. Determination of the number and type of bacteria in the urine is an extremely important diagnostic procedure.
    The detection of bacteria in a urine culture is the diagnostic "gold standard" for UTI;
  2. In symptomatic patients, bacteria are usually present in the urine in large numbers (≥105/mL). 
  3. The presence of bacteriuria of any degree in suprapubic aspirates or of ≥102 bacteria/ml of urine obtained by catheterization usually indicates infection. 
  4. Microscopic bacteriuria, which is best assessed with Gram-stained uncentrifuged urine, is found in >90% of specimens from patients whose infections are associated with colony counts of at least 105/ml, and this finding is very specific. 
  5. The leukocyte esterase "dipstick" method is less sensitive than microscopy in identifying pyuria but is a useful alternative when microscopy is not feasible. 
Important Points

Leukocytes in Urine

  1. An increase in the leukocyte count in the urine most commonly implies infection.
  2. If number of WBCs in uncentrifugedQ midstream urine in women is >10/ml, it is abnormal If 3-10/ml, then it is of doubtful significance.
  3. If number of WBCs in uncentrifuged midstream urine in men is > 3/ml, it is abnormal.
  4. If the number of WBCs in centrifuged midstream urine both men and women is > 5 WBCs/HPF, it is abnormal
  5. When pyuria is present without bacteria (sterile pyuria), three-fourth of the patients show an underlying urinary tract abnormality.

Cause of non infective (Sterile pyuria) WBCs in urine

  1. C. trachomatis,
  2. U. urealyticum,
  3. M. tuberculosis
  4. Fungi
  5. Calculi
  6. Nephrocalcinosis,
  7. Vesicoureteral reflux
  8. interstitial nephritis
  9. Polycystic disease.

  1. Large bizarre crystals of any type including calcium oxalate and uric acid usually indicate increased urinary excretion and may indicate calculus disease.
  2. Cystine crystals are always abnormal and indicate cystinuria. (MCQ)
Proteinuria (Ref. Hari. 18th ed., Pg - 273, 338)
Urine protein composition (total up to 150 mg/day in adults)
Tamm – Horsfall protein 70 mgQ
Albumin 30 mgQ
Selective proteinuriaQ
Minimal change disease in children produces selective proteinuriaQ. Because of lower molecular weight there is selective excretion of albumin in urine.
Glomerular proteinuria is associated with albumin > Globulin
Feature Glomerular proteinuria Tubular proteinuria
Total protein excretion /day Usually > 2.0 g/day
Proteinuria may reach nephrotic range > 3.5 g/day
Usually < 2.0 g/day
Proteinuria never reaches nephrotic range.
Protein type · Proteinuria chiefly consists of albumin
· Albumin is usually greater than globulins (Albumin > Globulin)
· Low molecular weight proteinuria is the hallmark of tubular proteinuria.
· Proteinuria chiefly consists of Low molecular weight proteins (alpha and beta microglobulins). Albumin is invariably present (Globulin > albumin)
Albumin/beta2 microglobulin ratio Usually exceeds 1000:1 Usually less than 10:1
Tamm Horsfall protein Tamm Horsfall proteins are not increased as there is no injury to tubular cells Tom Horsfall protein secretion may be increased by injured tubular cells of ascending loop of Henle i.e & distal tubule.
- N Acetyl glucosamine
- Lysozyme
Normal May be increased (Increased in case of tubular cell injury)


Important Points

Raised level of serum beta 2 microglobulin is seen in multiple myeloma

Microalbuminuria (AIIMS Nov 2010)
  1. This indicates a daily excretion of albumin in the range of 30 – 300 mg/dayQ.
  2. It occurs in diabetes mellitus with early renal involvement
  1. Dipstick testing detects only albumin at concentration more than 250 mg/LQ
  2. False – positive dipstick results for proteinuria are seen when
    1. Urine pH is ≥8Q,
    2. Penicillins,
    3. Aspirin
    4. Oral hypoglycemic agents.
Bence Jones protein
  1. A Bence Jones protein is a monoclonal gamma globulin protein found in the blood or urine. 
  2. Found in multiple myeloma.
    The proteins are immunoglobulin light chains (paraproteins) and are produced by neoplastic plasma cells. They can be kappa (most of the time) or lambda. 
  3. The light chains can be detected by heating or electrophoresis of concentrated urine. Light chains precipitate when heated to 50-60 degrees C and redisolve at 90-100 degrees C.
    Bence Jones proteins don't react with the reagents normally utilized in urinalysis dipsticks. 
Other Types Of Proteinuria
  1. Benign orthostatic proteinuria is typically found in tall adolescents. (PGI Nov 2010)
    Protein is found in the urine collected during the day time after the patient has been ambulant, but not in the overnight specimen collected immediately on rising in the morning (i.e. first morning urine sample does not contain protein. It is a Benign condition, It resolves spontaneously. No investigation and no treatment required.  
  2. Transient proteinuria may be associated with conditions like cardiac failure, fever, or heavy exerciseQ. It disappears within hours after cessation of exercise and with resolution of the disease process. Proteinuria after marathon running may be as a heavy as 5 gm per liter of urine. 
Blood Urea Nitrogen (BUN) normal range 7-20 mg% (Ref. Hari. 18th ed., pg –3596) 
  1. Increased BUN-
    1. Reduced effective circulating blood volume (prerenal azotemia)
    2. Catabolic states
    3. High-proteinQ diets
    4. GI bleeding
    5. Glucocorticoids
    6. TetracyclineQ
  2. Decreased BUN
    1. Liver diseaseQ (AIPG 10)
    2. MalnutritionQ
    3. Sickle cell anemiaQ
Serum Creatinine (Normal range 0.5-1.2 mg//ml, (Ref. Hari. 18th ed., pg – 3596)
  1. Creatinine is produced by the nonenzymatic dehydration of muscle creatine. 
  2. Because the daily production of creatinine is relatively constant, its clearance is a relatively reliable index of GFR.
  3. In people having highly muscular body have more creatinine and people with thin muscle body have low creatinine.
Important Points

Creatinine clearance rate (CCr or CrCl) is the volume of plasma that is cleared of creatinine per unit time and is a useful measure for approximating the GFR. (Ref. Hari. 18th Ed., pg - 334)

  1. Creatinine clearance, is measured from plasma and urinary creatinine excretion rates for a defined time period (usually 24 h) and is expressed in milliliters per minute: CrCl = (Uvol x UCr)/(PCr x Tmin).
  2. Creatinine clearance is useful for estimating GFR.
  3. Two formulas are used widely to estimate kidney function from serum creatinine: (1) Cockcroft-Gault and (2) four-variable MDRD (Modification of Diet in Renal Disease).

Cockcroft-Gault: CrCl (mL/min) = (140 – age (years) x weight (kg) x [0.85 if female])/(72 x sCr (mg/dL)


MDRD: eGFR (mL/min per 1.73 m2) = 186.3 x PCr (e–1.154) x age (e–0.203) x (0.742 if female) x (1.21 if black)


Imaging studies:
  1. Radionuclide Studies- Radionuclide studies can measure renal function.
    1. Technetium diethylenetriamine pentaacetic acid (99mTc – DTPA) (dynamic renal scan) is freely filtered by the glomerulus and not reabsorbed and is used to estimate GFRQ.
    2. Technetium dimercaptosuccinate (99mTc – DMSA) (State renal scan) is bound to the tubules and provides an assessment of functional renal mass.
    3. Radioiodinated (131I) orthoiodohippurate is secreted into the renal tubules and assesses renal plasma flow (RPF).
Extra Edge
  1. Kidney size can be determined; a kidney less than 9 cm in length indicates significant irreversible renal disease.Q
  2. A difference in size of more than 1.5 cm between the two kidneys is observed in unilateral renal disease.
Intravenous Urography (IVP)
Rapid sequence IVP is done for Renal artery stenosis


Important Points

Renal Biopsy


Indications include

  1. Acute renal failure which is unresolving and for which a cause is not evident;
  2. Nephrotic syndrome if one suspects a primary glomerular disease;
  3. Proteinuria of 2 g/24h/1.73 m2 along with an abnormal urine sediment with or without functional deterioration;
  4. Hematuria associated with an abnormal urine sediment or proteinuria;
  5. Systemic diseases associated with kidney dysfunction, such as systemic lupus erythematosus, Goodpasture’s syndrome, and Wegener’s syndrome, to confirm the extent of renal involvement and to guide management;
  6. Suspected transplant rejection, to differentiate it from other causes of acute renal failure and to guide management.
Contraindications include:
  1. A solitary or ectopic kidney (exception: transplant allograftsQ),
  2. Horseshoe kidneyQ
  3. Uncorrected bleeding disorder,
  4. Severe uncontrolled hypertension,
  5. Renal infection,
  6. Renal neoplasm,
  7. Hydronephrosis,
  8. End–stage kidneys,
  9. Congenital anomalies

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