- Clinical science
Diseases of the kidney and the urinary tract can present with a wide array of symptoms. In addition to flank or groin pain, referred pain may occur in other regions of the body, which can make diagnosis difficult. Therefore, acute abdominal pain requires consideration of the kidneys and urinary tract. Most chronic renal diseases are asymptomatic and are only detected through abnormal findings on urinalysis (erythrocytes, protein) or pathological changes of renal function parameters (increased serum creatinine, blood urea nitrogen). An ultrasound can be used for a quick evaluation of the kidney and urinary tract and is critical in diagnosing urinary tract obstructions and urinary retention.
- Changes in micturition (amount, appearance, discomfort)
- Flank pain
- Costovertebral angle tenderness (CVAT)
- Hypertension: extrarenal manifestations that may indicate kidney injury
- : See .
- Quantity of urine
Quality of urine
- Isosthenuria: loss of the ability to concentrate or dilute urine → urine osmolality approaching that of plasma
- Glycosuria: glucose in the urine
- > 150 mg protein/day in the urine:
- Leukocyturia/pyuria: white blood cells in the urine, sometimes with visible cloudiness
- Bacteriuria: ≥ 105 organisms/mL organisms (in midstream collection)
- (see below)
- Hemoglobinuria: hemoglobin in the urine
- Myoglobinuria: myoglobin in the urine
|Most likely diagnosis|
|Bacteriuria||Urinary tract infection|
|Hematuria in the first or last part of micturition||Urethral damage|
|Persistent hematuria||Vesical or supravesical origin|
|Hemoglobinuria||Severe intravascular hemolysis|
|Polyuria||Diabetes mellitus, diabetes insipidus, drinking excessive amounts of water|
- Gross urine assessment
- pH (urine pH usually ranges from 4.5–8)
- Specific gravity; : Large molecules such as glucose or radiocontrast media may increase the urine specific gravity despite a normal urine osmolality.
- Heme: > 90% sensitivity for hematuria; however, always confirm with microscopy for the presence of RBCs, as a dipstick cannot differentiate between hematuria, hemoglobinuria, or myoglobinuria!
- Leukocytes esterase; : enzyme produced by WBC that indicates a UTI
- Protein (albumin)
- Glucose, ketones, urobilinogen
Tubular structures formed in the distal convoluted tubule and collecting duct of the kidneys
Hyaline casts: nonspecific finding; can also be found in healthy individuals, often after exercise
- Structure: consist of a mucoprotein matrix of Tamm-Horsfall proteins
- Microscopy: homogeneous, transparent, and eosinophilic
- Granular casts: caused by degeneration of cells in RBC or WBC casts
- Waxy casts: represent further degeneration of granular casts
- Renal tubular epithelial cell casts; : indication of glomerulonephritis or interstitial nephritis; can occasionally be found in healthy individuals
- White blood cell casts: strong indication of pyelonephritis; however, can also be seen in glomerulonephritis or interstitial nephritis
- Red blood cells casts; : indication of glomerulonephritis
Broad casts: usually seen with advanced chronic kidney disease; formed in dilated tubules with low flow
- Structure: wider casts
- Hyaline casts: nonspecific finding; can also be found in healthy individuals, often after exercise
|Glomerular hematuria||Nonglomerular hematuria|
|Color (macroscopic)||Red, smoky brown, “Coca-Cola”||Red or pink urine|
|RBC morphology||Dysmorphic||Normal (isomorphic)|
|RBC Casts||Sometimes present||Absent|
|Proteinuria||> 500 mg/day||< 500 mg/day|
Serum creatinine: used as an indirect indicator of the glomerular filtration rate
- Serum creatinine levels do not start rising until the GFR is reduced by at least 50% → If the GFR is > 60 mL/min, serum creatinine cannot be used to assess kidney function = "creatinine-blind" range!
- Additional interfering factors:
- Falsely elevated values: high-protein diet, high muscle mass, rigorous exercise
- Falsely decreased values: low muscle mass
- Blood urea nitrogen (BUN): metabolite of ammonia and proteins (also elevated in catabolic states)
- Uric acid: metabolite of purine bases
- Serum cystatin C : a more precise indicator of the glomerular filtration rate, though the analysis is more complex and expensive. Not routinely ordered.
- Serum creatinine: used as an indirect indicator of the glomerular filtration rate
Creatinine clearance: equates approximately to the glomerular filtration rate (GFR)
- A more precise evaluation of creatinine clearance requires measuring creatinine in the urine over a 24-hour period (urine creatinine concentration x urine volume over 24 hours).
Creatinine clearance or GFR can be estimated using the Cockcroft-Gault equation.
- Equation: CCr (mL/min) = ((140-age) x lean body weight(kg)) / (72 x serum creatinine (mg/dL))
- For women, the result should be multiplied by 0.85.
Glomerular filtration rate (GFR): volume of primary urine that is filtrated by the kidneys over a certain amount of time per standardized body surface area (1.73 m2)
- Normal GFR: ≥ 90 mL/min/1.73m2 is considered normal.
- GFR is ∼ 120 mL/min/1.73m2 in young adults, decreases with age, and varies considerably between males and females.
- After the age of 29, a physiological decrease in the GFR of about 10 mL/min/1.73m2 occurs every ten years.
- The GFR can be estimated using the .
- GFR but slightly overestimates it because of minimal creatinine secretion at the proximal tubule. approximates
- Other parameters that should be evaluated in renal disease (particularly in chronic renal failure) are Na+, K+, Ca2+, phosphate, vitamin D, and parathyroid hormone (PTH).
- Autoantibodies (particularly antinuclear antibodies as an indication of glomerulonephritis)
- Evaluation of glomerulonephritis with no apparent underlying disease
- Suspected lupus nephritis; or rapidly progressive glomerulonephritis
- Evaluation of renal transplant rejection
- Anatomic abnormalities: abnormal position of the kidneys, atrophic kidneys, vascular malformations in the kidney region
- Coagulation disorders (thrombocytopenia, disorders of the platelet function, bleeding diathesis)
- Uncontrolled hypertension
- Infection of the kidneys
- Renal tumor
- Solitary kidney (relative contraindication)
- Initial hematuria typically suggests a urethral cause.
- Terminal hematuria suggests damage to the bladder, prostate, or trigonal area.
- Total hematuria suggests damage in the kidneys or ureter.
- Microhematuria: hematuria that is not grossly visible
- Macrohematuria: hematuria that is grossly visible (see also )
- Urinalysis: > 3 erythrocytes/HPF or > 5 erythrocytes/ μL
- If asymptomatic, consider malignancy.
- Coagulation disorder (e.g., )
- Myoglobinuria in professional athletes or crush syndrome
- Medication side effect