This article covers important clinical findings of urological and renal conditions, including changes in micturition (e.g., dysuria, anuria) and changes in urine (e.g., hematuria, proteinuria) as well as the routine diagnostics for the initial evaluation of patients with urological and renal symptoms, including urinalysis and renal function testing. Urinalysis helps to evaluate urinary abnormalities and involves gross assessment of urine, dipstick, and microscopy of urine sediment. Dipstick is a diagnostic tool consisting of a urine test strip that allows for quick assessment of potentially pathological changes of various parameters (e.g., pH, glucose, protein). Urine sediment allows for microscopic detection of cells, urinary casts, urinary crystals, bacteria, and yeast in a urine sample. Renal function testing involves a panel of parameters to assess for renal dysfunction. Inulin clearance and creatinine clearance provide the most accurate calculation of the GFR while serum creatinine can be used together with demographic data to provide an estimated GFR. The BUN/creatinine ratio and fractional excretion of sodium can be used to evaluate the cause of acute kidney injury. The findings of these tests may be diagnostic or provide guidance for further diagnostic evaluation (e.g., renal biopsy, imaging)
For more on imaging and urodynamic tests, see “ .” For more on urine culture, see “Laboratory tests” under diagnostics in “ .” Current NBME laboratory reference values can be found under “Tips and Links” below.”
History and physical examination
- Changes in urine and micturition: evaluate amount, frequency, appearance, and discomfort (see table below for details)
- Flank pain
- Costovertebral angle tenderness: : characteristic of pyelonephritis
- Nausea/vomiting: can be a sign of end-stage renal disease: or urolithiasis
- Hypertension: : can be an extrarenal manifestation of kidney injury
- Peripheral : : See “.”
- Pericardial friction rub: : See “.”
- Pulmonary edema: can indicate volume overload due to renal injury with low urine output
- Skin changes: can be indicative of an underlying systemic disease
Changes in micturition
|Overview of micturition changes|
|Quality of micturition|
|Dysuria|| || |
|Quantity of urine excretion|
Changes in urine
|Overview of urine changes|
|Glycosuria|| || |
Urinalysis involves the gross examination of urine, chemical evaluation using urine dipstick, and microscopic assessment of urine sediment. Further tests include and urinary electrolyte levels. Indications for urinalysis include renal, urinary, and metabolic conditions.
Gross urine assessment
- Urine color
- Turbidity: (cloudiness of the urine): cloudy urine suggests infection or chyluria
A diagnostic tool consisting of a urine test strip that allows for quick assessment of potentially pathological changes of various parameters.
- pH (urine pH usually ranges from 4.5–8)
- Urine specific gravity: Measures the ratio of urine density over pure water density (normally 1.005–1.030)
- Heme: > 90% sensitivity for hematuria (low specificity)
- Leukocyte esterase: : enzyme produced by WBC that indicates a urinary tract infection
- Protein (albumin): See “.”
- Glucose: glycosuria is a key finding of
- Ketones: ketonuria can help diagnose , a complication of
- : See “” and “.”
- Nitrite: : indicative of urinary tract infection caused by gram-negative bacteria (e.g., Enterobacteriaceae)
- Indications: can help identify acute and chronic kidney diseases, classify renal calculi, and diagnose UTIs
- Method: Urine is centrifuged and the pellets are examined under the microscope (supernatant is discarded).
- Assessment: provides valuable information about the underlying cause of kidney damage
|Urinary casts |
|Hyaline casts|| || || |
|Granular casts|| || |
|Muddy brown casts|| || |
|Hemoglobin casts|| || || |
|Fatty casts|| || || |
|Renal tubular epithelial cell casts|| |
|White blood cell casts|| |
|Red blood cell casts|| |
|Waxy casts|| || |
|Broad casts|| || || |
Further laboratory tests
- Urine osmolality
- Urine osmolar gap (UOG): The difference between measured urine osmolality and calculated urine osmolality, used to estimate urine NH4+ concentration in metabolic acidosis.
- Urine electrolytes
- Urine creatinine: used to calculate
- : see diagnosis of
- Parameters of renal function allow for the evaluation of changes in renal function.
- Inulin clearance and creatinine clearance (with 24-hour urine collection): allow for the most accurate calculation of the glomerular filtration rate
- Serum creatinine and serum cystatin C allow for indirect measurement of the glomerular filtration rate (see ).
- Urea (BUN) and uric acid are largely dependent on renal excretion; however, they only provide an inaccurate assessment of renal function.
- Fractional excretion of urine is used to establish the cause of acute kidney injury.
- Current NBME laboratory reference values can be found under “Tips and Links” below.”
Glomerular filtration rate (GFR) 
- Defined as the 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
- 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 10 years.
- GFR can be calculated or estimated using various methods (e.g., estimated GFR).
- Indirect indicator of renal function
- Creatinine-blind range
- Additional interfering factors:
Serum creatinine levels do not start rising until the GFR is reduced by approx. 50%.
- Used in clinical settings to approximate the glomerular filtration rate (GFR)
- Slightly overestimates GFR because of minimal creatinine secretion in the proximal tubules 
- A precise evaluation of creatinine clearance requires measuring creatinine in the urine over a 24-hour period.
- Creatinine clearance = (CreaUrine x V) / CreaPlasma ≈ GFR
Creatinine clearance can be used to approximate the GFR.
- Calculated using serum creatinine concentration and demographic data
- Several prediction equations can be used in clinical practice.
Serum cystatin C
- A more precise indicator of the GFR than serum creatinine
- Cystatin C is a small protein that inhibits cysteine proteinases and is produced by all nucleated cells.
- Analysis is more complex and expensive; therefore, not routinely ordered.
- Lower “blind range” than serum creatinine: used particularly when urine sampling is not feasible (e.g., in infants)
Blood urea nitrogen (BUN)
- A waste product produced by the liver in the urea cycle after protein degradation
- Filtered and excreted by the kidneys
- Elevated with
- Reduced GFR
- High protein diet
- Can help diagnose the underlying cause in acute kidney injury
Fractional excretion of sodium (FeNa)
- Definition: percentage of the glomerular filtered sodium (NaFiltered) that is eventually excreted in the urine (NaExcreted)
- Filtered Na = NaPlasma x GFR
- Excretion rate of Na = NaUrine x V
- FeNa = NaExcreted / NaFiltered
- FeNa = (NaUrine x V) / (NaPlasma x GFR)
- FeNa = (NaUrine x V) / (NaPlasmax [CreaUrine x V / CreaPlasma])
- FeNa = (NaUrine x CreaPlasma) / (NaPlasmax CreaUrine)
In acute kidney injury
- Low FeNa (< 1%): indicates a prerenal cause (renal hypoperfusion)
- High FeNa (> 2%): indicates an intrarenal etiology (e.g., acute tubular necrosis)
- Inconclusive FeNa (1–2%): can be seen with either disorder
- In hypotonic hyponatremia
- Low FeNa (< 1%): extrarenal cause
- High FeNa (> 1%): renal cause
- In acute kidney injury
Additional blood tests
- Autoantibodies: : particularly antinuclear antibodies (ANCA) as an indication of glomerulonephritis
- Uric acid: a metabolite of purine bases
Other parameters that should be evaluated in renal disease (particularly in chronic renal failure) are serum electrolytes (Na+, K+, Ca2+, phosphate), vitamin D, and parathyroid hormone (PTH).
- See the Diagnostics section of for details.
Renal parameter changes
|Overview of renal parameters|
|Laboratory parameter|| |
Causes of increased values
|Causes of decreased values|
|Cystatin C|| |
|Blood urea nitrogen (BUN)|| |
- Usually performed percutaneously under local anesthesia and with ultrasound guidance.
- Examination of the tissue sample includes light, immunofluorescence, and electron microscopy.
- The most common complication is bleeding.
- Nephritic and/or nephrotic syndrome with no apparent underlying disease: allows diagnosing type of glomerulonephritis
- Suspected lupus nephritis
- Rapidly progressive glomerulonephritis
- Renal transplant rejection or dysfunction
- Unexplained acute kidney injury
- Solitary kidney (relative contraindication)
- Infection of the kidneys
- Coagulation disorders (e.g., thrombocytopenia, disorders of the platelet function, bleeding diathesis)
- Uncontrolled hypertension
- Anatomic abnormalities
- Multiple, bilateral renal cysts
- Renal tumor
- One-Minute Telegram 14-2020-3/3: GFR formulas are just estimates, but can we estimate better?
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