Urinalysis

Synonyms

Urine examination; urinalysis; urinalysis; urinalysis; urinalysis;

First describer

Already in the early writings of Hippocrates (460 - 375 B.C.) special importance was attached to urine. At that time, particular attention was paid to colour and contenta, which included nephele (cloud), enaiorema (suspension) and hypostasis (precipitate).

A tenet from the Prognostikon reads:

"Clouds floating in urine are a good sign if they are white, a bad sign if they are black." (Buettner 1991).

A publication on oncological cytology was first written by V. D. Lambl in 1856, who also described Giardia lamblia, the causative agent of Lambliasis, named after him. However, it was the 1945 paper by cytopathologist G. N. Papanicolaou (1883 - 1972) and urologist V. F. Marshall, "Urine sediment smears as a diagnostic procedure in cancer of the urinary tract," that represented the decisive breakthrough in oncologic urine cytology (Rathert 2018).

Fairley and Birch first reported a method for detecting glomerular hematuria in 1982, using a phase microscope to demonstrate typical morphological changes in erythrocytes. They referred to the altered erythrocytes as "dysmorphism" (Kuhlmann 2015).

The central importance of urine diagnostics is also evident in the fact that the glass for urine examination, the so-called matula, was the distinguishing mark of physicians in general in the Middle Ages. Even today, the matula is included in the emblem of the Professional Association of German Urologists (Rathert 2007).

Urinalysis is possible with spontaneous urine as well as with 24 h collected urine.

However, proper preanalytics is of central importance for spontaneous urine testing.

Spontaneous urine:

• Physical exertion

The patient should avoid strenuous physical exertion in the 72 h before the urine sample is taken, otherwise false pathological proteinuria and microhaematuria may occur.

• Morning urine

In the inpatient setting, the 1st morning urine is generally used, in the outpatient setting the 2nd portion of the day. In order to obtain a concentrated urine, the patient should not drink too much beforehand.

• Menstruation

If possible, urine samples should not be used during menstruation in women.

• Midstream urine

After the first portion of urine has been discarded, the so-called midstream urine is collected and used for examination.

Hegele (2015) recommends using midstream urine exclusively in men, using a sterile disposable catheter to collect urine directly from the bladder in women, and suprapubic bladder puncture urine in children.

• Processing

Urine should be processed within a maximum of 2 hours.

(Herold 2021)

24 h Collection urine

The patient should be told exactly how to collect the urine, otherwise the possibility of error is very high. In the USA, for example, professional societies no longer recommend the use of collected urine (Kuhlmann 2015).

• Instructions for collecting urine:

The 1st morning urine should be emptied into the toilet at 8:00 am, then each urine output should be placed into the designated collection vessel, including the 1st urine the other morning at 8:00 am. Following these instructions, it can be expected that 80% will have a credible urine collection (Kuhlmann 2015).

Indications for a collection urine are:

• Nephrolithiasis with determination of
  • Oxalate
  • Magnesium
  • Calcium
  • Uric acid
  • Citrate
  • Phosphate

(Keller 2010)

• Creatinine clearance
• Quantification of proteinuria (standard value 150 mg / d [Kuhlmann 2015])
• in case of a hormonal disease (especially of the adrenal glands)

(Manski 2019)

• Normal values for the 24- h urine:
  • pH: 4.4 - 7.5
  • specific weight 1.010 g / ml - 1.024 g / ml
  • osmolality 500 - 800 mosm / kg
  • Urea 25 g - 35 g / 24 h
  • Uric acid 0.3 g / 24 h - 0.5 g / 24 h
  • Protein < 150 mg / 24 h - 300 mg / 24 h
  • Magnesium 4 mmol / l - 8 mmol / l
  • Calcium < 7.5 mmol / 24 h
  • Uric acid 0.3 g / 24 h - 0.6 g / 24 h
  • Citrate
  • Phosphate

(Manski 2019)

The creatinine- clearance, which allows conclusions about the glomerular filtration rate (GFR), can be calculated from the collected urine according to the following formula:

Cl crea [ml / min] = Ucrea x Uvol divided by Screa x 1440.

(Manski 2019)

There are now numerous laboratory calculators for this on the internet such as.

https://www.wisplinghoff.de/fuer-aerzte/formelsammlung/niere-berechnung-der-endogenen-kreatinin-clearance/

Urinalysis tests include:

• 1. visual and olfactory assessment.

Any discoloration, turbidity of the urine or even odor may be the first indication of an existing infection (Hegele 2015).

• Visual assessment

The intensity of the normal urine color, which is caused by the urochrome content, is proportional to the specific gravity and opposite to the urine volume, i.e.

in the thirst test:

• the urine becomes dark to amber in colour
• the specific gravity rises to a maximum of 1.035 g / l
• there is a high osmolality of up to 1.200 mosm / kg

after water load:

• the urine becomes water light
• the specific gravity decreases to values up to 1.001 g / l
• the osmolality drops down to 50 mosm / kg

(Herold 2021)

Classic exceptions to this are, for example, diabetes mellitus. Here, although a light urine color is found in polyuria, the specific gravity is significantly increased by glucosuria, as well as proteinuria, since proteins have a relatively high specific gravity (Herold 2021).

• Olfactory evaluation
  • sour to fruit-like: e.g. in decompensated diabetes mellitus, ketoacidosis
  • strong smell of meat: in necrotic cell material, pyuria etc.

(Risler 2008)

• 2. test strip examination

With a urine test strip, also called "Stix" in everyday life, the following parameters can be measured:

• 2. a. pH value

Normal value: morning urine 5 - 6, then in the course of the day large fluctuations occur (Manski 2019).

An acidic pH value occurs, for example, in diarrhea, fasting, acidosis, etc., an alkaline, for example, in urinary tract infections.For more details, see urine pH.

• 2. b. Osmolality

The normal value is between 1002 - 1030 mosmol / l.

In antidiuresis osmolality increases to values > 1025 mosmol / l and in water diuresis it is between 1002 - 1010 mosmol / l (Risler 2008).

• 2. c. Leukocytes

Normal value: < 10 µl (Manski 2019).

Leukocyturia is done by detecting granulocyte esterase activity (Risler 2008). Leukocyturia occurs primarily in the presence of a urinary tract infection. If the urine becomes yellow in colour due to the high number of leukocytes, this is known as pyuria.

Leukocyturia in sterile urine can occur in pregnancy, as well as in urethritis, gonorrhea, analgesic nephropathy, urogenital tuberculosis and other diseases.

False positives occur in women in up to 40% due to fluorine (Herold 2021).

• 2. d. Erythrocytes / free hemoglobin:

The physiological value for erythrocytes is ≤ 5 / µg urine (Kasper 2015). From > 5 erythrocytes per field of view, one speaks of a (micro) hematuria (Manski 2019).

The detection of erythrocytes indicates, for example, nephrolithiasis, urinary bladder inflammation, interstitial nephritis (Keller 2010) or a tumorous event. A false negative result is found with high concentrations of vitamin C or uric acid (Risler 2008).

• 2. e. Conjugated bilirubin, urobilinogen

Normal value: negative or for urobilinogen < 1 mg / dl (Manski 2019).

The detection of urobilinogen > 1 mg / dl and the presence of conjugated bilirubin are indicative ofLeber disease, hemolysis, porphyria and others (Risler 2008).

• 2. f. Glucose:

The normal value is < 1.1 mmol / l in morning urine (Manski 2019).

Positive for glucose is indicated by the Stix only from a value of about 500 mg / l. False negative results are found at a urine pH < 5 (Risler 2008).

Glucosuria can be caused by, for example, diabetes mellitus or proximal tubular kidney damage (Kuhlmann 2015).

• 2. g. Nitrite detection

Normal value: negative (Manski 2019).

Positive nitrite detection occurs due to nitrate reducing bacteria such as E. coli, Klebsia, Proteus mirabilis, Salmonella. False negative results can occur with urine pH around 4 - 5, hyposthenia, polyuria and non- nitrite formers (Risler 2008).

• 2. h. Proteins:

The urine dipstick allows a semi-quantitative assessment for proteins. It detects almost exclusively albumin and this only in the macroalbumin range of > 200 mg / dl. The biuret and trichloroacetic methods show a broader protein spectrum (Herold 2021).

The normal value for albumin is < 30 mg / 24 h, other proteins - especially the Bence-Jones protein - cannot be detected with the Stix.

An increase in albumin is found, for example, in hypertension or diabetic nephropathy (Keller 2010). For detailed information on the determination of the quantity and quality of the proteins, see point 6 below: "Special detection methods".

• 2. i. Ketone bodies:

Ketone bodies are generally not detectable in the urine of healthy individuals (Manski 2019). They originate from fat breakdown and are used by muscle cells as an energy source (Herold 2021). They can be detected, for example, during starvation, in diabetes mellitus as a precursor of ketoacidosis or in alcoholism (Kuhlmann 2015).

• 2. j. Specific gravity:

Normal value 1.003 - 1.030 (Manski 2019).

In the thirst test, the specific gravity increases up to 1,035 g / l and decreases to values up to 1,001 g / l during water stress. Regardless, glucosuria or proteinuria significantly increases the specific gravity, as both have a high specific gravity.

(Herold 2021 /Hegele 2015 / Keller 2010).

• 3. urine sediment

For microscopic examination of the urine sediment, approx. 10 ml of fresh urine is first centrifuged and then approx. 1 drop is applied to the carrier glass. The evaluation always refers to the unit of measurement "per field of view". However, special staining is required for the detection of Decoy cells (Risler 2008).

Indications for microscopic examination are repeated haematuria and / or proteinuria in the strip test (Herold 2021), V. a. involvement of the kidney in a systemic disease or V. a. a kidney disease of as yet unclear genesis (Keller 2010).

In the urinary sediment, statements can be made about:

• 3. a. Erythrocytes:

In microhematuria, microscopically ≥ 2 - 5 erythrocytes / field of view (in the so-called "high power field" [Kasper 2015]) . In clinical practice, the prevalence is between 4 % - 5 % (Herold 2021).

Macrohaematuria, on the other hand, is visible to the naked eye and often occurs together with proteinuria (Manski (2020). In case of macrohaematuria, a prompt clarification should always be made (Herold 2021).

Hematuria is differentiated between glomerular and extra-glomerular hematuria. In the glomerular form, > 5 % acanthocytes are detectable. These represent dysmorphic erythrocytes and are arranged in a typical ring shape with protuberances (also known as "Mickey Mouse ears"). Glomerular hematuria occurs, for example, in glomerulonephritis (Herold 2021).

In extra-glomerular haematuria, iso- or eumorphic erythrocytes are found. These occur, for example, inNephrolithiasis , urinary tract infection or tumors (Kuhlmann 2015).

• 3. b. Leukocytes

Leukocytes occur in high numbers mainly in the context of a urinary tract infection. They are also found in low elevated numbers in proliferative glomerulonephritis.

Eosinophils can occur in interstitial nephritis, chronic pyelonephritis, and others (Kuhlmann 2015).

• 3. c. Tubular cells

These are found particularly in tubular damage to the kidney such as from acute interstitial nephritis, cellular rejection of a graft, acute tubular necrosis (Kuhlmann 2015).

• 3. d. Epithelial cells

Epithelial cells are differentiated into.

• Squamous epithelia:

These originate from the urethra or the external genital area and have no disease value (Keller 2010). Squamous epithelia are found more frequently in women than in men.

• Transitional epithelia:

They line the inner walls of the draining urinary tract from the renal pelvis to the upper part of the urethra and occurin inflammation, nephrolithiasis and tumors.

• Renal epithelia or tubular cells:

These are found in toxic or tubular damage to the kidney and in transplant rejection.

(Rathert 2018)

• 3. e. Cylinder

Urinary cylinders are always outpourings of the tubular lumen and are thus evidential of a renal origin. One differentiates between

• hyaline cylinders:

These can also occur in healthy individuals. In large quantities, however, they are indicative of dehydration or a more severe proteinuria [Kuhlmann 2015]),

• erythrocyte cylinders:

These are typical of glomerulonephritis (Herold 2021).

• Leukocyte cysts:

Found in > 80% in chronic pyelonephritis. They also occur in lupus nephritis (Kuhlmann 2015).

• Epithelial cysts:

These are not specific to any kidney disease. They can occur in cirrhotic kidneys, nephrotic syndrome, after acute anuria, etc (Herold 2021).

• Fat cylinders:

Fat cylinders are typical of marked proteinuria, but can also occur with damage to the tubules of various causes (Kuhlmann 2015).

• 4. urine cytology

For urine cytology, it is recommended to use spontaneous urine, but not 1st morning urine and not 24 h collected urine. Patients, if mobile, should perform light physical movements such as climbing stairs, squatting, etc. beforehand and consume ½ to 1 l of water or tea to increase cell yield(Rathert 2018).

Indications for urine cytology are:

• micro- or macrohematuria
• unexplained dysuria
• unclear alguria
• V. a. or primary diagnosis of a urothelial tumor
• postoperative follow-up of urothelial tumor
• For screening in high-risk patients such as:
  • Analgesic abuse
  • Nicotine abuse
  • occupational exposure to carcinogenic substances
  • in case of radiation therapy in the pelvic area
  • prostate carcinoma
  • gynaecological tumours
• Patients with autosomal dominant HNPCC-Lynch syndrome (Hereditary Non-Polyposis Colorectal Cancer), who have a 50% - 70% risk of developing colorectal carcinoma or 20% - 60% risk of developing endometrial carcinoma (Kaiser 2020).
• if vesico-enteric fistulas are suspected
• annual check-up in patients after kidney transplantation
• in living donors before explantation
• in the case of extraurological tumours with penetrative growth
• V. a. glomerulonephritis to detect dysmorphic erythrocytes
• V. a. a viral infection

(Rathert 2018)

• 5. urine culture / pathogen diagnostics

• 5. a. Flow cytometry:

Flow cytometry, which is an automated and standardized procedure for the classification and quantification of bacteria, represents an initial screening method in this regard. A result is already available after 72 seconds. However, it is not possible to make statements about the type and vitality of the bacteria (Helling 2002).

Flow cytometry can also be used to detect neoplastic urothelia together with conventional cytometry. The sensitivity is then 93 % (Rathert 2007).

• 5. b. Microscopic examination:

By these examinations:

- bacteria, fungi and protozoa can be detected microscopically

- a pathogen cultivation is possible

The pathological limit is 100,000 germs / ml. Immunosuppressed patients or patients with chronic pyelonephritis are an exception. Here the limit is 10,000 germs / ml).

(Kuhlmann 2015)

• 5. c. Bacterial culture:

When creating a bacterial culture, the culture medium is inoculated with 10 µl of urine and then incubated for 24 h in an incubator at 35 degrees. In addition, it is possible to create an antibiogram, which can be read after 48 h (Helling 2002).

Indications for urine culture are:

• in asymptomatic patients:
  • leukocyturia, haematuria or positive detection of nitrite in the case of specific risk factors, e.g. after kidney transplantation or vesicoureteral reflux.
  • after antibiosis in pregnant women, men, complicated urinary tract infection or pyelonephritis
• in symptomatic patients:
  • all patients with the exception of women with a history of a urinary tract infection
  • indications of complicated urinary tract infections in outpatients
  • recurrent urinary tract infections in outpatients
  • persistence of symptoms after completion of antibiotic treatment
  • Indication of a nosocomial urinary tract infection
  • fever or sepsis with as yet unexplained genesis
  • in special clinical situations with a targeted search such as:
  • Immunosuppression
  • before and after interventional procedures of the urogenital tract
  • unexplained pain in the abdomen or flank
  • in the case of a neurogenic bladder emptying disorder (Kuhlmann 2015)
  • in pregnant patients both at first presentation and at 16 weeks gestation
  • After antibiotic therapy in pregnant women, men, complicated urinary tract infection, and pyelonephritis (Manski 2019)

• 5. d. Immunochemical testing

Immunochemical testing procedures involve an antigen (specific) antibody response (Günzler 2013). These tests include, for example, the ELISA (enzyme-linked immunosorbent assay) test.

Immunochemical tests can be used, for example, to detect:

• Pregnancy (Bruhn 2008)
• Drugs (Tauber 2004)
• Microalbuminuria (Gerok 2007)

Microalbuminuria, which is referred to when excretion is between 30 mg - 300 mg / g creatinine (Herold 2021), is of critical importance as it indicates an increased risk of diabetic or hypertensive nephropathy.

Diabetic nephropathy poses the greatest risk for chronic dialysis requirement . Regardless of the cause of microalbuminuria, cardio-vascular mortality is always increased (Dikow 2003 /Kuhlmann 2015).

A false pathological result of microalbuminuria can, for example, be caused by fluorine in women, occur passagerly in fever or, in the case of values < 1 g during the day and protein-free night urine, indicate orthostatic, predominantly harmless proteinuria (Herold 2021).

• 6. special detection methods:

• 6. a. Electrophoretic differentiation of proteinuria.

Proteinuria is defined as a deviation from the physiological protein pattern or an excretion of > 150 mg of protein in 24 h.

Proteinuria is differentiated between:

• microalbuminuria:
  • 30 mg / d - 300 mg / d as an early symptom of diabetic nephropathy.
  • 20 mg / d - 200 mg / d as an early symptom of hypertensive nephropathy
• small molecule proteinuria:
  • up to a maximum of 1.5 g / d due to tubular damage
• large-molecule proteinuria:
  • up to a maximum of 1.5 g / d due to minor glomerulopathies
• small- and large-molecule proteinuria:
  • from 1.5 g / d - 3 g / d by transplant kidney, nephrosclerosis, chronic glomerulonephritis
• large-molecule proteinuria:
  • > 3 g / d due to nephrotic syndrome

(Herold 2021)

• 6. b. Electrophoresis

Electrophoresis can be used to separate proteins based on molecular weight. The following patterns are differentiated:

• Large molecular weight glomerular proteinuria.

These include selective and non-selective proteinuria.

Selective glomerular proteinuria, in which there is increased leakage of albumin (Hofmann 2001), is found, for example, in minimal-change glomerulonephritis, EPH gestosis (serious complication of pregnancy), stage III diabetic nephropathy, and low-activity lupus nephritis (Manski 2019).

Non-selective glomerular proteinuria, in which higher molecular weight proteins such as IgG are detectable in addition to albumin (Hofmann 2001), indicates severe glomerular damage and is caused by, for example, lupus nephritis, glomerulonephritis, EPH- gestosis, and amyloidosis (Manski 2019).

• Small-molecule tubular proteinuria.

Normally, small molecule beta 2 protein is glomerularly filtered and tubularly reabsorbed. However, when there is damage to the tubules, elevated levels of low molecular weight protein are found in the urine (Herold 2021). Damage to the tubules can be caused by, for example, interstitial nephropathy or Fanconi syndrome (Kuhlmann 2015).

• Glomerular-tubular mixed proteinuria

In this case, there is usually a primary glomerular disease with increased glomerular permeability for large-molecule proteins. This causes pronounced secondary changes in the tubules. The glomerular filtration rate is reduced. This combination is often found in glomerulopathies with tubular involvement (Herold 2021) or in diabetics and hypertensives (Bob 2001).

• Prerenal proteinuria

Prerenal proteinuria is also called "overflow proteinuria". In this case, increased low-molecular-weight protein is formed and filtered in the final urine because the tubular reabsorption and catabolism rates have been exceeded. The kidneys themselves are functionally intact (Kuhlmann 2015). These include:

• Bence- Jones- proteinuria

Bence- Jones- proteinuria, which occurs in plasmocytoma, is not detectable by test strip examination. Kuhlmann (2015) therefore recommends that patients with typical symptoms and age should also always have a sulfosalicylic acid sample. If this is negative, further diagnostics are unnecessary.

Bence-Jones proteinuria can be detected by acetate foil electrophoresis and immunoelectrophoresis / immunofixation (Kuhlmann 2015).

• Haemoglobinuria (after haemolytic crisis)
• Myoglobinuria (after muscle trauma).

In the latter two, the urine is discolored red-brown (Herold 2021).

• Postrenal proteinuria

Protein excretion consists of approximately 1/3 physiological high molecular weight proteins such as Tamm- Horsfall protein (excretory product of the kidney) or secretory IgA and IgG from distal sections such as the bladder.

Postrenal proteinuria should be distinguished from these physiological proteins, which occurs in urinary tract infections, e.g., due to local production of immunoglobulins or as exudation due to tumors or bleeding of the urinary tract (Frotscher 2013).

Postrenal proteinuria can be caused by:

• Urinary tract infections
• Nephrolithiasis
• tumors in the area of the uro-genital tract
• artificial protein admixtures
• injuries (plasma proteins)
• menstrual blood (plasma proteins)

(Jocham 2007 / Kuhlmann 2015)

Several possibilities are suitable for differentiating renal from postrenal proteinuria:

• phase contrast microscopy (if > 10 % acanthocytes are detectable, this is an indication of glomerular proteinuria)
• measurement of high and low molecular weight proteins (in postrenal proteinuria, proteins with high molecular weight are found)
• Determination of a2- macroglobulin and IgG (this test can differentiate between renal and postrenal proteinuria from an albumin excretion of > 100 mg / l [Renz 2003]).

(Hofmann 2001)

• 7. four-glass sample

If chronic prostatitis is suspected, the urine should be collected in 4 different containers for subsequent microscopic examination. The following are found in the:

• 1. glass: germs of the urethra
• 2nd glass: germs of the urinary bladder
• 3rd glass: germs of the prostate
• 4th glass (after massage of the prostate): also contains germs of the prostate gland.

As this examination is relatively time-consuming, the 2-glass sample has become established nowadays:

• 1st glass: midstream urine with urinary bladder germs
• 2nd glass (after prostate massage): Here, the first 10 ml of urine are used for the examination, they may contain prostate germs.

(Manski 2019)

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