Biochemical Testing of Urines Flashcards
How should you store reagent strips?
- Avoid exposure to moisture, chemicals, heat, and light
- Store at room temp below 30°C, but don’t freeze or refrigerate
- Keep dessicant packet inside bottle, and close vial immediately after use
When should QC be performed on the reagent strips?
- Use both pos and neg controls a minimum of once every 24 hours
- When a new bottle of strips is opened
- When a new lot is received
What is the normal specific gravity?
1.003-1.030
Urine w/ a specific gravity of 1.010
Isosthenuria
Urine w/ a specific gravity of < 1.010
Hyposthenuric
What is the most common cause of hyposthenuria?
Diabetes insipidus or renal disease
Urine w/ a specific gravity > 1.010
Hypersthenuric
Limitation of specific gravity
Only determines specific gravity from 1.000-1.030 on 0.005 increments
What lowers the specificity gravity
Highly buffered alkaline urine lowers readings
How do you correct for alkaline urine?
When pH is ≥ 7 add 0.005 to the strip reading if it is being read manually
What is specific gravity NOT affected by?
- Radiographic dyes
- Increased glucose, urea, or protein
Principle of pH
Double indicator of methyl red and bromthymol blue
Reference range for pH
There isn’t a reference range for urine pH b/c broad variances occur daily in normal patients; will measure from 5.0-9.0 w/ 1.0 or 0.5 increments
When is acidic urine common during the day?
Morning (5.0-6.0)
- Urine below 5.0 is suspicious of tampering
When is alkaline urine suspicious of improper storage or tampering?
pH > 8.0
Meats and high protein diet lead to what pH in the urine?
Acidic urine
Vegetarian diet leads to what type of pH in the urine?
Alkaline urine
What is it called when you have basic urine after a large meal?
Alkaline tide
Condition where HCO3- is not reabsorbed and H+ are not excreted; leads to ACIDIC blood and ALKALINE urine?
Renal tubular acidosis
What cells contain leukocyte esterase?
- Granulocytes (neutrophils, eosinophils, basophils, and monocytes)
- Not found in RBCs, lymphocytes, and epis
Principle of leukocyte esterase test
Indoxylcarbonic acid ester → leukocyte esterase → indoxyl + diazonium salt → purple azodye
Leukocyte esterase is associated w/ what infections?
- Bacterial
- Trichomonas
In bacterial infections w/ a positive leukocyte esterase, what result usually accompanies it?
Positive nitrite rxn
Positive leukocyte esterase may be found w/o bacteriuria in what 4 conditions?
- Trichomonas
- Chlamydia
- Yeast infections
- Inflammation of renal tissues
What is the specificity of leukocyte esterase?
Specific for esterase
What causes false positive for leukocyte esterase?
- Vaginal contamination
- Medications that falsely color urine
What causes false negatives for leukocyte esterase?
- ↑ glucose > 3 g/dL
- ↑ protein > 500 mg/dL
- High specific gravity
- Certain medications
Principle of nitrite test
Greiss rxn
Clinical significance of nitrites
Bacteria convert nitrates into nitrites. Nitrites are an ABNORMAL finding
Nitrites indicates the presence of what?
GN bacteria
Bacterial infection that backflows from the bladder to the ureters and kidneys?
Pyelonephritis
What causes false positives for nitrite?
- Falsely colored urine
- Improper storage allowing for bacterial proliferation?
What causes false negatives for nitrite?
- Ascorbic acid (vitamin C)
- The enzyme is only found in GN bacteria (Enterobacteriaceae is the leading cause of UTIs)
Principle of proteins test
Protein error of indicators
What protein is primarily tested?
Albumin
Proteinuria is an indicator of ____ ____ and is often the very first indicator
Renal disease
Reference range of protein
Varies 1-14 mg/dL (150 mg/dL) is ok, but > 30 mg/dL is considered clinical proteinuria
Seven general reasons for protein in the urine
- Glomerular damage
- ↑ glomerular pressure (exercise
- ↓ tubular reabsorption
- Fanconi’s syndrome (PCT)
- Orthostatic/postural proteinuria
- Overflow proteinuria
- Benign causes
Protein
- Causes of glomerular damage → proteinuria
- Amyloidosis
- Toxic substances
- SLE (immune complexes)
- Streptococcal glomerulonephritis (immune complexes)
Protein
- Causes of increased glomerular pressure → proteinuria
- Exercise
- Dehydration
- Hypertension
Cause of decreased tubular reabsorption → proteinuria
- Toxic substances
- Viral infections
- Fanconi’s syndrome (damages to proximal tubules)
Describe rthostatic/postural proteinuria and best urine specimens to collect
- Standing puts pressure on renal vein which leads to protein in the urine but laying down relieves the pressure.
- Best to collect day and night time urine specimens
Conditions that lead to PRE-RENAL overflow proteinuria
- Septicemia (acute phase reactants)
- Hemolytic episode (hemoglobinuria)
- Muscle injury (myoglobinuria)
- Immunoglobulins (Bence-Jones proteins)
Conditions that lead to POST-RENAL overflow proteinuria
- Inflammations due to bacterial or fungal infections
- Presence of blood
- Prostatic fluid or sperm
Benign causes of proteinuria
- Exposure to the cold
- Exercise
- Dehydration
- Fever
Protein sensitivity on Chem strip
6 mg/dL albumin
What causes false negatives for protein?
Strips detect albumin, proteins other than that may not be detected
What causes false positives for protein?
- Very alkaline urines ( > 9 mg/dL)
- High specific gravity
Albumin present in the urine below the detectable limits of a routine urine strip
Microalbuminuria
Principle for detecting microalbumenuria
Uses sensitive dye-binding rxn that is specific for albumin
A test that is used to confirm the presence of protein (esp. in alkaline urine)
Sulfosalicyclic acid (SSA)
Principle of SSA
Cold precipitation test
Describe the cold precipitation test
- Protein will precipitate in the solution when SSA is added to produce a cloudy specimen
- It will precipitate all proteins (not just albumin)
What will excess protein present look like when shaken?
Foamy when shaken
What is the most common test performed on urine and why?
Glucose! B/c of its importance in detection and monitoring of patients
Principle of testing glucose
Double sequential enzyme rxn
Renal threshold for glucose
180 mg/dL
Hyperglycemic patients will present w/ glycosuria. What patients are these?
- Diabetes and gestational diabetes
- Conditions: pancreatitis, Cushing’s syndrome, hyperthyroidism (opposes fxn of insulin leading to hyperglycemia)
What causes patients w/ normal glucose levels to still present w/ glycosuria?
- Damage to tubules that hinders reabsorption
- Occurs in end stage real disease
- Osteomalacia
- Fanconi’s syndrome
- ↓ reabsorption threshold in pregnancy
What causes false positives for glucose?
Oxidizing agents
What causes false negatives for glucose?
- Ascorbic acid
- High ketones
- High specific gravity
- Drugs
What test should e performed for patients < 2 years old to detect reducing sugars other than glucose?
Clinitest
What is a pathological condition that can lead to severe mental retardation, liver dysfunction, and cataracts?
Galactosemia
Limitation of the clinitest
- Not as specific or sensitive as glucose strips
- Man interfering reducing substances (ascorbic acid, drugs)
What is in the highest concentration in a patient who is oxidizing fatty acids?
Beta-hydroxybutyrate
Principle of the ketones test
Acetoacetate + sodium nitroprusside → purple color
Ketonemia and ketonuria occurs when the body metabolizes _____ _____ due to inadequate amounts of _______
Fatty acids; CHOs
Three general reasons for ketonemia
- Inability to use carbohydrates (type 1/gestational diabetes)
- Inadequate intake of carbs (starvation/diets)
- Loss of CHOs (vomiting/starvation/dieting=Atkins diet)
Ketone testing specificity is primarily sensitive to ____
Acetoacetate
What causes false positives for ketones?
Drugs that contain sulfhydryl groups
What causes false negatives for ketones?
- Improper storage and handling
- Improper storage of strips
- Uncapped specimens
- Acidosis
Principle of urobilinogen test (2 methods)
- Multistix (Ehrlich’s rxn)
- Chemstrip (Diazo rxn)
Urobilinogen
- What is the increased production of bilirubin leading to increased urobilinogen produced and consequently increased urobilinogen in urine
Prehepatic mechanism
Urobilinogen
- What conditions lead to prehepatic urobilinogen?
- Hemolytic anemia
- Sickle cell
- Hereditary spherocytosis
- Thalassemia
- Pernicious anemia
- Txn rxns
Urobilinogen
- What is it when a damaged liver is not capable of reabsorping urobilinogen from the portal circulation leading to additional urobilinogen entering the blood stream?
Hepatic mechanism
Urobilinogen
- Conditions that may cause hepatic urobilinogen?
- Hepatitis
- Cirrhosis
Urobilinogen
- What is it called when conjugated bilirubin will not be able to enter the intestine due to blockage in the bile duct leading to no urobilinogen production?
Post-hepatic mechanism
What causes false positives for urobilinogen?
- p-aminosalicylic acid
- Sufamethoxazol
What causes false negatives for urobilinogen?
- Exposure to light
- High nitrites
Principle of bilirubin test
Diazo rxn
What test has greater sensitivity to bilirubin?
Ictotest
In what mechanism is bilirubin negative?
- Provide examples
Prehepatic mechanism
- Hemolytic disease-like txn rxns
- Hemolytic anemia
In what mechanism does conjugated bilirubin “leak” from damaged hepatocyte back into the blood, thus increasing bilirubin?
- Provide examples
Hepatic mechanism
- Hepatitis
- Cirrhosis
In what mechanism is conj bilirubin unable to pass though the bile duct and thus back up not the liver and bloodstream leading to bilirubin in the urine?
- Provide examples
Post-hepatic mechanism
- Bile duct blockage
Bilirubin and urobilinogen
- Which one (or both) is positive in prehepatic (hemolytic disesase)?
- Bilirubin: negative
- Urobilinogen: positive
Bilirubin and urobilinogen
- Which one (or both) is positive in hepatic (liver damage)?
- Bilirubin: positive
- Urobilinogen: positive
Bilirubin and urobilinogen
- Which one (or both) is positive in posthepatic (bile duct obstruction)?
- Bilirubin: positive
- Urobilinogen: negative
What causes false positives in bilirubin?
- pH > 9.0
- Some medications
What causes false negatives in bilirubin?
- Ascorbic acid
- High nitrites
- Improper storage
Blood
- What all does it detect?
- Hemoglobin
- Intact RBCs
- Myoglobin
Principle of the blood test
Based off of the peroxidase-like activity of hemoglobin
Blood
- What is hematuria?
- Clarity?
- Hematuria → intact red cells in the urine
- Clarity → cloudy (RBCs seen microscopically)
Blood
- What causes hematuria?
- Trauma
- Renal calculi
- Advanced glomerular damage
- Infection
- Neoplasms
Blood
- What is hemoglobinuria?
- Clarity?
- Color?
- What should you look for?
- Hemoglobinuria → hgb in the urine
- Clarity → usually clear
- Color → yellow to red to brown
- Should look for hemosiderin granules
Blood
- Hemoglobinuria is caused by what?
Associated w/ hemolysis
- Hemolytic disease
- Poisoning
- Burns
- Txn rxn
- Paroxysmal nocturnal hemoglobinuria (PNH)
Blood
- What is myoglobinuria?
- Clarity?
- Color?
- Myglobinuria → myoglobin in the urine
- Clarity → clear
- Color → reddish brown
Blood
- Myoglobinuria is caused by what?
Associated w/ muscle destruction
- Traumatic accidents
- Alcoholism or drug use
- Muscle wasting disease
What causes false positives when testing for blood?
- Menstrual contamination
- Microbial peroxidases
What causes false negatives when testing for blood?
- Ascorbic acid
- Unmixed specimens
- High specific gravity leading to crenated RBCs
What situation makes it impossible to interpret a reaction?
In highly color urine from medications or pigments from certain foods
What is the purpose of the ictotest?
Confirmatory test for bilirubin
