Day 3 Self Urinalysis
TP, Blood, Nitrate & pH
Urine pH
• Lungs and kidneys are major regulators of acidbase content
• First morning specimen slightly acidic at 5.0 to
6.0
• Postprandial specimen more alkaline
• Normal range is 4.5 to 8.0
• No absolute values are assigned
Urine pH (cont’d)
• Considerations include
– Acid-base content of the blood
– Patient’s renal function
– Presence of a urinary tract infection
– Patient’s dietary intake
– Age of the specimen
• A pH above 8.5 is associated with an
aged/improperly preserved specimen, so a fresh
specimen should be obtained
Summary of Clinical Significance of
Urine pH
• Respiratory or metabolic acidosis/ketosis
• Respiratory or metabolic alkalosis
• Defects in renal tubular secretion and reabsorption
of acids and bases—renal tubular acidosis
• Renal calculi formation
• Treatment of urinary tract infections
• Precipitation/identification of crystals
• Determination of unsatisfactory specimens
pH-Reagent Strip Reactions
• Needed to measure between 5.0 and 9.0 in one half or one unit
increments
• Double-indicator system reaction
– Methyl red = 4 to 6 red/orange to yellow
– Bromthymol blue = 6 to 9 green to blue
Methyl red + H+ → Bromthymol blue − H+
(Red/Orange → Yellow)
(Green → Blue)
• Interference
– No known substances interfere with urinary pH measurements performed
by reagent strips
– RUNOVER from Protein
Protein
• Most indicative of renal disease
– Proteinuria seen in early renal disease
• Normal = <10 mg/dL or 100 mg/24 h
• Low-molecular-weight serum proteins are filtered;
many are reabsorbed
• Albumin is primary protein of concern
• Other proteins include
– Vaginal, prostatic, and seminal proteins
– Tamm-Horsfall (uromodulin)
Clinical Significance
• Presence requires determination of normal or
pathological condition
• Clinical proteinuria = 30 mg/dL, 300 mg/24 h
• Variety of causes
– Prerenal
– Renal
– Postrenal
Prerenal Proteinuria
• Conditions affecting the plasma, not the kidney
• Transient, increase levels of low-molecularweight plasma proteins, acute phase reactants,
exceed reabsorptive capacity
• Rarely seen on reagent strip (not albumin)
Bence Jones Protein (BJP)
• Multiple myeloma (plasma cell myeloma)
• Immunoglobulin light chains
• Multiple myeloma confirmation is serum
electrophoresis
Renal Proteinuria
• Glomerular or tubular damage
– Glomerular proteinuria
– Microalbuminuria
– Orthostatic (postural) proteinuria
– Tubular proteinuria
Glomerular Proteinuria
• Damage to glomerular membrane
• Impaired selective filtration causes increased
protein filtration leading to cellular excretion
• Abnormal substances deposit on the membrane
– Primarily immune disorders result in immune
complex formation
• Lupus erythematosus, streptococcal glomerulonephritis
– Amyloids and other toxins
Blood
• Hematuria: intact RBCs
– Cloudy red urine
• Hemoglobinuria: product of RBC destruction
– Clear red urine
• Any amount of blood greater than five cells per
microliter of urine is considered clinically significant
• Chemical tests for hemoglobin provide the most
accurate means for determining the presence of blood
• The microscopic examination can be used to
differentiate between hematuria and hemoglobinuria
Blood (cont’d)
• Hematuria: intact RBCs, cloudy red urine
• Damage to renal system
– Renal calculi
– Glomerular disease
– Tumors
– Trauma
– Pyelonephritis
– Exposure to toxic chemicals
– Anticoagulants
Blood (cont’d)
• Hemoglobinuria: clear, red urine
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Transfusion reactions
Hemolytic anemias
Severe burns
Infections/malaria
Strenuous exercise/RBC trauma
Brown recluse spider bites
• Hemoglobinuria may result from the lysis of red
blood in dilute, alkaline urine
• Hemosiderin: yellow brown granules in sediment
Blood (cont’d)
• Myoglobinuria: heme-containing protein in muscle
tissue; clear, red/brown urine
– Rhabdomyolysis: muscle destruction
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Muscular trauma/crush syndromes
Prolonged coma
Convulsions
Muscle-wasting diseases
Alcoholism
Drug abuse
Extensive exertion
Cholesterol-lowering statin medications
Blood
Reagent Strip Reactions
• Principle pseudoperoxidase activity of
hemoglobin
• Catalyze a reaction between the heme
component
– Hemoglobin and myoglobin
– Chromogen tetramethylbenzidine
– Produce an oxidized chromogen
• Green-blue color
Blood
Reagent Strip Reactions
hemoglobin
H2O2 + chromogen --------------- oxidized chromogen + H2O
peroxidase
• Two charts corresponding to different reactions
• Free hemoglobin shows uniform color
• Intact RBCs show a speckled pattern on pad
– Report: trace, small (1+), moderate (2+), large (3+)
– Sensitivity 5 RBCs/μL
Blood
Reaction Interference
• False-positive
– Menstrual contamination, strong oxidizing agents,
bacterial peroxidases
• False-negative
– Ascorbic acid >25 mg/dL
– High SG/crenated cells
– Formalin
– Captopril
– High concentrations of nitrite
– Unmixed specimens
Nitrite
• Clinical significance
• Rapid screening test for the presence of urinary tract
infection (UTI)
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Cystitis (initial bladder infection)
Pyelonephritis (tubules)
Evaluation of antibiotic therapy
Monitoring of patients at high risk for urinary tract
infection
– Screening of urine culture specimens (in combination
with LE test)
Nitrite
Reagent Strip Reaction
• Tests ability of bacteria to reduce nitrate (normal
constituent) to nitrite (abnormal)
• Greiss reaction: nitrite reacts with aromatic amine to
form a diazonium salt that then reacts with
tetrahydrobenzoquinoline to form a pink azodye
• Correspond with a quantitative bacterial culture
criterion of 100,000 organisms/mL
• Results: negative and positive
Nitrite
Reagent Strip Reaction (cont’d)
Acid
para-arsanilic acid or sulfanilamide + NO2 —————→ diazonium salt
(nitrite)
Acid
diazonium salt + tetrahydrobenzoquinolin —————→ pink azodye
Nitrite
Reaction Interference
• False-negative
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Nonreductase-containing bacteria
Insufficient contact time between bacteria and urinary nitrate
Lack of urinary nitrate
Large quantities of bacteria converting nitrite to nitrogen
Presence of antibiotics
High concentrations of ascorbic acid
High specific gravity
Negative results in the presence of even vaguely suspicious
clinical symptoms should always be repeated or followed by a
urine culture
Nitrite
Reaction Interference (cont’d)
• False-positive
– Old specimens (bacterial multiplication)
– Highly pigmented urine
– Pink edge or spotting on reagent strip is considered
negative
– Check automated readers manually for color
interference