Urine Reagent Strip Testing and Clinical Significance

Vocabulary practice flashcards generated from urinalysis testing parameter charts.

Specific Gravity Reference Range (Urine)

Random $1.003 - 1.035$

Specific Gravity Chemical Reaction

$$\text{Polyelectrolytes} + \text{ions in urine} \rightarrow H^+ \text{liberated and cause colour change}$$

Specific Gravity Dipstick Limitation

The dipstick method only detects ionic solutes, which can lead to false negatives for non-ionic solutes.

pH Test Reference Range & Indicators

Reference range is $5 - 8$. Indicator reaction uses methyl red & bromothymol blue, changing from orange to yellow, green to blue.

Leukocytes Dipstick Reaction

$$\text{Ester} + \text{granulocytic esterases} \rightarrow \text{aromatic compound} + \text{diazonium salt} \rightarrow \text{purple colour}$$

Leukocytes False Negatives

Large amounts of glucose or high SG cause WBCs to crenate and prevent esterase release.

Leukocytes False Positives

Genital discharge, bleach or $H_2O_2$, and drugs that turn red in acid.

Greiss Reaction (Nitrite Test)

$$NO_2^- + \text{aromatic amine} \rightarrow \text{diazonium} + \text{quinoline} \rightarrow \text{pink}$$

Nitrite Test Clinical Significance

Bacteria that commonly cause UTIs reduce dietary nitrate to nitrite.

Nitrite False Negatives

Occurs when bacteria do not reduce nitrate, there is insufficient incubation time, or there is an absence of dietary nitrate.

Protein Error of Indicators

Buffered indicator ($pH = 3$) releases $H^+$ ions in the presence of protein, causing a colour change (yellow to green-blue). The test is very sensitive to albumin.

Protein Dipstick False Negatives

Globulins, Bence-Jones, & mucoproteins are less reactive.

Protein Dipstick False Positives

High alkaline urine (acidify urine & repeat protein), dipsticks held in urine too long, and drugs that turn red in acid.

Glucose Renal Threshold

$$8.9 - 10.0\,mmol/L$$

Glucose Dipstick Reaction

$$\text{Glucose} + O_2 \rightarrow \text{GOD} \rightarrow \text{gluconic acid} + H_2O_2 \rightarrow \text{POD} \rightarrow H_2O + O_2 + \text{chromogen} \rightarrow \text{oxidized chromogen (colour change)}$$

Glucose Dipstick False Negatives

Ascorbic acid (Vitamin C).

Ketones Dipstick Reaction

$\text{Acetoacetic acid} + \text{sodium nitroprusside} \rightarrow \text{buffer} \rightarrow \text{purple}$ (less sensitive to acetone).

Ketones Specimen Requirement

Sample must be fresh because acetoacetic acid is lost in urine at room temperature due to decarboxylation & bacterial destruction.

Urobilinogen Reaction (Siemens vs. Roche)

Siemens: Ehrlich's aldehyde + urobilinogen = salmon colour. Roche: Diazonium salt + urobilinogen = red azo dye (salmon).

Urobilinogen False Negatives

Old samples where urobilinogen is oxidized to urobilin (yellow).

Bilirubin Urine Excretion Principle

Only conjugated bilirubin can be excreted in the urine (associated with hepatic jaundice and post-hepatic jaundice).

Bilirubin Diazotization Reaction

Roche: Diazo reagent + conjugated bilirubin $\rightarrow$ azobilirubin (rose-beige). Siemens: Diazo reagent + conjugated bilirubin $\rightarrow$ azobilirubin (brown, purple).

Siemens Bilirubin Confirmation

With the Siemens method, positive results must be confirmed with Ictotest.

RBCs / Hemoglobin Dipstick Reaction

Based on the peroxidase activity of hemoglobin: $H_2O_2 + \text{Hemoglobin} \rightarrow H_2O + O_2 + \text{chromogen} \rightarrow \text{oxidized chromogen (green)}$.

RBCs / Hemoglobin False Positives

Oxidants (bleach, $H_2O_2$) and Myoglobin.

Hematuria Clinical Causes

Kidney trauma, bleeding, strenuous exercise, prolonged exposure to cold, menstruation.

Hemoglobinuria Clinical Causes

Incompatible blood transfusion, lysis due to infection, hemolytic anemia, prolonged pounding.