Interpretation of the Urinalysis (Part 2) - The Dipstick

Summary

This video script is the second part of a three-part series on urine dipstick analysis. It explains how to check a dipstick and the significance of abnormal findings, covering tests for specific gravity, pH, glucose, protein, ketones, and more. It also discusses the clinical utility of these tests in diagnosing various conditions.

Takeaways

• 📚 The script is part of a three-part series focusing on the interpretation of urine dipstick tests, aiming to explain how they are checked and the significance of abnormal findings.
• 🔍 A urine dipstick is a reagent strip with pads that test for various potential contents in urine, providing a quick, semi-quantitative assessment.
• 💧 The dipstick works by dipping it into urine or using a pipet to soak the strip, then comparing the color changes against provided standards after a specific waiting time.
• 🌡️ Specific gravity measures the relative density of urine compared to water, typically ranging from 1.001 to 1.035, and can indicate hydration status or kidney function.
• 🔄 The order of pads on the dipstick is arranged in increasing reaction duration, with glucose requiring the shortest time to read and leukocyte esterase the longest.
• 🍋 Urine pH can range from 4.5 to 8.0 and can help diagnose conditions like renal tubular acidosis or monitor for certain drug effects, but its interpretation should be contextualized with other lab results.
• 🚰 Glucose in urine (glycosuria) is rare and can indicate hyperglycemia, proximal tubal dysfunction, or genetic defects in renal glucose transport.
• 🩸 Hematuria (blood in urine) detected by dipstick is sensitive for hemoglobin and myoglobin, and can indicate bleeding in the urinary tract or muscle breakdown.
• 🌀 Proteinuria detected by dipstick is most sensitive for albumin and can indicate various kidney diseases, but is less sensitive for non-albumin proteins.
• 🌐 Leukocyte esterase and nitrites are used to aid in diagnosing urinary tract infections (UTIs), with leukocyte esterase indicating inflammation and nitrites indicating bacterial presence.
• 📉 Ketones, bilirubin, and urobilinogen tests on the dipstick have limited clinical utility and are not routinely reported in some labs due to their variable sensitivity and specificity.

Q & A

What is a urine dipstick test?

A urine dipstick test involves using a reagent strip with a series of pads that provide a quick, semi-quantitative assessment of various potential contents of urine. The specific contents tested may vary slightly between different manufacturers.

How does a urine dipstick work?

The reagent strip is either dipped directly into urine or a disposable pipet is used to soak the strip. After wiping off the excess fluid, the strip is compared against provided standards after a predetermined time, which is usually about 30 seconds but may vary depending on the manufacturer.

What is the significance of specific gravity in urine?

Specific gravity is a measure of relative density, specifically the ratio of the density of urine to the density of water. It can vary from 1.001 to about 1.035 depending on hydration status and can be used to assess conditions like primary polydipsia or diabetes insipidus.

What conditions can affect the specific gravity of urine?

Conditions that can alter specific gravity include excessive hydration (diabetes insipidus), dehydration or SIADH (syndrome of inappropriate secretion of anti-diuretic hormone), impaired perfusion (CHF, cirrhosis), glycosuria, proteinuria, and recent administration of IV contrast.

What is the normal pH range of urine?

The normal pH range of urine can vary from 4.5 to 8.0, depending on the physiological state of the kidneys. The pH can be used to diagnose conditions like renal tubular acidosis or to monitor urine alkalization.

Why is urine pH not a reliable indicator of a patient's acid-base status?

Urine pH is highly dependent on diet and should not be used to infer anything about a patient's acid-base status without an ABG (arterial blood gas) and metabolic panel. For example, a urine pH of 5 does not necessarily mean that a patient's serum pH is abnormal.

What is glycosuria and what causes it?

Glycosuria is the presence of glucose in the urine. It can be caused by serum hyperglycemia, where too much glucose is filtered and overwhelms the tubular reabsorption capacity, or by proximal tubal dysfunction such as Fanconi syndrome.

What is the significance of heme in urine?

Heme in urine is detected by the urine dipstick and is highly sensitive for hemoglobin. It can indicate bleeding in the urinary tract or conditions like rhabdomyolysis (acute muscle breakdown). However, contamination with substances like semen can cause false positives.

Why are leukocyte esterase and nitrites important in diagnosing UTI?

Leukocyte esterase is an enzyme released by white blood cells and is used as a qualitative measure of white blood cells in the urinary tract. Nitrites detect the presence of bacteria that convert normally present nitrates in urine into nitrites. While leukocyte esterase is a marker of inflammation, nitrites are more specific for actual bacteria, making them useful in diagnosing UTIs.

Why are ketones detected in urine less reliable in diagnosing ketoacidosis?

The test used by dipsticks to detect ketone bodies only detects acetoacetate and acetone, while the predominant ketone body formed in ketoacidosis is beta-hydroxybutyrate. This makes the dipstick test less sensitive for clinically relevant ketoacidosis.

What is the significance of bilirubin and urobilinogen in urine?

Bilirubin and urobilinogen in urine can indicate conditions like hemolysis or biliary obstruction. Hemolysis can increase the excretion of urobilinogen, while biliary obstruction can lead to increased bilirubin in urine due to the liver's inability to excrete it.