Clinical Chemistry Pt. 1 - Prof. Jedidiah Calunsag April 2024

Urine Analysis

• Urine analysis checks for the volume of acid and alkaline present, not the exact pH.
• Measurement of acid and alkaline involves adding a base reagent and a blue indicator to the urine sample.
• The binding of OH- with H+ causes the color to change from blue to colorless (neutral), indicating the presence of acid.

pH Measurement

• pH measurement involves measuring the concentration of H+ (hydrogen ions) in the urine, regardless of whether the urine is acidic or alkaline.

Osmolality Measurement

• Osmolality measures the changes in colligative properties of a solution.
• Colligative properties include boiling point, freezing point, vapor pressure, and osmotic pressure.
• As osmolality increases, freezing point and vapor pressure decrease.
• The formula for osmolality is: (2(sodium) + glucose/20 + BUN)/3 = milliosmole/kg.

Amperometry

• Amperometry measures the current or voltage generated by the activity of a specific ion.
• It involves the reaction of two chemicals, producing electricity.
• Example: Serum sample with silver silver chloride in an ion-selective electrode (ISE) measures oxygen diffusion inside the ISE membrane.

Clinical Features

• Pompe disease: protuberant abdomen due to hepatomegaly and renomegaly, rickets, and failure to thrive.
• Muscle phosphorylase deficiency: exercise intolerance, muscle cramps, dark red urine after intense exercise.
• Niemann-Pick disease: accumulation of sphingomyelin, macrophage cannot metabolize sphingomyelin due to lack of sphingomyelinase, resulting in foamy cytoplasm.

Lipids

• Phospholipids are the most abundant lipids in cell membranes.
• Lecithin and sphingomyelin are used to determine fetal lung maturity.
• L/S ratio: lecithin divided by sphingomyelin, must be ≥2.

Cholesterol

• Cholesterol is used to produce steroid hormones and is a component of cell membranes.
• Sources of cholesterol: 90% endogenous (from the body).

Clinical Chemistry

• Conversion factors: albumin, bilirubin, BUN, sodium, potassium, chloride, creatinine, glucose, thyroxine, triglyceride, uric acid.
• To remember: same with total protein, b171rubin, Cr8inine, and cholesterol.

Analytical Methods

• Spectrophotometry: measures the light transmitted by a solution.
• Beer's Law: unknown substance is directly proportional to absorbed light and inversely proportional to transmitted light.
• Blanking technique: used to correct absorbance caused by reagent's color and hemoglobin.
• Disadvantage: turbidity by lipid is not corrected, remedy: ultracentrifugation dissolves lipids.

Flame Emission Photometry

• Measures light emitted by a single atom burned in a flame.
• For unexcited elements, absorption spectroscopy is used.

Atomic Absorption Spectroscopy

• Measures light absorbed by atoms dissociated by heat.
• Uses a spectro flame to dissociate molecules.

Fluorometry

• Measures light intensity emitted by a molecule after excitation by electromagnetic radiation.
• Uses 2 monochromators.
• Disadvantage: quenching effect.

Molarity

• Molarity: number of moles of solute per liter of solution.
• Formula: Mole = g / mw.
• Example: 2 mole HCl in 500 mL, answer: 4M.
• Example: 300g H2SO4 in 500 mL, explanation: convert 300g H2SO4 into moles using the formula.