Chem exam 3

What is heme

Porphyrin ring with ferrous iron chelated at center

What is a Porphyrin

Chemical intermediates in heme synthesis

Porphyrins (stability, color, fluorescence)

Stable, red-violet to red-brown, fluoresce red when excited by light near 400 nm

Porphyrinogens (stability, color, fluorescence)

Highly unstable, colorless, do not fluoresce

Reduced form of porphyrins

Protoporphyrin

PROTO is primarily excreted in feces

Uroporphyrin

URO is excreted primarily in urine

Corproporphyrin

COPRO is excreted in either urine or feces depending on pH

What is the rate controlling enzyme of heme synthesis

ALA synthase

As heme increases, ALA synthase production decreases (negative feedback)

Erythropoietic porphyria

Build up of heme precursors in BM

Hepatic porphyria

Build up of heme precursors in the liver

Cutaneous porphyrias are caused by an excess of

Porphyrin production and excretion

Acute porphyrias are caused by an excess of

Early precursors (ALA, porphobilinogen)

Symptoms of cutaneous porphyrias

Chronic skin condition. Biosensitivity, blisters, lesions

Acute porphyria symptoms

Abdominal pain/vomiting, tachycardia, psychiatric symptoms

Treatment for cutaneous porphyrias

Avoid sun exposure (porphyrins react when exposed to light), blood transfusions, BM transplant

Acquired porphyria

Impaired heme synthesis caused by something other than a biochemical defect. ex cirrhosis, obstructive jaundice

Symptoms similar to acute porphyria

What does a positive PBG mean

Acute porphyria

What does positive porphyrin and negative PBG mean

Cutaneous porphyria

Heme degredation pathway

Heme, biliverdin, unconjugated bilirubin (bound to albumin), conjugated bilirubin, urobilinogen, urobilin

Watson Schwartz test

PBG reacts with Erlichs reagent to form red/pink color

Hoesch test

Erlichs reagent in strong acid reacts with PBG to form cherry-red color. Faster and more specific

What are the two PBG screening methods

Watson-Schwartz and Hoesch

PBG

Porphobilinogen, a precursor to porphyrin

What method is used for quantitation of PBG and ALA

HPLC with fluorescence

Is the majority of bilirubin conjugated or unconjugated

Unconjugated

When heme is broken down, globin is

Reused by the body

Unconjugated bilirubin travels to the liver bound to

Albumin

What enzyme conjugates bilirubin in the liver

UDP-glucuronyl transferase

What is conjugated bilirubin conjugated with

Glucuronic acid

Intestinal bacteria convert bilirubin into

Urobilinogen

Unconjugated bilirubin

Indirect, insoluble

Conjugated bilirubin

Direct, soluble

What form of bilirubin is toxic to brain and nervous tissue

Unconjugated bilirubin that is not bound to albumin

How is bilirubin eliminated

As urobilin, with the red/brown pigment

Adult total bilirubin RR

0.2-1 mg/dL

Adult conjugated bilirubin RR

0-0.2 mg/dL

Adult unconjugated bilirubin RR

0.2-0.8 mg/dL

Is total bilirubin lower or higher in infants

Higher

When is jaundice noticable

3-5 mg/dL

Bilirubin specimen requirements

Fasting serum/plasma, no hemolysis/lipemia, protect from light

Kernicterus

Accumulation of unconjugated bilirubin in brain of infants. Treatment is UV light therapy

Why run a control near 20 mg/dL for neonatal bilirubin?

Critical concentration for exchange transfusion. Can only do in infants <1 month

Neonatal hyperbilirubinemia cause

Due to increased hemolysis at birth and deficiency of UDP-glucuronyl transferase

Prehepatic jaundice cause

Excessive amount of bilirubin is presented to liver. ex hemolytic anemia

Prehepatic jaundice lab findings

Unconjugated hyperbilirubinemia, no bilirubin in urine

Hepatic jaundice cause

Impaired cellular uptake, defective conjugation, or abnormal secretion of bilirubin by liver (AKA poorly functioning liver)

Unconjugated hyperbilirubinemia examples

Gilbert syndrome (common), Crigler-Naijar syndrome (rare, deadly)

Conjugated hyperbilirubinemia examples

Dublin johnson syndrome, Rotor’s syndrome (both benign)

Post hepatic jaundice cause

Impaired excretion of bilirubin caused by mechanical obstruction of the flow of bile. ex gallstones/tumor

Posthepatic jaundice lab findings

Increased serum conjugated and unconjugated bilirubin, conjugated bilirubin in urine (not normal), decreased urine urobilinogen

Clay colored stool

Unconjugated hyperbilirubinemia definition

>80% of total bilirubin is onconjugated. Seen with hepatic or prehepatic issues

Conjugated hyperbilirubinemia definition

>50% of total bilirubin is conjugated. Unable to excrete conjugated bilirubin (post-hepatic)

Jendrassik Grof

Bilirubin reacts with diazo reagent. Caffeine benzoate as accelerator to make all forms of bilirubin soluble. Used to measure total and conjugated bilirubin

What was the first clinically useful serum bilirubin method

Malloy Evelyn with 50% methanol as the accelerator

Direct spectrophotometric bilirubin for neonates (<1 month)

Absorbance at 455- absorbance at 575 (for correction of hemolysis in babys serum)

Why can you only do the direct spectrophotometric method of direct bilirubin on infants less than 1 month

Their serum does not contain lipochromes that would interfere with the assay

Urobilinogen analytical method

Urobilinogen reacts with Erlichs reagent to form red color, measured spectrophotometrically

Reflectance spectrophotometry for bilirubin

Thin film (dry slide), uses Jendrassik Grof diazo method

When would you see enzymes in the serum

Following cellular injury or from degraded cells

Activator

Inorganic cofactors (ex Chloride ions)

Coenzyme

Organic cofactor (ex NAD)

What is the enzyme rate of reaction dependent on

pH, temp, enzyme/substrate concentration, cofactors, inhibitors

Zero order kinetics

When reaction rate depends on concentration of enzyme (substrate and cofactors in excess)

What phase of an enzyme reaction do we want to measure

Linear

IU

The amount of enzyme that will catalyze the reaction of 1 micromol of substrate to product per minute

AST

Aspertate aminotransferase, AKA SGOT

Used for liver assessment but not most specific enzyme

When are the highest levels of AST seen

Cirrhosis and viral hepatitis

What is the coenzyme for AST and ALT

Pyridoxal phosphate

AST measurement

Malate dehydrogenase coupled reaction

ALT

Alanine aminotransferase, SGPT

More specific to liver than AST (ALT—> liver and lactate dehydrogenase)

ALT measurement

Lactate dehydrogenase coupled reaction

ALP

Alkaline phosphatase, highest concentrations found in liver and bone

What is the activator for ALP, ACP, and CK

Magnesium

What is ALP used for

Evaluation of obstructive hepatobiliary and bone disorders

Pagets disease (what enzyme is increased/decreased)

High levels of ALP

What enzyme is not found in cardiac or skeletal muscle

GGT

ALP assay

Bowers-McComb method at pH 10.2

What ALP isoenzyme is heat sensitive

Bone

What are the 4 major ALP isoenzymes

Liver, bone, placenta, intestinal

GGT

Gamma glutamyl transferase. Can help distinguish liver damage from muscle damage (not found in cardiac/skeletal muscle)

What enzyme is used to monitor liver disease in teens

GGT

What enzyme is used to monitor alcohol consumption

GGT

ACP

Acid phosphatase. Found in many places, including seminal fluid

What enzyme was historically used for diagnosis of prostate cancer

ACP, replaced by PSA

ACP assay

p-Nitrophenyl phosphate at pH 5

What does tartrate inhibition affect

Decreases prostatic ACP

CK

Creatine kinase. Highest levels in skeletal muscle, heart muscle, and brain tissue

What enzyme is not found in liver or RBCs

CK

CK diagnostic significance

Rhabdomyolysis, damage to cardiac/skeletal muscle

CK assay

Oliver Rosalki (reverse reaction)

CK MM

Skeletal and cardiac muscle, found in healthy people

CK MB

Mostly cardiac muscle, significant indicator of AMI

CK BB

Brain tissue

What is anti-M immunoinhibition used to measure

CK-MB and LD-1

CK specimen

Increased by hemolysis, inactivated by sunlight

LD

Lactate dehydrogenase. Highest concentration found in heart, liver, skeletal tissue, and erythrocytes

What enzyme is increased with pernicious anemia and hemolytic disorders

LD

LD coenzyme

NAD

LD sample

No hemolysis, no freezing/refrigerating, separate immediately

LD-1/2

(HHHH) Heart tissue, RBCs, renal cortex. LD-2 is same (HHHM)