Investigation of Non-Protein Nitrogen Compounds Flashcards
What is the main source of ammonia in the body?
Protein catabolism (deamination of amino acids).
How is ammonia eliminated?
Converted into urea in the liver and excreted by the kidneys.
What enzyme is responsible for the first step of the urea cycle?
Carbamoyl Phosphate Synthetase I (CPS I).
What is the most common sample type for ammonia measurement?
Plasma (collected in EDTA or lithium heparinate tubes).
What precautions should be taken when collecting ammonia samples?
Transport on ice, process immediately to avoid false elevation.
What are the main methods for measuring ammonia?
Colorimetric (Berthelot reaction), Enzymatic, and Electrochemical methods.
What is the normal range of ammonia in blood?
14 – 38 µmol/L.
What is the normal range of ammonia in urine?
30 – 60 mmol/24h.
What are the causes of hyperammonemia?
Liver failure (cirrhosis, hepatitis), Urea cycle disorders, Organic acidemias, Metabolic acidosis.
What clinical symptoms suggest hyperammonemia?
Confusion, tremors, encephalopathy, vomiting, seizures, coma.
A neonate has hyperammonemia, vomiting, and lethargy. What is the likely diagnosis?
Urea cycle disorder (OCT or CPS deficiency).
Why should patients avoid smoking before ammonia testing?
Smoking increases plasma ammonia levels.
What test can confirm a urea cycle disorder?
Measurement of urea cycle enzyme activity and blood amino acid chromatography.
Why is ammonia measured in hepatic encephalopathy?
High ammonia levels correlate with neurological deterioration.
How is hyperammonemia treated?
Lactulose, low-protein diet, sodium benzoate, arginine supplementation.
What is the main function of urea?
Excretion of nitrogenous waste via urine.
Where is urea synthesized?
Liver (urea cycle).
How is urea eliminated?
Filtered by the kidneys, partially reabsorbed, and excreted in urine.
What is the most common sample type for urea measurement?
Serum or heparinized plasma.
What are the main methods for measuring urea?
Enzymatic (urease-based), Colorimetric (Berthelot reaction), and Electrochemical techniques.
What is the normal range of urea in blood?
0.15 – 0.45 g/L.
What is the normal range of urea in urine?
18 – 30 g/day.
What conditions cause hypoazotemia (low urea)?
Liver failure, malnutrition, pregnancy.
What conditions cause hyperazotemia (high urea)?
Kidney disease, dehydration, high protein intake, infections.
A patient has high urea but normal creatinine. What does this indicate?
Dehydration.
What is the most common clinical use of urea measurement?
Assessing kidney function.
A diabetic patient has high urea and creatinine. What is the likely diagnosis?
Diabetic nephropathy.
Why is urea not a perfect marker of kidney function?
It is influenced by diet, hydration, and catabolic states.
What test is better than urea for kidney function assessment?
Serum creatinine and eGFR (estimated glomerular filtration rate).
How does liver failure affect urea levels?
Decreases urea production (hypoazotemia).
What is creatinine?
A waste product of muscle metabolism (from creatine breakdown).
How is creatinine excreted?
Filtered by the kidneys and excreted in urine.
What is the most common sample type for creatinine measurement?
Serum or heparinized plasma.
What is the gold standard method for creatinine measurement?
IDMS (Isotope Dilution Mass Spectrometry).
What is the normal range of creatinine in blood?
Men: 6–12 mg/L, Women: 5–10 mg/L, Children: 4–9 mg/L.
What is the normal range of creatinine in urine?
1–2 g/day.
What are the causes of hypercreatininemia?
Acute & chronic renal failure, dehydration, muscle disease.
A 60-year-old diabetic has high creatinine, high urea, and proteinuria. What is the likely diagnosis?
Chronic kidney disease (CKD).
How is eGFR calculated?
Using formulas like MDRD, CKD-EPI, or Cockcroft-Gault.
What is the difference between creatine and creatinine?
Creatine stores energy in muscles; creatinine is its waste product.
What are the three main types of jaundice?
Pre-hepatic, Hepatic, Post-hepatic.
What is the normal range of total bilirubin in adults?
6 – 10 mg/L.
What condition causes isolated unconjugated hyperbilirubinemia?
Gilbert’s syndrome.
What enzyme deficiency causes Crigler-Najjar syndrome?
Glucuronosyltransferase deficiency.
What type of jaundice is seen in biliary obstruction?
Post-hepatic (cholestatic) jaundice.
What is the main cause of pre-hepatic jaundice?
Excessive hemolysis (e.g., hemolytic anemia, sickle cell disease).
What is the enzyme responsible for bilirubin conjugation in the liver?
UDP-glucuronosyltransferase (UGT).
How does intrahepatic cholestasis affect bilirubin levels?
Both conjugated and unconjugated bilirubin increase.
A patient has pale stools and dark urine. What type of jaundice is most likely?
Post-hepatic (obstructive) jaundice due to bile duct obstruction.
Why should bilirubin samples be protected from light?
Light degrades bilirubin, leading to falsely low results.
What type of jaundice occurs in newborns due to immature liver enzymes?
Physiological jaundice.
What condition causes conjugated hyperbilirubinemia with black liver pigmentation?
Dubin-Johnson syndrome.
What is the most common method for measuring bilirubin?
Diazo reaction (Van den Bergh method).
A patient with liver failure, ascites, and jaundice has high conjugated bilirubin. What is the diagnosis?
Hepatic jaundice due to liver cirrhosis.
What genetic disorder leads to isolated unconjugated hyperbilirubinemia with no hemolysis?
Gilbert’s syndrome.
