MAACB Prep Flashcards
Name 3 types of potentiometric electrode
1- redox
2- ion selective membrane ( glass and polymer)
3- PCO2
Define precision , repeatability and reproducibility
Precision is the closeness of agreement of independent results , measured under stipulated conditions
Repeatability is within run precision.
Reproducibility is under changed conditions eg time, operator , calibrators
Name 3 enzymes that can be used to measure glucose
Hexokinase
Glucose dehydrogenase
Glucose oxidase
What is the most widely used glucose method with laboratories
Hexokinase coupled with glucose dehydrogenase , measuring NADH
What is the equation for the glucose Hexokinase method
Glucose + MgATP —HK—->G6P + MgADP
G6P + NAD —G6PD—-> 6-phosophogluconolactone + NADH
NADH measured at 340nm
How many umol of glucose is consumed for every umol NADH?
1
How many calibration points and what calibrator is used for the Hexokinase glucose method
3 point cal
Blank plus MCC1 and MCC 2
What is the LOD, LOQ for serum glucose
LOD= 0.14mmol/L with 95%probability LOQ= 0.28mmol/L with CV 20%
What is the LOD and LOQ for urine/csf glucose
LOD= 0.056mmol/L 95%propbability LOQ= 0.056mmol/L 20%CV
What is the linearity of glucose HK Abbott method
0.28 - 44.40mmol/L
What kind of interference does haemolysis cause Glucose HK spectro method ?
Haem concentrations >5g/L causes negative interference
What kind of interference does ict and lip cause glucose HK method ?
Positive interference >55mmol/L
Fasting glucose reference range ?
Adult- 2.8-5.6 mol/L
Describe the glucose oxidase reaction ?
Glucose + O2 —GO—-> gluconlactone + H2O2
H2O2 + chromogenic oxygen acceptor (e.g o-diasidine ) —peroxidase—> chromogen colour + H2O
What is mutarotase used for?
In kits to convert alpha D-glucose to beta D-glucose for use in glucose oxidase polarography reaction - measuring oxygen consumption
Where is albumin synthesised ?
Parenchymal cells of the liver
+ fall in oncotic pressure
- IL6
What is the function of albumin
Non-specific transport protein eg FFA, ca2+,Zn2+, unconjugated bilirubin and many drugs.
Contributes to oncotic pressure
Minor buffer of H+ ions
Possible causes of low albumin by decreased synthesis?
Inadequate nitrogen intake
Malabsorption
Chronic liver disease
Possible cause of low albumin by increased catabolism?
Sepsis
Possible cause of low albumin by redistribution?
Ascites
Oedema
Sepsis
Possible cause of low albumin by increased loss?
Protein-losing enteropathy
Nephrotic syndrome
Loss of plasma eg.burns
How do you convert mg/dl to mol/L?
Mol/L= (mg/dL X 10) / Mw
List 4 hormones increased by stress
Glucocorticoids eg cortisol
Catecholamines eg epinephrine
Growth hormone
Prolactin
List causes of elevated urate
Gout Renal failure Leukaemia Multiple myeloma Toxiemia of pregnancy
List causes of raises bilirubin
Increased hepatocellular damage
Infra and extra hepatic biliary tree obstruction
Haemolytic disease
Neonatal physiological jaundice
List causes of in vitro haemolysis
Incorrect needle size
Incorrect tube size selection (difficult bleed)
Prolonged tourniquet
Vigorous mixing of tubes
List biochemical analytes that change with dehydration
Urea Creatinine Sodium HB Protein ADH
What is the ref method for lactate ?
There isn’t one
What is the reaction for the lactate oxidase method?
L-lactate + O2 —-LOD—-> Pyruvate + H2O2
H2O2 + 4-AA+ H+ ——Peroxidase—> chromogen + 2H2O
548nm
Fluoride oxalate sample
What is precision?
Closeness of agreement between independent results obtained under stipulated conditions.
What is repeatability ?
Closeness of agreement between results of successive measurements under the same conditions (within run precision )
What is reproducibility?
Closeness of agreement between results of measurements performed under changes conditions ( time , operators , calibrators )
What is drift?
Instrument or reagent instability over time
What is accuracy?
Closeness of the agreement between the result of a measurement and the true concentration of an analyte.
What is the limit of blank?
Highest apparent concentration in analyte-free material. 20 rots of sample with no analyte (0 calibrator)
LOB= mean(blank) + 1.645(SD blank)
What is LOD?
Lowest concentration confidently separated from blank 20 rots if verifying /60 if establishing)
LOD = LOB + 1.64( SD low conc sample)
What is LOQ?
Aka functional sensitivity-limit of reporting . Lowest concentration with acceptable reproducibility CV <20%
What is analytical sensitivity?
The smallest quantities that the assay measures
LOB, LOD, LOQ
Define positive likelihood ratio, how is it calculated and how does it influence clinical decision making?
LR+ is the probability that a person with the disease test positive (TP) divided by the probability that a person without the disease test positive (FP)
LR+= sensitivity/1-specificity
LR- = 1-sensitivity/specificity
Applying likelihood ratios can change the probability of a diagnosis eg low enough to rule out disease or high enough to start treatment
Name 4 methods for urinary free cortisol
LC-MS/MS
Beckman coulter -EIA(comp chemilum) 30mins
Roche - ECLIA ( comp electro chemilum IA) 18mins NB:biotin
Abbott -CMIA( comp chemilum Microparticles IA) 30 mins