B - Chapter VI: Carbohydrates Flashcards
use (?)
serum, plasma or whole blood
whole blood values (?) lower than serum or plasma
10 - 15%
erum or plasma should be refrigerated and separated from the cells (?) to prevent substantial loss thru glycolysis
within1 hour
separated unhemolyzed serum at rm temperature is stable for
8 hr; ref temperature for 48 - 72 hr
preferred additive :
sodium fluoride (gray top)
: approximately 8 - 10 hr fast (not >16 hr)
FBS
: immediate processing to prevent bacterial utilization of glucose
CSF glucose
: only for monitoring of diabetics and not for diagnosis
urine sugar
Chemical methods − done in an
alkaline medium
− glucose + boiling water —-> (?) (enol anion form) : reduce metallic ions
eneidol
Alkaline Copper reduction Tests
Folin-Wu
Nelson-Somogyi
Neocuproine
total reducing substances (true reducing substances and saccharoids) measured
Folin-Wu
barium sulfate enables measurement of true reducing substances only
Nelson-Somogyi
Campbell and King method
Neocuproine
neocuproine (7,9- dimethyl-1,10-phenanthroline) —> cuprous-neocuproine complex (yellow-orange)
Neocuproine
arsenomolybdic acid —> arsenomolybdenum blue
Nelson-Somogyi
phosphomolybdic acid —> phosphomolybdenum blue
Nelson-Somogyi
Alkaline Ferric reduction tests
- Johnson method
- Folin/ Prussian blue method
- Hagedorn-Jensen method
− reverse colorimetric method
− more specific than copper reduction
Alkaline Ferric reduction
− ferricyanide —> ferrocyanide
Alkaline Ferric reduction
Condensation methods
(a) with aromatic amines
(b) with phenols
Ortho-toluidine method by Dubowski (reference method)
Condensation methods with aromatic amines
based on the ability of carbohydrates to form Schiff bases with aromatic amines
Condensation methods with aromatic amines
glucose + ortho-toluidine —-> N-glycosylamine: Schiff base (green) 630 nm
Condensation methods with aromatic amines
Condensation methods with aromatic amines interfering substances:
galactose, mannose and aldopentose
glucose —> water + hydroxymethylfurfural (HMF)
Condensation methods with phenols
HMF + anthrone —> green colored compound
Condensation methods with phenols
Enzymatic methods
(a) Glucose Oxidase method
(b) Hexokinase method
(c) Glucose Dehydrogenase (GDH)
most specific enzyme reacting with only β-D-glucose
Glucose Oxidase method
glucose + O2 + H2O — GOD —> gluconic acid + H2O2
Glucose Oxidase method
H2O2 + reduced chromogen — POD—> oxidized chromogen + H2O
Glucose Oxidase method
mutarotase : added to convert alpha to beta glucose
Glucose Oxidase method
Methods to quantify H2O2 :
- Gochman and Schmitz
- Trinder
3-methyl-2-benzathiazolinone hydrazone + N,N-dimethylaniline —> indamine dye (590-66- nm)
Gochman and Schmitz
p-aminophenazone + phenol —-> purple product (quinoneimine)
Trinder
2,2-azine-di(3-ethyl bezothiazoline-(6)-sulfonic acid —> colored chromogen
Miskieweis
- measures the amount of oxygen consumed in the glucose oxidase method
POLAROGRAPHIC OXYGEN ELECTRODE
POLAROGRAPHIC OXYGEN ELECTRODE
To prevent the formation of oxygen from H2O2 (by catalase present in some GOD preparations), it is removed by inclusion of two additional reactions:
❖ H2O2 + ethanol —– catalase—— Acetaldehyde + H2O
❖ H2O2 + H+ + 2I- — molybdate —- I2 + 2H2O
- recommended for type 1 diabetics
Self-Monitoring of Blood Glucose: point of care device
- to maintain levels as close to normal as possible
Self-Monitoring of Blood Glucose: point of care device
- whole blood glucose testing using capillary blood as sample
Self-Monitoring of Blood Glucose: point of care device
- more accurate, less interferences than glucose oxidase methods (REFERENCE method)
Hexokinase method
- not affected by uric acid and ascorbic acid
Hexokinase method
- false decrease: hemolyzed sample and elevated bilirubin levels
Hexokinase method
- can also be used for urine, CSF and serous fluids
Hexokinase method
− glucose + ATP —hexokinase —> glu-6-phosphate + ADP
Hexokinase method
− glu-6-phosphate + NADP —G-6-PD —> NADPH + H + 6-phosphogluconate (340 nm)
Hexokinase method
Glucose + NAD —— GDH —– Gluconolactone + NADH + H+
Glucose Dehydrogenase (GDH)
Coenzyme I: NAD
Coenzyme II: NADP
Glucose Dehydrogenase (GDH)
− increased plasma glucose levels
HYPERGLYCEMIA
− caused by imbalance of hormones
HYPERGLYCEMIA
− normally : insulin is secreted : enhance entry of glucose into the liver, muscle and adipose and alters glucose metabolic pathways
HYPERGLYCEMIA
Laboratory Findings in Hyperglycemia
- increased glucose in plasma and urine
- increased urine specific gravity
- increased serum and urine osmolality
- ketonemia and ketonuria
- decreased blood and urine pH (acidosis)
- electrolyte imbalance
CLASSIFICATION of DIABETES MELLITUS:
- Type 1 DM
- Type 2 DM
- Gestational diabetes mellitus (GDM)
- Due to other causes:
- monogenic diabetes syndromes
- diseases of the exocrine pancreas
- drug- or chemical-induced diabetes
due to autoimmune β-cell destruction, usually leading to absolute insulin deficiency
Type 1 DM
due to a progressive loss of β-cell insulin secretion frequently on the background of insulin resistance
Type 2 DM
diabetes diagnosed in the 2nd or 3rd trimester of pregnancy that was not clearly overt diabetes prior to gestation
Gestational diabetes mellitus (GDM)