Clinical Biochem Flashcards
Types of lab tests
Blood tests: plasma and or serum, RBC, WBC
Urine tests
Others eg. Stool, ample fluid (saliva and sweat)
Static- current level in blood, urine ornother tissues- for nutrients often reflects most recent intake
Functional: measures the functional consequences of a nutrient deficiency- limit the nutrient dependant biological function (reflects long term intake). Abnormal metabolite due to dysfunction of an enzyme as a result of a nutrient deficiency
Whole body HB for age deficiency, erythrocyte glutathione peroxidase activity for Se. Alternatively tests may measure physiological or behavioural functions eg. Dark adaption for vit A, taste acuity for axon, muscle function (hand grip strength) for protein energy.
Dietitians involvement in tests
Cannot directly order, must provide recommendation for referral by doctor. Not all tests are rebatable. This is for the purpose of nutrition assessment, nutritional monitoring and screening for or ruling out other conditions
Reference ranges for normal and abnormal results
Plus or minus two standard deviations around the mean value of the healthy population. Each lab may have slight variation.
Reflect what is common rather than what is healthy, since world is become more unhealthy this may be problematic. May be age or gender specific.
Interpreting result outside of the reference range
Not always clear cut.
Not all outside reference range indicate physiological abnormality. However the fourther away from the mid point of the reference range, the higher the probability that it indicated a physiological abnormality- esp for vitamins and minerals. Eg it has clinical significance. For some tests there is clinical sig for a high result but low for a low result and vice versa. Need to use judgement and critical thinking.
Reasons for looking at lab yests
Direct link with nutrition assessment, goal setting and/ or monitoring.
Interpreting other info in the nutritional assessment. Inflammatory markers help wth interpreting albumin, iron studies. Understand the patients general clinical conditions. suitability for nutrition intervention or shape goals of nutrition management. Eg. Risk of refeeding syndrome
Blood or urine tests
Can provide earliest indication of some nutrient deficiencies and excesses. Confirm nutritional diagnosis made on basis of clinical signs and symptoms. Assess affect of nutritional therapy.
Limitations-
Blood used because easily obtained but may not be the best indicator
Concentrations in blood subject to homeostatic control do may vary little
Tend to reflect recent intake or supplement
May not be body compartment that reflects storage/ function
Hair/ nails analysis may be useful for some trace elements
Vitamins
Vit A: plasma retinol/ carotene.
Vit B1 thiamin: whole blood (preferred), or plasma B1
erythrocyte transketolase activity, urinary B1
Vit B2 riboflavin: whole blood B2, urinary B2, % activation of erthrocyte glutathione reductase.
Vit B3 niacin: urinary N1- methyl-nicotinamide
Vit B6 pyridoxine- RBC pyridoxal and pyridoxine.
Folate: RBC folate
B12: serum B12, hologranscobalamine (active B12), urinary methlmalonic acid
Biotin: serum
Homocysteine: serum
Vit c- plasma of urine
Vit D- serum 25-Oh Vit D
Vit E- serum tocopherol
Vit K- prothrombin time
Antioxidants: serum of plasma total: antioxidant status
Minerals
Ca: 24 hours urinary Ca excretion, plasma ionised Ca, serum PTH, Vit D, bone mineral debsiometry
Cr: serum and Rhine
Iodine: urine iodine/ creatinine ratio
Fe: serum Fe, TIBC, ferritin, transferring saturation
Zn: plasma, RBC, 24 hour urinary excretions nd serum albumin (Zn binding protein which may affect values)
Mg: serum? RBC? WBC? 24 hour urinary excretion
Se: serum or whole blood or RBC
Lipid rations
LDL: HDL ideal <3.0
Chol: HDL normal <4.5 ideal <4. May predict individuals risk of developing atherosclerosis with ratios >8 associated with greatly increased risk of MI
Trig: HDL normal <1.8 ideal <1
High ratio associated with small HDL particle size, metabolic syndrome, insulin resistance, >risk of MI, coronary atherosclerosis, >risk CVD/ all cause mortality
Density of LDL and HDL
Small dense HDLs formed when TRIGs high (easily excreted via kidneys dropping HDL levels) > risk CVD. Small dense LDLs more atherogenic and formed with > visceral fat, low fat/ high carb diets, insulin resistance/ diabetes/ high trigs. Can easily slip bw endothelial cells and gain access to the inside of the wall of the artery where they cause damage leading to atherosclerotic plaque. Large LDL particles are harmless because they are too big to get past endothelium and into walls of artery. Apoliprotein B (structural component of lipoproteins), if raised suggests that there are many small dense LDLs- better than just taking LDL. Normal <1.2g/L, ideal <0.9g/L
Glycaemic control: blood glucose
Varies throughout day
Normal BGL (random): 3.0-7.7mmol/L. A random post prandial BGL >11.1mmol/L is diabetes
Fasting BGL:
Normal: 3-6mmol/L (ideal <5.4)
Impaired glucose tolerance: 6-<7mmol (at risk)
Diabetes: >7mmol/L
Confirm with GTT
Fasting BGL affected by
Stress/ acute trauma High GI foods, large or low CHO volume Insulin resistance Excess endogenous of exogenous insulin Medications that increase BGL such as steroids, antidepressants, statins Medications that decrease BGL include aspirin, menoamine oxidase inhibited Exercise before test Pregnancy Severe liver disease
Oral glucose tolerance test
Fast overnight, then 75g oral glucose load/ test blood glucose at 2 hours
Fasting BGL >7mmol= diabetes
5.1-6.9mmol= gestational diabetes
1 hour BGL GMD >10mmol
2 hours BGL T2DM >11mmol or GDM >8.5-11hours
Insulin levels can also be measured which can help diagnose insulin resistance (hyperinsulinaemia)
Fasting insulin 4-10 mU/L ideal
Helpful info in patients who can’t lose weight or to confirm risk of developing T2DM despite normal BGL
Calculating insulin resistance
Homeostatic model assessment (algorithm)
HOMA1- fasting glucose x fasting insulin / 22.5. Ideal <2.8 (diabetes >5)
Mainly used in research
Increasingly in general practice
Glycaemic control treatment targets
Not realistic goal to normalise blood glucose in diabetics.
Good diabetes control often takes as BGL of
<6mmol/L before breakfast
4-8 before meals (T1DM)
6-8 before meals (T2DM)
<10 post prandially
Blood glucose targets are individualised because there may be different concerns amongst people eg history of hypoglycaemia
