Flashcards in Diabetes testing Deck (40):
Levels of plasma glucose?
- normal: FPG: less than 100 mg/dL
- increased risk for diabetes "pre-diabetes":
impaired fasting glucose (IFG) - 100-125
impaired glucose tolerance (IGT) - 2 hr OGTT 140-199
A1C greater or equal to 6.5%
FPG greater or equal to 126
2 hr OGTT is greater or equal to 200
- sx hyperglycemia RPG greater or equal to 200
*** dx must be confirmed on a subsequent daby by measuring any one of the criteria
What is the sensitivity and specificity of 126 level if usuing the 2 hr OGTT greater or equal to 200 as a reference standard?
- specificity: greater than 95% (ability to rule in)
sensitvity about 50% (ability to rule it out)
- a person that has a FPG of 126 or higher highly likely to have diabetes but a person with level of 120 may still have diabetes when using 2 h OGTT criteria as reference
What factors affect blood sugar?
- emotional stress
- physical stress
When are hormones relesased to increase blood sugar?
- in times of stress
- part of fight or flight response
- physical or emotional stress: surgery, infection, stroke, MI, emotional stress and anxiety
What can elevated blood sugar other then diabetes, IFG, or IGT?
meds: ****steroids, beta-blockers, nicotinic acid, and estrogents
- **stress hyperglycemia: usually seen in acutely ill pt
- others: cushing's syndrome, acromegaly, pheochromocytoma, glucagonoma, liver disease, and pancreatitis
What are the ADA recommendations for screening?
- FPG screening every 3 years beginning at age 45 years
- consider screening at an earlier age ( or more frequently if older than 45) if diabetes risk factors are present
- w/o risk factors: can start to screen all persons age 45 and older
- BMI greater or equal to 25 + 1 or more risk factors
- screening tests: A1C, fasting plasma glucose, 2 hr OGTT
- if normal (A1C less than 5.7, FPG less or equal to 100) retest in 3 years
Risk factors of DM?
- age: greater or equal to 45
- BMI: greater or equal to 25
- FmHx of DM in 1st degree relative
- Hx of gestational DM
- high risk ethnicity (African american, hispanic, native american, asian american, pacific islanders)
- HDL less or equal to 35
- TGs greater or equal to 250
- A1C greater or equal to 5.7
- vascular disease
- sedentaray lifestyle
What should be done for dx of diabetes?
- plasma samples
- point of care testing for A1C not recommended for dx
- finger stick blood glucose isn't used for dx
- if significantly elevated finger stick glucose - draq a serum sample to confirm
Difference b/t fingerstick vs plasma glucose?
- venous glucose levels may be higher than capillary levels : for fasting samples and random testing
- venous levels lower than capillary: 2 hr after oral glucose load
What is the A1C measuring?
- plasma glucose only gives us snapshot in time. In reality there are many fluctuations with blood sugar throughout the day
- the hemoglobin A1C is way to measure the mean glucose level over 3 months.
- hemoglobin that is formed in new RBCs enters circulation without any glucose attached
- RBCs are freely permeable to glucsoe
- glucose becomes irreversibly attached to heomoglobin at a rate dependent upon prevailing blood glucose
- correlates best with mean blood glucose over the previous 8 to 12 weeks
How was mean glucose levels measured before the A1C?
- est. with frequent blood glucose levels during the day:
before and 90 minutres after:
breakfast, lunch, dinnerand at bedtime
(7 sticks per day)
- greater or equal to 6.5% diabetes
- 5.7-6.4% abnormal
- less than 5.7% is normal
Sources of error in A1C?
- A1C values are influenced by A1C survival
- whe RBC turnover is low (delayed) such as with iron, vitamin B12, or folate deficiency anemia, there are a disproportionate number of older RBCs which can lead to falsely high values
- In rapid cell turnover leads to greater proportion of younger RBCs and falsely low A1C values. Examples include pts with hemolysis and those tx for iron, Vit B12, or folate deficiency
Whta are factors that could increase an A1C?
- iron deficiency anemia
- alcohol toxicity
- lead toxicity
- late pregnancy due to iron deficiency anemia
- genetic variants: Hgb S, Hgb C traits
What are factors that could decrease A1C?
- hemolytic anemia
- chronic blood loss
- chronic renal failure
How often should a routine hemoglobine A1C be done?
- at least 2x yearly if meeting DM tx goals (usually around 7)
- test q 3 months if previous medication change or not meeting tx goals
What is a fructosamine test and when is it useful?
- many proteins other than hemoglobin also undergo glycosylation
- 1-2 weeks of avg blood glucose control
- serum sample needed
- not very widely used
What should be considered when doing a fructosamine test?
- if albumin level is abnormal than fructosamine values must be adjusted, falsely low levels with rapid albumin turnover
- increased vit C or hyperthyroidism can interfere with fructosamine levels
- may be useful if you want to know more recent blood sugars, don't have to wait 3 months and also more accurate in pregnant, anemic, blood loss, abnorm RBCs: sickle cells (not measuring RBCs - hemoglobin)
What do you measure in the urine?
Urine glucose significance
- glucose in blood is normally filtered at glomerulus with almost complete reabsorption taking place in proximal tubule
- glucose in urine signifies that filtered load is exceeding the absorptive capability of proximal tubule- it will continue on to collecting duct and show on the urine dipstick
- blood level at which glucose appears in urine varies from individual to individual, but usually occurs at levels greater than 180 mg/dL
WHat is glucosuria?
noted when blood glucose exceeds 180
- leads to osmotic diuresis
- overall this isn't normal, and needs a follow up blood sugar
Ketones in urine?
- produced in liver
- part of fatty acid metabolism
- increase when not enough insulin to use glucose for energy
- more common in type 1 because there isn't any insulin so breaking down fatty acids into ketones (DKA)
What are the 3 types of ketones?
- beta-hydroxybutrate (in DKA most are in this form)
- acetic acid
- there are normally small amts of ketones present in serum and urine (which are not detected by conventional testing)
- positive test for ketones indicates considerable excess in the blood
Urine ketones and DKA?
- in a pt with DKA, urine may be negative for ketones if severe renal insufficiency exists (kidneys may be unable to filter ketones)
- test reacts strongle to acetoacetic acid but not with beta-hydroxybutyrate. In DKA most of ketones present are in the form of beta-hydroxybutyrate (negative or weakly positive urine ketone shouldn't sway clinician from possibility of ketoacidosis if presentation is suggestive
- where else might you see ketonuria in absence of DKA?
- in low carb diets, starvation or vomiting
When should you test
-elevated blood sugars greater than 300
-when suspicious for DKA
When will ketones be detectable in the urine?
- poorly controlled DM
- strict Atkins diet
- certain types of anesthesia
- some metabolic disorders
When will ketonuria be false positive?
- meds: levodopa, phenazopyrine, and valproic acid
- Vit C
What is albuminuria?
- show up on regular urine dipstick as + for protein needs to be greater or equal to 300 mg (proteinuria)
- moderately increased albuminuria (microabluminuria)
albumin excretion 30-300 mg/g
Screening for albuminuria?
- 5 years after dx of type 1
- upon dx of type 2
- then annually for all diabetics
What is an albumin to creatinine ratio (ACR)?
- spot urine albumin/creatinine ratio:
preferably first morning void, correlates well with 24 hr urine sample, microalbuminuria = 30-300 mg albumin/g of creatinine
- 24 h urine collection is the std
Dx of diabetic nephropathy?
- confirm a positive result with additional tests over next 3-6 months
- 2 out of 3 samples that are abnormal within 6 month period = diabetic nephropathy
Why should SMBG be done?
- to maintain good glucose control
- allow adjustments of insulin and diet content to be made based on immediate feedback of glucose results
- allows timely intervention for low glucose readings to avert serious hypoglycemic events
When should SMBG be done?
- frequency of testing depends on many factors
- fasting AM
- before and after meals
- before, during and after exercise
- before bedtime
- periodically 2-3 AM (Somogyi?)
How often should SMBG be done in type 1 and type 2 DM?
- type 1 DM: at least 3x daily
- type 2 DM: depends on degree of control and what meds the person is taking
- should be done fasting AM, before and after meals, before, during and after exercise, and before bedtime
Helpful ways to get good drop of blood from fingertip?
- rinse fingers with warm water
- shaking hand below the waist
- squeezing or milking fingertip
Sources of error in SMBG?
- operator error: failure to calibrate the meter correctly, dirty meters, inadequate hand washing, improper storage of test strips
- with decreasing blood sugars there is less accuracy
- use of multiple sites (fingertips and forearms)
levels of blood glucose in forearm and fingerstick?
- initially in first 120 minutes: fingerstick will have higher glucose levels
- 120-210 minutes glucose levels higher from forearm stick
What is continuous glucose monitoring?
- real-time monitoring
- can be coupled with insulin pump
- measures interstitial fluid by: needle sensor inserted subq or whole device implanted subq
- not as accurate as fingerstick