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33 Cards in this Set
- Front
- Back
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Explain the rationale for performing serum osmolality assays.
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Osmolality assays tell us the osmotic pressure which is exerted by all of the solutes in a solution
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Expected ranges for serum and urine osmolality assays
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Serum- 289-308 mOsm/kg
Urine: 300-900 mOsm/kg, -A healthy persons urine osmolality should be up to 3 times greater than their serum - Reference range of serum to urine osmolality is 1.0 to 3.0 - A ratio of 1.0 says the nephrons aren't doing anything to the urine |
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Describe how alterations in blood osmotic pressure can cause dehydration, edema, and hypertension.
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-If blood osmolality increases fluid will be drawn into the blood from the interstitial fluid causing hypertension and dehydration.
-If blood osmolality is decreased water will be drawn into the interstitial compartment causing hypotension and edema |
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Osmolal Gap explanation and equation
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Osmolal gap is the difference between measured osmolality with an osmometer vs. the calculated osmolality
Osmol gap= (mmol Na+)(1.86) + (Glucose mg/dl)/(18) + (BUN mg/dl)/(2.8) -normal gap is 0-20 mmol/L |
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Explain the principles of freezing-point depression osmometers
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Uses serum or urine and super cools the sample to -7 c. The sample is vibrated rapidly to release the heat of fusion that has been trapped during the rapid cooling. As this is released the sample reaches its freezing point and the temp is measured.
- the degree of freezing-point depression below that of pure water is directly proportional to the total number of particles in the solution - This is the preferred type for drug toxicology screening |
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Explain the principles of vapor pressure depression osmometers
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-Most common method for plasma and urine osmolality.
- The presence of solute in an aqueous solution reduces the evaporation of the water and exhibits an inverse relationship of concentration and vapor pressure. - These types under-quantitate highly volatile compounds like alcohols |
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Explain the principles of colloid osmotic pressure osmometers
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Proteins have a significant effect on osmotic pressue in vivo, but in vitro they aren't measured "worth a darn" in a VP or FP depression osmometer
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Explain the fate of dietary fructose and galactose, and explain why the only sugar found in fasting patients blood should be glucose
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-Fructose and galactose are converted into glucose by the liver's isomerase enzymes.
- After about an hour post-prandial all of the sugars in the blood will have been converted to glucose |
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Explain why patients with hereditary galactosemia or hereditary fructosemia would have galactose or fructose in their fasting blood or urine
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These patient's livers lack the isomerase enzymes necessary to convert fructose or galactose into glucose
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What is the normal fasting blood glucose range? How is this level maintained by insulin and glucagon
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-Normal fasting- 70-119 mg/dL
- Insulin is the ONLY hormone that lowers blood sugar by allowing glucose to be transported into adipose and muscle cells - Glucagon is the PRIMARY hormone which replenishes glucose levels - all other hormones serve to ELEVATE glucose levels |
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Von Gierkes Disease
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Patients liver totally lacks Glucose-6-phosphate-phosphatase.
-These patients are chronically hypoglycemic because glycogen cannot replenish glucose levels. -Liver cannot get rid of glycogen so it starts to store toxic amounts. -Diagnostic test is Epinephrine Tolerance Test |
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Explain why severe hepatitis, hypothyroid disease, and addison's disease may cause abnormally low blood glucose levels
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Hepatitis- liver cannot store adequate amounts of glycogen to meet the body's need for glucose reserves
Hypothyroid- insufficient production of T3 and T4 results in inadequate lipolysis and glycogenolysis Addison's- lack of cortisol production hinders glycogenolysis and gluconeogenesis |
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Major clinical features of Type 1 diabetes -IDDM
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-pronounced glycosuria
- Very little to no insulin (insulin shock - Severe metabolic acidosis - extremely high blood levels of ketone bodies |
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Major clinical features of Type 2- NIDDM
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Type 2 is the MILD version
-Normal insulin levels - Glycosuria is mild - MILD ketones |
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Explain 2 hour post-challenge blood glucose
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Patient is given a standardized load of pure glucose
- FBS is included in test to give baseline - ADA/WHO recommended replacement test for the 5HGTT for people who do not have a FBS over 126mg/dL -A value over 200 is diagnostic for DM |
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Recommended glucose loads for children, adults, and pregnant women
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Children- 1.75 grams/kg weight not to exceed 75 grams
Adults- 75 grams Pregnants- 1hr screening= 50grams, 3hr confirmatory= 100grams NOTE- don't administer glucose challenge load to anyone with a significantly elevated FBS level |
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Limitations to OGTT
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Only limitation is the patient's ability to absorb glucose
-Any form of malabsorption will cause erroneous results - If patient has malabsorption Intravenous glucose tolerance test must be substituted |
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Explain random urine glucose test
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-Most people have a glucose threshold of about 160-180mg/dL which means if blood glucose is less that 160 than no glucose should be found in the urine.
-If glucose is found blood glucose is assumed to be over 160. - This is a POOR test because about 5% of the population has a threshold below 160 - Test is not specific for DM |
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Explain FBS test
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- Useful screeing test for all CHO disorders
- Following a 12hr fast the blood glucose reflect the interaction of insulin production and glucagon production |
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Explain 2hr Postprandial Test
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-quick and dirty screen
- if abnormal an OGTT may still be needed - Patient eats a regular mixed meal and 2 hrs later glucose is measured - If glucose is greater than 200mg/dl it is diagnostic of DM - Main problem is that the sugar challenge is NOT STANDARDIZED |
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Explain glycosylated Hgb test
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-Useful test for ALL CHO disorders
- Also called Hemoglobin A1-c and Glycated Hemoglobin - DOES NOT measure blood glucose but it estimates what the patients glucose level has been for the PREVIOUS 4-6 WEEKS. -Sort of a TIME AVERAGED glucose value - >9%= glucose has been running high - <5%= hypoglycemic - Not specific for DM but useful for monitoring - No patient prep, and fasting is not necessary |
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Explain Serum Fructosamine Test
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- Almost same thing as Glycosylated Hgb.
- Gives a TIME-AVERAGED estimate of what the glucose has been over the last 7-21 days - Useful because physician can detect change in therapy in only a week - If patient has been hyperglycemic they will have an ELEVATED fructosamine - Fructosamine is DECREASED if patient has been hypoglycemic - Test actually measures Glycosylated Albumin |
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Explain Insulin Assay
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- Done to distinguish between Type 1 and Type 2
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Explain C-peptide assays
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- Like insulin C-peptide is a product of PROINSULIN
- used for patients who are type-2 and are being TREATED WITH INSULIN INJECTIONS - Gives an advantage for type-2 patients that have developed autoimmune antibodies against insulin - 3rd advantage is C-peptide has a LONGER BIOLOGICAL HALF-LIFE compared to insulin |
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Criteria for GDM confirmatory Test
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-3HGTT. GDM is confirmed if any 2 of the following limits are exceeded
1. FBS greater than 105 mg/dl 2. 1hr >190 mg/dl 3. 2hr >165 mg/dl 4. 3hr >145 mg/dl |
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explain xylose tolerance test
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-Done to confirm INTESTINAL MALABSORPTION
- Patient empties bladder and is given 25 grams of Xylose - begin collecting a 5 hour urine - After 5 hours measure urine volume and urinary xylose concentration -Normal person should absorb at least 4.1 GRAMS, if xylose is low then it wasn't absorbed |
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Distinguish between Viral and Bacterial meningitis
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Viral- normal CSF glucose and lactate levels
Bacterial- Low CSF glucose and HIGH lactate levels -Normal range for CSF glucose is 40-70 mg/dL, and should be 2/3 of what the plasma glucose is |
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Explain Lactate assays and survival rates
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-used to project prognosis of burn and trauma patients
- Reference range is .5-1.9 mMol/L -Elevated but <4.5= 75% survival - Between 4.6 and 9.0= 50% survival - between 9.0 and 13.0= 10% survival - >15= 1% survival |
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Normal values for FBS serum and CSF
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serum- 70-110 mg/dl
CSF- 40-70 mg/dl or 2/3 serum levels |
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Normal values for Hg A1-c
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5-9%
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Normal values for OGTT
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Fasting- 70-110
1/2 hour- <170 1 hr- <170 2 Hr- <110 3-5 hours- fasting level |
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Critical values for serum or plasma glucose in kids and adults
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Below 40 mg/dl- brain damage
Above 450 mg/dl- diabetic coma |
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Critical values for serum or plasma glucose for newborn- 6 weeks
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Below 30 mg/dl- brain damage
Above 300 mg/dl- diabetic coma |
