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BUN levels indicate

how well liver is functioning and how well kidneys are excreting

critical BUN level

over 100

decreased BUN in

liver disease, fluid overload, malnutrition / malabsorption, early pregnancy, nephrotic syndrome

increased BUN in

high protein diet, UGI bleed, steroids, tetracycline, azotemia

prerenal azotemia causes

hemorrhage, shock, trauma, sepsis, high protein diet, tumors, dehydration

causes of postrenal azotemia

urethral obstruction

better measure of kidney fx than BUN

serum creatinine

why serum creatinine would be elevated


look for prerenal cause if BUN / creatinine ratio is above


complete metabolic profile includes

basic metabolic profile and liver fx tests

factors that can influence metabolic profile results

hemolysis, timing, lab error

critical serum creatinine value


critical sodium values

<120 or >160

importance of sodium

Major extracellular cation , maintains ECF (extra cellular fluid) volume

most common electrolyte disturbance in hospitalized pts


hyponatremia is asx until sodium drops below

125 mEq/L weakness

neuro sx of hyponatremia show up when levels drop below

115 mEq/L thirst hyperreflexia

predominant intracellular cation


serum potassium depends on

aldosterone, sodium reabsorption, acid base balance

aldosterone's effect on K

increases renal loss of K

effect of sodium reabsorption on K

K lost as Na reabsorbed

K levels in alkalosis


K levels in acidosis


EKG changes that correspond to K changes

hypoK - prolonged PR, depressed ST, prominent U, hyperK - wide qrs, peaked T

reasons for pseudohyperkalemia

hemolysis, tourniquet too tight, needle bore too small

major extracellular anion


chloride follows

Na (attempts to maintain electrical neutrality)

normal anion gap

8 - 12

anion gap calculation

AG= Na - Cl +CO2 (represents unmeasured anions, i.e. sulfate, phosphate, protein, organic acids not routinely measured)

majority of magnesium found in

bone (20% found in muscle)

hypomagnesia often seen in


sx of hypocalcemia

tetany, Chvostk's sign, trousseau's sign, muscle cramps, seizures, dysrythmias, prolonged QT

Chvostek's sign

tap TMJ and face twitches

Trousseau's Sign

reflexive hand spasm when BP cuff is pumped too high

glucose levels are controlled by

insulin and glucagon

indications of diabetes

fasting BS >126 on more than one occasion or random >200 once with clinical symptoms, GT testing >200 at 2 hours

Hg A1C

(screening test for diabetes) marker of glucose levels over past 3 months

Glucose tolerance test

not used in screening test - used in high risk individuals who are already suspected of having diabetes

abnormal glucose tolerance test

persistent elevated 2 hr levels (>200 mg/dL)

usual cause of hypoglycemia

insulin overdose

definition of hypoglycemia

blood sugar <50 mg/dL with symptoms

reason for fasting and postprandial hypoglycemia

fasting - pathological, postprandial - exaggerated insulin response

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