Electrolytes/Acid-Base Balance

____ is measured based on the number of solutes per kilogram of solvent (expressed as millimoles), mOsm for convenience.

osmolality

_____ is measured in moles of solute per liter water and is less accurate in the presence of hyperlipidemia and proteinemia (in urine specimens), or in the presence of ethanol or mannitol.

osmolarity

_____ is related to several changes in the properties of a solutions relative to pure water:

• increased osmotic pressure

• lowered vapor pressure

• increased boiling point

• decreased freezing point

osmolality

the following are _____ properties:

• increased osmotic pressure

• lowered vapor pressure

• increased boiling point

• decreased freezing point

colligative

for osmolality, major contributors include Na, Cl, and HCO3. what percent is Na?

50%

for ____, minor contributors include BUN, glucose, organic substances (ethanol, methanol when present).

osmolality

osmolality is measured in biologic fluids. true or false?

true

osmolarity is measured in biologic fluids. true or false?

false

serum osmolality is _____ in the following:

• DM

• renal diseases

• ETOH

• MetOH poisoning

increased

serum osmolality is _____ in the following:

• MI

• shock

decreased

urine osmolality is _____ in the following:

• fluid restriction

• DM

increased

urine osmolality is _____ in the following:

• overhydration

• diabetes insipidus

• chronic renal failure (CRF)

decreased

osmolality in plasma is important because it is the parameter to which the _____ responds.

hypothalamus

a small change in plasma osmolality will activate thirst receptors and ____ secretions

ADH

another term for ADH is _____.

AVP

what is the reference interval for serum osmolality (in mOsm) that MUST be maintained at all times?

275-295

a 1-2% increase in osmolality that causes a fourfold increase in the circulating concentration of ____.

AVP

a 1-2% decrease in osmolality shuts off ____ production.

AVP

osmolality can be measured in serum or urine but not ____.

plasma

the most common instrument for osmolality testing is the ____.

osmometer

what refers to the difference between measured and calculated osmolality?

osmolal gap

what indirectly indicates the presence of osmotically active substances other than Na, urea, or glucose (e.g., ethanol, methanol, ethylene glycol, isopropanol, lactate, or b-hydroxybutyrate)?

osmolal gap

what is the equation for the calculated osmolality?

(1.86 x Na) + (Glu / 18) + (BUN / 2.8) + 9

osmolal gaps are ____ in the following:

• ketoacidosis

• renal tubular acidosis (RTA)

• lactic acidosis

• methanol, ethanol, anti-freeze poisoning

increased

serum osmolality reference interval in mOsm/Kg:

275-295

urine (24) osmolality reference interval in mOsm/Kg:

300-900

serum/urine ratio reference interval:

1.0-3.0

random urine osmolality reference interval in mOsm/Kg:

50-1200

osmolal gap reference interval in mOsm/Kg:

5-10

concentration of electrolytes must be tightly controlled within a narrow range. true or false?

true

sodium is a major extracellular cation. true or false?

true

____ is found 30% in bones and 70% in fluids.

sodium

sodium is _____ in these situations:

• renal loss

• GI loss

• skin loss

• insufficient intake

decreased

sodium is _____ in serum in these situations:

• congestive heart failure (CHF)

• cirrhosis

• normal saline (NS): generalized edema

decreased (diluted)

hypertonic refers to ____ osmolality.

increased

hypotonic refers to ____ osmolality.

decreased

_____ hyponatremia is associated with marked hyperglycemia and mannitol therapy.

hypertonic

_____ hyponatremia is associated with:

• hypovolemic: renal sodium loss or extrarenal route

• euvolemic: SIADH, psychogenic polydipsia

• hypervolemic: CHF, NS, cirrhosis

hypotonic

_____ hyponatremia is associated with an increase in non-sodium cations (e.g., severe hyperkalemia, severe hypercalcemia, and increased y-globulins such as in multiple myeloma).

normotonic

_____ refers in increased sodium caused by:

• high diet intake

• IV infusion

• Conn syndrome

hypernatremia

potassium is a major extracellular cation. true or false?

false

potassium is mostly in ____ cells.

muscle

what cation is freely filtered by the glomeruli with a majority is reabsorbed by the proximal tubule then secreted in the distal tubule?

potassium

potassium is decreased in ____ loss:

• hyperaldosteronism (urine potassium is high —> secretion to urine): Conn syndrome

• diuretics

• hypomagnesemia

• RTA I and II

renal

potassium is decreased in ____ loss:

• urine potassium is low

• vomiting, diarrhea

GI

hypokalemia is associated with transcellular shifts such as _____.

metabolic alkalosis

hyperkalemia is associated with ____ in all cases except RTA I and II.

acidosis

pseudo-hyperkalemia is most often caused by ____.

hemolysis

potassium is ____ in:

• therapeutic K+ administration

• insulin deficiency

• acute renal failure (ARF)

• hypoaldosteronism

increased

what is the anticoagulant of choice for sodium and potassium samples?

lithium heparin

sodium and potassium samples are stable for _____ at 0-6°C.

1 week

sodium and potassium samples are stable for _____ at -20°C.

1 year

chloride is a major extracellular anion. true or false?

true

_____ is important in maintaining anion-cation balance (electroneutrality).

chloride

what anion is freely filtered with passive reabsorption in proximal convoluted tubules (alone with Na), and active reabsorption in ascending loop of henle?

chloride

what electrolyte is measured in sweat and increase is diagnostic of cystic fibrosis?

chloride

chloride is ____ in:

• prolonged vomiting

• DKA

• aldosterone deficiency

• salt-losing renal diseases such as pyelonephritis

• compensated respiratory acidosis or metabolic alkalosis

decreased

chloride is ____ in:

• dehydration

• RTA

• metabolic acidosis

• high salt intake

increased

a major component of total CO2 in plasma as ____ (>90%).

HCO3

_____ is part of the bicarbonate-carbonic acid buffering system.

HCO3

bicarbonate is almost completely reabsorbed in the ____.

renal tubules

bicarbonate is ____ in:

• excess ingestion of antacids

• renal overcompensation for respiratory acidosis

increased

bicarbonate is ____ in:

• diarrhea

• metabolic acidosis

• renal overcompensation for respiratory alkalosis

decreased

what analytical method of bicarbonate refers to CO2 from the sample being diffused through a semipermeable membrane into an electrolyte solution where pH changes are measured?

modified pH

for bicarbonate specimens, specimens must be kept capped. true or false?

true

what refers to the calculation of the difference between measured anions and cations?

anion gap

what equation is used to calculate anion gap?

Na - (Cl + HCO3)

what is the reference interval for anion gap?

7-16

a large ____ may be indicative of excess unmeasured anions such as PO4 and SO4 (as in uremia/renal failure), organic acids, lactic acid, methanol poisoning, salicylate poisoning, and instrument error!)

anion gap

the minerals calcium and phosphorus are present in the bone in the form of _____.

calcium phosphate crystals

what form of calcium refers to a bound form, 45-50% total Ca bound to albumin?

non-diffusible

what form of calcium refers to free (ionized), physiologically active form and can cross blood-brain barrier?

diffusible

total calcium can be low in hypoalbuminemia but free (ionized) is ____.

normal

_____ may present with lethargy, hyporeflexia, nausea, vomiting, etc. with increase risks of pancreatitis and peptic ulcers.

hypercalcemia

_____ causes neurologic excitability, hyperreflexia, periorbital tingling (paresthesia), and muscle spasms.

hypocalcemia

calcium is ____ in:

• hyperparathyroidism: high secretion of PTH

• hypervitaminosis D

• multiple myeloma: CRAB syndrome

increased

calcium is ____ in:

• classic chvostek and trousseau signs

• in severe cases may lead to tetany and respiratory arrest

• hypoparathyroidism

• decreased absorption: steatorrhea

• nephrosis: excess protein loss

decreased

phosphorus is ____ in:

• hypoparathyroidism: low secretion of PTH

• hypervitaminosis D

• renal failure

increased

phosphorus is ____ in:

• hyperparathyroidism

• ricketts

• fanconi syndrome

• absorption problems: sprue and celiac disease

decreased

_____ hyperparathyroidism causes renal disorders with irreversible damage to the kidneys.

primary

_____ hyperparathyroidism caused by renal disorders (which increase serum phosphorus and lower serum calcium, which in turn causes increased PTH).

secondary

what condition is associated with:

• iatrogenic

• due to thyroidectomy (most common cause)

• decreased urinary excretion of phosphorus (hence increased serum phosphorus)

• decreased 1,25(OH)₂ (calcitriol) level

hypoparathyroidism

calcium and phosphorus samples cannot be collected in oxalate, citrate, or EDTA. true or false?

true

____ testing for urine should be acidified with 6mol/L HCl (1mL HCl in 100mL urine) before analysis.

calcium

hemolyzed samples are acceptable for phosphorus testing. true or false?

false

circulating phosphate levels are subject to ____, with highest levels in late morning and lowest in the evening.

circadian rhythm

urine analysis for ____ requires 24 hour sample collection because of significant diurnal variation.

phosphorus

____ acids refers to CO2 (around 20 mol/d by normal metabolism), can be removed by the lungs.

volatile

_____ acids refer to uric acid, phosphoric acid, sulfuric (around 100mmol/d by normal metabolism).

non-volatile

_____ acids cannot be removed by the lungs, must be excreted through the kidney.

non-volatile