BF and Electrolytes- Biochemistry 1

Sodium functions

Electrolyte balance, water distribution between intra/extra cellular spaces a/w BP

Required for nerve impulse transmission (CNS) and muscle contractions

Symptoms of Hyponatremia are primarily due to

hypotonicity causing cerebral edema

Why does an indirect ISE cause a lower looking sodium level

Because the analyzer assumes plasma is 93% water—> but in these cases, water % is less so Na looks lower 

What does isotonic (pseudo) hyponatremia do to the osmolal gap

It increases it, but measured serum osmolality is normal

Hypotonic hyponatremia serum osmolality

Low serum osmolality.

Hypovolemic hypotonic hyponatremia definition

Total Na⁺ loss is greater than H₂O loss.

Renal causes of hypovolemic hypotonic hyponatremia

High urine Na⁺; due to diuretics or low aldosterone (Addison’s disease).

Extra-renal causes of hypovolemic hypotonic hyponatremia

Low urine Na⁺; GI losses (vomiting/diarrhea) or sweating followed by hypotonic fluid replacement (e.g., marathon deaths).

Euvolemic hypotonic hyponatremia causes

Normal Na⁺ with increased H₂O; SIADH, psychogenic polydipsia, hypothyroidism.

Hypervolemic hypotonic hyponatremia causes

Increased Na⁺ but even greater increase in H₂O; CHF, cirrhosis, nephrotic syndrome.

Hypertonic hyponatremia serum osmolality

High serum osmolality.

Mechanism of hypertonic hyponatremia

High osmotically active substances pull water into blood → dilutes plasma Na⁺ → low Na⁺.

Endogenous causes of hypertonic hyponatremia

Extreme hyperglycemia, uremia.

Exogenous cause of hypertonic hyponatremia

Mannitol infusion (e.g., for lowering intracranial pressure).

Hypernatremia

High Serum [Na+]

When does hypernatremia occur

When body Na+ is in exces compared to body water, always a/w and increase in plasma osmolality

Hypernatremia can result in an increase in

BV/BP

What are the effects of hypernatremia caused by osmosis

Water is drawn out of the cells, esp in the brain, causing them to shrink

Symptoms of hypernatremia

CNS hyper-osmolar state

What are the two major causes of Hypernatremia

Fluid deficit- more common

Excess total body Na+

How does a fluid deficit cause hypernatremia

Dehydration -most common

H2O loss causing DI

How does excess total body Na+ cause hypernatremia

The primary cause is IV hypertonic saline use

or and increase in renal conservation(hyperaldosteronism)

Functions of potassium

Regulation of neuromuscular excitability

contraction of heart muscle 

Why is potassium measured

to ID cause or monitor treatment of hyperkalemia (kidney dz is most common or metabolic acidosis-DKA)

Potassium plasma levels are regulated by

Kidney function(aldosterone, drugs(diuretics)

Exchange between cell and plasma

(Na-K-ATPase pump)

and blood pH( K and H ions exchange across cell membranes, causing acidosis (DKA or lactic acidosis) which in turn causes an increase in plasma [K+]

Hypokalemia is when K+ is below what range

below 3.4

What are the effects of hypokalemia 

muscle cramps 

fatal cardiac arrythmias or arrest when below 2.5

What are the major causes of hypokalemia

-True K+ deficit

renal loss causes an increase in urine K+ (hyperaldosteronism or drugs (K-wasting diuretics)

extra renal losses causes a decrease in urine K+

-Redistribution : metabolic alkalosis or treatment of DKA 

Hyperkalemia is when K+ is more than what range

5.0

Effects of hyperkalmeia

Cardiac failure when it goes above 6.5

What are the major causes of hyperkalemia

-An increase in total body K+- impaired renal excretion : renal failure (aldosterone decreases)

-Redistrubition (causing acidosis, or hemolytic anemia)

-Pseudohyperkalemia

In potassium measurement, improper collection and handling can cause 

a false high 

what types of improper collection cause potassium levels to appear higher 

traumatic collection (hemolysis), prolonged tourniquet application, vigorous mixing, wrong anticoagulant (K2-EDTA)

what types of improper handling cause potassium levels to appear higher 

Refrigeration causing delayed seperation from cells

chloride functions

maintains electrical neutrality, and fluid acid-base balance

How is chloride regulated

passively reabsorbed by renal PCT and DCT

distribution of Cl between plasma and RBC changes as function of HCO3-(Cl- shift) maintaining the buffering capacity of blood.

Direct causes of hypochloremia

loss of Cl (vomiting, addisons Dz)

Indirect causes of hypochloremia

metabolic alkalosis (high plasma HCO3- causing an increase in chloride shift into cells)

Hyperchloremia is caused by

dehydration or excess loss of HCO3- (diarrhea)

Cystic fibrosis is caused by

CFTR gene mutation

Cystic fibrosis cause an increase in the secretion of

NaCl which causes an overly thick mucus

What are the effects of an overly thick mucus

Lungs- plugging airways causing bacterial and fungal infections

pancreas- plugging ducts blocking release of digestive enzymes

intestine- blockage of stool passage 

What is HCO3- function

Main component of the bicarbonate-carbonic acid buffering system that maintains blood pH

How is HCO3- regulated

Kidneyes filter and reabsorb HCO3- to regulate acid base balance

if blood is alkalotic what happens to HCO3-

it is excreted by the kidney

if blood is acidotic what happenes to H+ and HCO3-

H is excreted and HCO3- is reabsorbed

Why is HCO3- measured

screens for acid-base D/Os or monitors their treatment

Hypobicarbonate value & meaning

↓ HCO₃⁻ (< 20 mmol/L); metabolic acidosis.

Causes of metabolic acidosis: increased endogenous acids

Ketoacids, lactic acid, phosphoric acid → anion gap ↑.

Causes of metabolic acidosis: toxic ingestions

Salicylate, ethylene glycol, methanol → anion gap ↑.

Metabolic acidosis from decreased renal acid excretion

Hypoaldosteronism (Addison’s disease) → normal anion gap.

Metabolic acidosis from bicarbonate loss

Chronic diarrhea; renal overcompensation for respiratory alkalosis → normal anion gap.

Hyperbicarbonate value & meaning

↑ HCO₃⁻ (> 30 mmol/L); metabolic alkalosis.

Causes of metabolic alkalosis: increased renal acid excretion

Hyperaldosteronism (Conn’s syndrome); Cushing syndrome.

Lactic acid: what it is

Acidic end-product of anaerobic glucose metabolism.

Where lactic acid is produced

RBCs, muscle, brain, and gut.

Lactic acid as a clinical indicator

Early and sensitive indicator of tissue hypoxia (levels ↑).

Regulation of lactic acid

Not specifically regulated; rises quickly when oxygen delivery drops below a critical level.

Clinical uses of lactic acid measurement

Used to monitor critically ill patients; increased in leukemia, liver failure, kidney disease, infections, MI, CHF, and diabetes.

Toxins that increase lactic acid

alcohol (EtOH), methanol, salicylates.

Lactic acid specimen requirement:

NaF
Use sodium fluoride to inhibit glycolysis.

Lactic acid specimen requirement:

tourniquet
Avoid using a tourniquet—venous stasis can falsely increase lactate.

Lactic acid specimen handling:

temperature
Keep specimen on ice to prevent false increases at room temperature

Lactic acid specimen handling: processing

Separate the sample as soon as possible.

Lactic acid testing methods

Common enzymatic methods that produce colored dyes; ISE methods also used.

Normal lactate reference range

0.7–1.3 mmol/L.

How is anion gap calculated

(Na + K) - (Cl + HCO3)- normal 10–20 mmol/L

or Na - (Cl +HCO3)- normal 6–16 mmol/L

Electrical neutrality of blood

Total cations = total anions, but not all ions are measured.

What the anion gap reflects

Amount of unmeasured ions in the blood.

Why it's called the “anion gap”

The unmeasured ions are mostly anions.

Clinical use of anion gap

Helps detect increases in unmeasured anions in plasma.

Why anion gap exists 

Electroneurtrality required 

routinely meadure more cations than anions 

Anion gap significance

Helps distinguish between anion gap vs non anion gap metabolicacidosis 

Why AG increases in AG metabolic acidosis

Drop in HCO₃⁻ increases the calculated anion gap

Why AG stays normal in NAGMA

Loss of HCO₃⁻ is compensated by ↑ Cl⁻ → anion gap remains ~normal.

Electrolyte specimen types

Serum; whole blood or plasma (lithium heparin).

Artifactual electrolyte change: passive transfer

IV fluid contamination → falsely increased electrolytes.

Artifactual electrolyte change: anticoagulant contamination

Incorrect tubes (Na-citrate, Na-heparin, K-EDTA, NaF, K-oxalate) can falsely increase electrolytes.

Artifactual electrolyte change: hemolysis

Releases K⁺, Mg²⁺, and PO₄³⁻ → false increases.

Artifactual electrolyte change: delayed separation

K⁺ ↑, Na⁺ ↓, HCO₃⁻ ↓.