Critical care Analytes and Electrolytes & water balance

1. Critical care Analytes
Electrolytes & water balance
Dr. Elham Sharif,PhD
Assistant professorof BiomedicalSciences
College of Health Sciences
Qatar University
Tel: 00974-4403-4788
Email: e.sharif@qu.edu.qa

2. Objectives
• After attending two lectures on electrolyte balance, the students will:
• Define/Identify electrolyte, osmolality, anion gap, anion, and cation. (TL1)
• Assess the clinical significance of each of the electrolytes mentioned in this
unit. (TL1)
• Calculate osmolality, osmolal gap, and anion gap and discuss the clinical
• usefulness of each. (TL3)
• Recommend the analytic techniques used to assess electrolyte
concentrations.
• Correlate the information with disease state, given patient data. (TL3)
• Identify/Recall the reference ranges for sodium, potassium, chloride,
bicarbonate, magnesium, and calcium. (TL1)
• Evaluate/Identify the specimen of choice for the major electrolytes. (TL3)
• Assess the usefulness of urine electrolyte results: sodium, potassium,
calcium, and osmolality. (TL3)
• Correctly interpret laboratory results when given a set of laboratory data and
patient history. (TL3)
2Dr Elham Sharif

3. Introduction
• The tests involving: Na+, K+, Cl-, HCO3
-, pH, partial
pressure of CO2 (PCO2), (PO2), osmolality are
considered as critical care analytes for several reasons:
o Used to monitor patients in critical care settings in ICU,
emergency room & operation room.
o Results are needed quickly to speed up the treatment.
Glucose, ionized Mg and coagulative tests (prothrombine time [PT]/
partial thromboplastin time [PTT) are also regarded as ctirical
care analytes
3Dr Elham Sharif

4. Sodium balance
• Most NaCl intake added during food preparation
• Sweat output depends on body temperature
• Urine output of NaCl is regulated by blood pressure
4

5. Water balance
• Metabolically produced by oxidation of H-containing nutrients
• Insensible loss: expiration of 37 saturated air, evaporation through skin (different
from sweat)
• Urine output regulated by ( ADH)
5

6. • Macula densa: specialized cells in wall of distal tubule
• Juxtaglomerular cells (Granular cells): contain renin.
Juxtaglomerular apparatus
6

7. Forces of filtration
7

8. • Substance X: filtered & entirely secreted (rare)
• Substance Y: filtered & partially reabsorbed (Na+, K+, water)
• Substance Z: filtered & entirely reabsorbed (glucose, amino acids)
Kidney handling of various substances
8

9. Osmolality and volume regulation
A. biochemistry and Physiology
• All ions & neutral solutes contribute to plasma osmolality.
• Size & charge of molecule has little effect on osmolality because, it depend
on the number of particles in solution.
• Thus each molecule of albumin, glucose, alcohol or urea contribute equally.
• Measuring serum and urine osmolality is useful in assessing
electrolyte disorders and acid-base status. Major molecules measured
by serum osmolality include sodium, chloride, glucose, and urea.
(update)
• Definition of colligatative properties: it’s a property of a solution that is
influenced by size and shape of the molecules, but not individual
composition.
• There are 4 types of colligative properties: boiling point, freezing point,
osmotic pressure & vapour pressure.
9Dr Elham Sharif

10. Osmolaity defintions
• Osmosis: water flow across a semi-permeable membrane.
• Molality: the number of moles of solute per Kg of water
• Osmolality: the number of moles of particles per kg of water, expressed as
osmoles per kilogram of water.
o Serum osmolality is expressed as milliosmoles/kg; the reference range
for serum is 275-295 mOsm/kg. (update)
• Osmolarity: defined as the number of osmoles of solute/L of solution
(osmol/L or Osm/L).
• Osmometry: measuring all particles of osmolality of a solution.
• Osmolality is regulated by the hypothalamus through the sensation of thirst
and the signaling to secrete antidiuretic hormone (ADH).
o When the osmolality of the blood is increased, two processes
occur:
o 1) Consuming more water will decrease the osmolality.
o 2) Posterior pituitary secretion of ADH will cause renal reabsorption of
water and decrease the osmolality. (update)

11. • Calculated osmolality (mOsm/kg)=
2[Na+] +[BUN(mg/dL)/2.8] + [glucose (mg/dL)/18]
• In healthy individuals, the calculated osmolality equals the
measured osmolality. (update)
• Osmolal gap = is the difference between the measured
osmolality and the calculated osmolality.
o Osmolal gap = the measured osmolality - the calculated
osmolality.
o A normal osmol gap is < 10 mOsm/kg
o The osmolal gap indirectly indicates the presence of osmotically
active substances other than Na+, urea, or glucose, such as
ethanol, methanol, ethylene glycol, lactate, or β-hydroxybutyrate.
o Therefore it is used to test alcohol, in person’s who has ingested
toxins or alcohol,

12. Case: The following results are obtained from a 32-year-
old diabetic patient:
• Analytes Results RI
• Na 138 mmol/L (136-145)
• K 4.2 mmol/L (3.5-5)
• Cl 100 mmol/L (99-109)
• Glucose 234 mg/dL (70-105)
• BUN 28 mg/dL (10-20)
• Serum osmolality 345 mOsml/k ( 275-295)
Based on this data, Calculate the patient’s osmolal gap?
Dr Elham Sharif 12

13. Case answer: mOsmol/kg
• Calculated serum osmolality (mOsm/kg) =
• 2[Na+] +[BUN(mg/dL)/2.8] + [glucose (mg/dL)/18]
= (2 x 138) + (28/2.8) + (234/18) =
= 276 + 10 + 13 = 299 mOsml/kg
•
• Osmolal gap (OG) = measured osmolaity – calculated
osmolality
• Osmolal gap (OG)= 345 – 299 = 46 mOsmol/kg
Dr Elham Sharif 13

14. infusion of saline solutions of different osmolalities on the
volumes and osmolalities of various body fluid spaces.
EC vol. IC vol. EC osm. IC osm.
Isotonic saline
Water
Hypertonic Saline
Hypotonic saline
14
Dr Elham Sharif

15. Regulation of osmolality (RO) & blood volume
• Osmolality in plasma is the parameter to which the
hypothalamus respond
• The RO indirectly affects the Na conc. in plasma, because Na
& its associated anions account for 90% of osmolality in
plasma.
• The regulation of blood volume also affects Na conc. in blood.
• Osmolality and volume, although regulated by separate
mechanisms, are related because:
o Osmolality (Na) is regulated by changes in water
balance,
o Whereas volume is regulated by changes in Na balance.
15Dr Elham Sharif

16. Hormones of Water and Sodium
Regulation
• Angiotensin-II
• Anti-diuretic hormone/vasopressin/ADH/AVP
• Aldosterone
o  Na+ channel activity
o  K+ channel activity,
o  Na+/K+ ATPase pump
• Atrial natriuretic peptide (ANP)
16Dr Elham Sharif

17. harif

18. Renin angiotensin aldosterone system
18

19. Renin angiotensin aldosterone system on Na+ excretion
19

20. Atrial natriuretic peptide (ANP) on Na+ excretion
ANP actions:
1.  Na+ reabsorption from deep
medullary collecting duct
2.  glomerular filtration rate
Both actions  Na+ excretion
20Dr Elham Sharif

21. 1. Regulation of osmolality
Normal
• Normal plasma osmolality: 275-290 mOsm/kg of plasma H2O.
• Plasma osmolality is maintained by process involving:
o Thirst & ADH (vasopressin).
o ADH is secreted by the hypothalamus, acts to ↑ reabosrption of
water in the CT, its half life is 15-20 minutes.
o Osmo-receptors in the hypothalamus respond quickly to small
changes in osmolality;
• 1-2% ↑ in osmolality causes a 4-fold ↑ in the circulating
conc. Of ADH
• But 1-2% ↓ in osmolality shuts off ADH production.
21Dr Elham Sharif

22. Factors affecting ADH release
22
Dr Elham Sharif

23. Summary: Vasopressin (ADH) release & actions
Vasopressin release stimulated by:
1. slight (1%) increase in plasma osmolality
2. large (~10-15%) reduction in plasma volume
Vasopressin action:
increases permeability of collecting duct to water
Renal medulla
has osmotic gradient from 300 mOsm/kg at cortical border to 1200 mOsm/kg
at deepest part of medulla
 ADH levels  collecting duct permeability  water reabsorption 
urine volume with  osmolality
23Dr Elham Sharif

24. Regulation of thirst
Sensation of thirst stimulated by:
• 1%  osmolality
• >10-15%  blood volume
•  angiotensin II
24Dr Elham Sharif

25. 2. Regulation of blood volume BV
• Normal blood volume is essential to maintain blood pressure and
ensure perfusion of blood to all tissues and organs.
• If blood volume decreases, the renin-angiotensin-aldosterone
system (RAAS) respond to decrease renal blood flow as follows:
o (i.e ↓ BV & or↓BP) by secreting renin in the renal glomeruli.
o Then renin converts angiotensinogen to angiotensin I, which is then
converted to angiotensin II in the lungs.
o Angiotensin II causes:
• vasoconstriction which ↑s BP &
• secretion of aldosterone which ↑s renal retention of Na and H20
25Dr Elham Sharif

26. Copyright2005WadsworthGroup,adivisionofThomsonLearning
How The Body Regulates Blood Volume and therefore
blood pressure: Responses to reduced blood volume:
26
DrElhamSharif
Angiotensin II

27. Responses to a decreased blood volume:
• Volume respecters & thirst sensation stimulate both thirst
and release of ADH independently of osmolality.
• Secretion of epinephrine and norepinephrine.
• Production of angiotensin II, leading to vasoconstriction,
increased renal reabsorption of Na and release of
aldosterone.
• Secretion of aldosterone, promotes distal tubular
reabsorption of Na and Cl- in exchange for K+ & H+.
• Decreased GFR due to volume depletion.
27Dr Elham Sharif
Regulation of blood volume

28. Responses to an increased blood
volume:
• Release of atrial natriuretic peptide (ANP) from the
myocardial atria, promoting Na excretion by the kidney.
• Increased GFR due to volume expansion.
• Even 1-2% reduction in tubular reabsorption of Na can
increase H20 loss by several litres per day.
28Dr Elham Sharif
Regulation of blood volume

29. Abnormal/Excess H20
• Excess H2O intake → plasma osmolality ↓ this → suppression
of ADH secretion & thirst.
• Excess water intake lead to hypo-osmolality & hyponatremia
almost only in patients with impaired renal excretion of water.
29Dr Elham Sharif
Regulation of osmolality

30. Water Loading
Drink Water
Plasma Osmolality
Activation of osmoreceptors in
the hypothalamus
ADH secretion from Post. Pituitary
Water permeability in late DT and CT
Water Reabsorption
Urine Osmolality Urine Volume
30
Dr Elham Sharif

31. Abnormal/ Inadequate H20
• Less water intake → ↑ in plasma osmolality, activatingADH
secretion & thirst.
• ADH minimizes renal water loss, while thirst motivates water
drinking normally.
• Hypernatremia may occur in:
o Infants, unconscious pts, or starvation
o Over 60 yrs, osmotic stimulation of thirst is diminished,
dehydration is more likely in older patients with illness and
mental status.
o Patients with diabetes insipidus DI (no ADH), may excrete10 L
of urine/day, but since thirst persists, water intake matches
output and plasma Na remain normal, an example of the
effectiveness of thirst in preventing dehydration.
31Dr Elham Sharif
Regulation of osmolality

32. Water
Deprivation Drink Water
Plasma Osmolality
Activation of osmoreceptors in
the hypothalamus
ADH secretion from Post. Pituitary
Water permeability in late DT and CT
Water Reabsorption
Urine Osmolality Urine Volume
32
Dr Elham Sharif

33. Urine osmolality
• Varies widely
• Depending in H2O intake & time of collection
• Generally decreased in DI (no ADH) & polydipsia
(chronic thirst)
• Increased in SIADH & hypovolemia (↓ed urinary Na)
33Dr Elham Sharif

34. Methods for measuring osmolality
A. Urine osmolality: can measure the kidney ability to concentrate ions and
indirectly kidney function.
o Measure ions measured by osmolality include electrolytes, glucose & urea.
B. Serum osmolality is compared to urine osmolality.
C. Colloid osmotic pressure: measures only the effect on osmolality by large,
essential proteins, used to detect conditions leading to pulmonary oedema.
D. Freezing point depression principle: solutions cool then expend when
freeze.
- by freezing point, one can determine the amount of particles in that
solution based on the freezing curve.
e. Vapour pressure: can be also used to measure osmolality
- surface molecules in a liquid are in motion, escaping molecules form a
vapour above the liquid that is in equilibrium with liquid molecules.
34Dr Elham Sharif

35. Electrolytes: Sodium, Potassium, Chloride, and
Total Carbon Dioxide
• Electrolytes: charged ions that are found in ICF, ECF and interstitial fluid.
• Intracellular fluid ICF: inside the cells and contain mostly potassium ions
• Extracellular fluid ECF: outside the cells and contain mostly Na ions.
• Cations: positively charged ions, major cations in the body are Na, K, Ca,
Mg
• Anions: negatively charged ions, major anions in the body are Cl, HCO3,
HPO4,SO4, organic acids and proteins.
• Clinically, when electrolytes are ordered on an individual, the term
"electrolytes" is understood to mean the measurement of serum
sodium, potassium, chloride, and total carbon dioxide (bicarbonate).
The serum concentration of these four electrolytes is quantified using
ion-selective electrodes (ISEs). (update)
35Dr Elham Sharif

36. Electrolyte Concentration
• Expressed in milli-equivalents per litre (mEq/L), a
measure of the number of electrical charges in one litre
of solution.
• Milli-equivalents per litre (mEq/L) =
(concentration of ion in [mg/L] ÷ the atomic weight of ion)
× number of electrical charges on one ion.
36Dr Elham Sharif

37. Sodium Na+
• Major cation of ECF (90%)
• Normal range:135-145mEq/L
• Na conc. 15-fold > in ECF than ICF
• To maintain this gradient, an active transport system involving a
NA+- K+- ATPase pump moves 3 Na ions to ECF in exchange for
moving 2 K+ions into cells.
• Changes in sodium result in changes in plasma volume.
• Largest constituent of osmolality.
• Helps maintain acid base balance through Na-H pump.
• Works to excite nerves and muscles
• Regulation: Na is regulated by reabosorption in the proximal
convoluted tubules by aldosterone.
37Dr Elham Sharif

38. Reference ranges for Na, osmolality, K+, Cl-,
total CO2 and anion gap
135-145 mmol/LNa, plasma
Osmolality, plasma
275-295 mOsm/kgChildren & adults
280-300 mOsm/kgAdults> 60yrs
300-900 mOsm/kgUrine osmolality(24hr collection)
3.5-5.0 mmol/LPotassium, plasma
98-107 mmol/LChloride
8-16 mmol/L [(Na+)- (Cl-+HCO3
-)]Total CO2
10-20 mmol/L [(Na++ K+)- (Cl-+HCO3
-)]Anion gap
38Dr Elham Sharif

39. 39
Dr Elham SharifRegulation

40. Pathway of RAAS
40

41. Clinical significance/Hyponatremia
1. Hyponatremia: abnormally low Na levels < 135 mEq/L, confirmed by decreased
plasma osmolality
a) Depletional hypnatremia causes:
- Diuretics
- Diarrhoea, vomiting, severe burns or trauma
- Hypoaldosteronism (Addison’s disease), adrenal insufficiency, deficiency
of aldosterone & cortisol, prevent reabsorption of Na in the distal tubule
b) Dilutional hyponatremia causes:
- Over hydration (water overload), syndrome of inappropriate antidiuretic
hormone (SIADH), CHF, cirrhosis, and nephrotic syndrome.
c) Symptoms:
- no symptoms when Na is > 125 mEq/L.
- Symptoms occur when Na < 125 mEq/L, e.g. nausea & malaise
- Na 110-120 mEq/L e.g. Headache, lethargy
- Na< 110 mEq/L lead to seizures and coma
The severity of the neurologic symptoms directly proportional to how fast the Na &
osmolality decrease
41Dr Elham Sharif

42. Hyponatremia related to volume status
Na loss in excess of H2O lossHYPOVOLEMIC
Thiazide diuretics
Loss of hypertonic fluid, GI, burns, sweat
Potassium depletion
Problem with water balanceEUVOLEMIC/NORMOVOLEMIC
SIADH
Artifactual: due to sever hyperlipidemia
Adrenal insufficiency
Excess H2O retention, causes
edema
HYPERVOLEMIC
Advanced RF (↓GFR, with ↑ H20 intake)
CHF, hepatic cirrhosis
Nephrotic syndrome
leading to vasodilation and stimulation of
ADH and thus water retention and low
blood pressure.
In pregnancy: the hypothalamus
regulate plasma Na 5 mmol > than
normal…

43. SIADH
(syndrome of inappropriate ADH secretion)
• Excessive ADH secretion
• Not “turned off” by drop in osmolality from drinking water
and water retention.
• Hyponatremia is also the main concern
• Causes
o Head trauma, Tumors, CNS disorders
o Endocrine disorders, Pulmonary conditions
o Ectopic lung tumor (secretes ADH), drugs
• Treatment – water deprivation or removal of tumor
43Dr Elham Sharif
EXAMPLE 1

44. Water transport & vasopressin actions
44

45. Excessive diuretic use (hypotonic contraction)?
Excessive loop or thiazide diuretic
↓ Na+ reabsorption DCT
↓ plasma osmolality
↓ ADH
↑ water excretion
↑ K+ excretion/
hypokalemia
(isotonic)
↓ vascular volume ↑ RAA
↑ Na reabsorption
(at principal cell)
↑ H excretion
Metabolic alkalosis
(when > 10%)
↑ ADH
↑ water retention
hyponatremia
EXAMPLE 2

46. Addison’s disease/ hypoaldseronism (hypotonic contraction)?
↓ aldosterone/glucocorticoids
↓ Na+ reabsorption (principal cell)
↓ plasma osmolality
↓ ADH
↑ water excretion
↓ K+ excretion/
hyperkalemia
(isotonic)
↓ vascular volume
↓ H+ excretion/
Metabolic acidosis
(when > 10%)
↑ ADH
↑ water retention
Hyponatremia
(osmotic response)
hypoglycemia
(pressure response)
JFK
46Dr Elham Sharif
EXAMPLE 3

47. Diabetes Insipidus
• Loss of ADH secretion or insensitivity of kidneys to ADH
• Large severely dilute amounts of urine
• Increased intake of water
• Danger lies in hyponatremia and ultimate central
nervous system edema and death.
47Dr Elham Sharif
EXAMPLE 4

48. Types of Diabetes Insipidus (DI)
• Central
o Damage to hypothalamus – no ADH
• Nephrogenic
o Kidneys cannot respond to ADH
o Usually genetic (rare) 90% cases due to V2 receptor
mutation, 10% due to Aquaporin mutation.
• Dipsogenic
o Damage to thirst center – making patient abnormally
thirsty
• Gestational
o During pregnancy women produce vasopressinase which
breaks down ADH, increasing urine output.
48Dr Elham Sharif
EXAMPLE 4 CONT’D

49. Tests for Diabetes Insipidus
• Water deprivation test
o If water deprivation results in dilute large volume of urine, then cause is likely not
dipsogenic (but central or nephrogenic)
• Desmopressin test (ADH analog)
o Central and Gestational respond to this treatment
o Nephrogenic does not
• If kidneys are insensitive, then they won’t respond.
49
Dr Elham Sharif
EXAMPLE 4 CONT’D

50. Hypernatremia
• Hypernatremia: Na level > 145 mEq/L.
• Causes:
• Water lost from vomiting or diarrhoea or excessive sweating (i.e. loss
of hypotonic fluid).
• or Na+ gain through acute ingestion or infusion of hypertonic solutions
containing sodium during dialysis.
• or diabetes insipidus, and when sodium is retained as through
acute ingestion.
• Conn’s syndrome: (primary hyperaldosteronism), results in
increased Na+ reabsorption and potassium excretion.
• Measurement of urine osmolality to evaluate the cause:
o In renal loss, urine osmolality is low or normal
o In extra-renal losses of water, the urine osmolality increased.
50

51. Evaluation of Hypernatremia
If plasma Na+ is > 145 mmol/L, measureurine osmolality
Urine osmolality< 300 mOsm/Kg
Diabetes insipidus DI (central or nephrogenic)
Urine osmolality 300-800mOsm/kg
Partial defect in ADH release (partial DI)
Diretics
Osmotic diuresis
Urine osmolality> 800 mOsm/Kg
Excess Na intake
Insensible water loss
GI loss of hypotonic fluid
Loss of thirst
Treatment must be gradual… coz rapid correction may
lead to cerebral oedema and death
51Dr Elham Sharif

52. What is renal hypertension? (renovascular hypertension)
BEFORE
AFTER
PLAQUES OR FIBROSIS
1) “ESSENTIAL” HYPERTENSION
-no specific cause
-body unable to regulate BP
-systolic BP >140, diastolic > 90mmHg
-managed with meds, diet, and fluid
regulation (ACE inhibitors/diuretics)
2) SECONDARY HYPERTENSION
-commonly due to renal artery stenosis
due to atherosclerosis.
-usually diagnosed after long-standing
HTN becomes unmanageable.
-results in very high BP-systolic >200,
diastolic >100 mmHg.
-RBF (sensed as a in BP) results 
RENIN, causing peripheral
vasoconstriction, Na/H2O retention
&  in BP.
52

53. Potassium K+
• Major IC cation, 20-fold> IC than EC
• Only 2% circulate in the plasma, with Na+ K+-ATPase pump
largely responsible for maintain the K+ gradient.
• Major physiologic functions:
o Neuromuscular excitation
o Regulation of cellular process
o Contraction of the heart muscle and cardiac rhythm
o Affecting acid base balance
• Regulation
o Extracellular balance is maintained by the kidneys
53Dr Elham Sharif

54. Clinical significance
Hypokalmeia
• Plasma K+ < 3.0 mEq/L
• Caused by: ↓ deitary intake
• Excess insulin causes ↑ cellular
uptake of K+
• Hyperaldosteronism, diuretics &
licorice ingestion causes renal
loss if K+
• Vomiting, diarrhoea & laxative
abuse… loss K+ from GIT
• Symptoms,
o Muscle weakness, paralysis,
cramps, tetany, polyuria
o In sever hypokalemia causes death
due to respiratory failure
Hyperkalemia
• Plasma K+ > 5 mEq/L
• ↑ dietary intake of K+
• ↑ cell lysis
• Acidosis & insulin deficiency…
altered cellular uptake.
• Drugs: e.g. Digoxin
• Renal failure &
hypoaldosteronism…impaired
renal excretion of K+
• Leukocytosis, thromobocytosis &
haemolysis… pseudohyperkalemia
• Symptoms:
o muscle weakness, abnormal cardiac
conduction… cardiac arrest.
dehydration
Normal Plasma Potassium: 3.5-5.0 mmol/L

55. Chloride Cl-
hypochloremia
• Cl- < 99 mEq/L
• Causes: prolonged vomiting loss of
HCL, Nasogastric suctioning ↑s
gastrointestinal losses.
• Diuretics & metabolic alkalosis ↑s
renal losses
• Burns ↑s loss of Cl-
• Minerolcorticoids excess
• pyelonephritis
hyperchloremia
• Cl-> 109 mEq/L
• Causes: GI loss diarrhea, loss of
bicarb & salicylate intoxication cause
RTA & metabolic acidosis.
• Dehydration.
• ↑ed sweat Cl- results (>35 mmol/L) in
diagnostic of cystic fibrosis.
• Cl- major EC anion of the body
•Referencerange: 99-109mEq/L(serum)
•Major functions: maintains of fluid balance& osmotic pressure.
•Cl- levels change proportionallywith Na+
55
Dr Elham Sharif

56. Bicarbonate
• 2nd largest anion fraction of the ECF
• It is the major component of the bicarbonate buffer
system in blood.
• Decreases result in metabolic acidosis.
• Increases in metabolic alkalosis
56Dr Elham Sharif

57. Bicarbonate (HCO3-)
• a. Second largest anion fraction of extracellular fluid
• b. Reference range: 22-29 mmol/L
• c. Clinically, the concentration of total carbon dioxide (ctCO2) is measured
because it is difficult to measure HCO3-.
• ctCO2 is comprised primarily of HCO3- along with smaller amounts of
H2CO3 (carbonic acid), carbamino- bound CO2, and dissolved CO2.
• HCO3- accounts for approximately 90% of measured ctCO2
• d. Bicarbonate is able to buffer excess H+, making bicarbonate an
important buffer system of blood.
• e. Clinical significance
• 1) Decreased ctCO2 associated with metabolic acidosis, diabetic
ketoacidosis, salicylate toxicity
• 2) Increased ctCO2 associated with metabolic alkalosis, emphysema,
severe vomiting.
update

58. Test procedures
sample collection and handeling
• Na & Cl-
o No special handling
o Serum or heparinised plasma
o Heparin anticoagulant
o Slight hemolysis has little effect coz RBCs has 10% Na and 50%
Cl.
o But sever hemolysis can lower Na by dilutional effect
• Bicarbonate
o Serum or plasma can loss CO2 gas if sample is exposed to the
atmosphere.
o If exposure prolonged the bicarbonate conc. will decrease by 3-4
mmol/l
o Sample handling and processing has minimal effect
58Dr Elham Sharif

59. • Potassium
o Sensitive to improper collection and handling of blood, may
result in false high level.
o Because the coagulation process releases K+ from platelets,
serum K+ maybe 0.1-0.5 mmol/L higher than plasma K+ conc.
• If the pts platelet count is elevated (thrombocytosis), serum
K+ maybe also elevated, avoid using heparinised specimen.
o if a tourniquet is left on the arm too long during blood collection,
cells may release potassium into plasma.
o Storing whole blood on ice promotes the release of K+ from
cells., thus whole blood for K+ determination must be stored at
RT and analyzed promptly or centrifuge to remove the cells.
o Hemolysis may give falsely high K+
Test procedures
sample collection and handling
59Dr Elham Sharif

60. Method of analysis
• Traditionally flame spectrometric method (atomic absorption & flame emission).
• Modern analyzer are based on electrochemical methods using ion-selective
electrode ISE.
• The heart of ISE is a membrane that contain ionophores having specific affinity
for the analyte ion.
• When blood contact these membranes, analyte ions from the blood (e.g. K+)
bind to one side of the membrane, creating a potential across the membrane.
• This potential is measured and used to calculate the concentration of K+ ions in
the blood.
• Sodium: Na electrode typically use glass (silicon dioxide, sodium oxide..etc)
membranes that has specific affinity to Na ions.
• Potassium: potassium selective membranes used antibiotic valinomycin
imbedded in plastic membrane.
• Chloride: ion-selective electrodes for Cl has a quaternary ammonium salt as
the ionophore, such as tri-n-octyl-propyl-ammomium chloride decanol.
60

61. Method of analysis
• Bicarbonate of total CO2:
o Use also ISE that respond to CO2
o Typically this is a pH electrode covered with a
silicone membrane, which is permeable to CO2
61Dr Elham Sharif

62. Anion gap
• Is a mathematical formula used to demonstrate the electro-neutrality of the fluids.
• Formula =
Anion gap (Ag2+) = Na+ - (Cl- + HCO3) = 7-16 mmol/L
Anion gap (Ag2+) = (Na+ + K+) – (Cl- + HCO3
-) = 10-20 mmol/L
• Increased anion gaps can be caused by;
• Uremia, lactic acidosis, ketoacidosis, ingestion of methanol, ethylene
glycol, salicylate
• Large doses of antibiotics or toxins
• Increased net protein charge.
• Decreased anion gaps can be caused;
o Paraproteins
o Hypoalbuminemia, hypophosphatemia
o dilution
o Increased in K+, Ca+, or Mg+
62

63. • Using the values of the illustration:
= (Na+ + K+) – (Cl- + HCO3
-)
= (142 + 4) - (103 + 27)
=146 - 130 =16 (range: 10-20)
• Alternative formula:
= Na+ - (Cl- + HCO3
=142 - (103 + 27) =12
(range: 7-16)
63

64. Calcium, Phosphorous, magnesium is
covered under parathyroid gland next
spring

65. VIDEOS
• http://www.youtube.com/watch?v=1fvHXMfojto
• http://www.youtube.com/watch?v=5WDKVqNW_VQ
Dr Elham Sharif 65

66. References
• Bishop., ML, Fody., E.P. Schoeff, LE , Clinical Chemistry:
Techniques, Principles, Correlations (Bishop, Clinical Chemistry)
ISBN: 978-0781790451, Publisher: Lippincott Williams &
Wilkins; Sixth Edition, 2010.
• Marshall, W.J., Bangert, S.K.; Clinical Chemistry 6th edition,
ISBN 0-7234-3328-3 -Publisher: Mosby, Release date: 2008.
• Christenson, R.H., Gregory, L.C., Johnson, L.J. (2001).
APPLETON & LANGES OUTLINE REVIEW CLINICAL CHEMISTRY,
ISBN 0070318476, Publisher: McGraw Hill Companies.
66Dr Elham Sharif