Biochemistry

ELECTROLYTES PROFILES:

4 Major electrlytes (Na+,K+,HCO3-,Cl- ) and determination of body fluid conc. of those electrolytes are grouped
under a familial test of Elec. profiles.

Functions of Elec. :-
1. Body water homeostasis
2. Acid-Base balance
3. Regulation of muscle function (cardiac,smooth,skeletal)
4. Ruling electron transfer reaction
5.Co-factor for enzymes.


Fractional Excretion of Electrolytes:

(MEANING TUBULAR EXCRETION IS <1%)
An electrolyte conc. in urine is a useul indicator of renal handling of water and elec.

While GFR is considered as the best overall indicator of renal function, fractional excretion (FE) tests have been also proposed, especially for assessment of tubular function.
In renal physiology, FE of electrolytes is defined as the fraction of filtered electrolytes which escapes reabsorption and consequently is excreted in urine.
FE of an electrilyte (X) is calculatd using a random urine sample with simultaneously obtained serum sample for x and Cr.
So, FE x = (Urine X/Plasma X) * (Pls. Cr./Urn. Cr.) * 100 [xpressed as %]

Clinically Na+ is the most measured to distinguished renal from non-renal (pre-renal) causes of decreasedNa. So, for Na…

FE Na (%) =(Urn. Na. / Plasma Na.) * (Pls. Cr. /urn. Cr.) *100
Interpretation FE Na. :
No reference interval has been established
Elevation of FE for Na has been suggested as a means to differentiate azotemia due to intrinsic renal disease from that due to prerenal factors.
Another indication of FE test is Fanconi’s syndrome. Abnormal FE values however may be found in normal renal function (eg in primary hyperparathyroidism). A large number of factors (e.g. creatinine assay, age, diet, drugs) may moreover induce misinterpretation of FE.

In most normal subjects, the fractional excretion of sodium is usually less than 1 percent but may be raised with an increase in salt intake.
In acutely azotemic patients, a low fractional excretion of sodium ( <1%) usually indicates a prerenal process that is responsive to volume repletion. That is avid Na. Retention to compensate for xtr-renal fluid losses (vomiting, diarhoea, sewting or 3rd space losslike ascites).
A fractional excretion >1% in acutely azotemic patients usually indicates intrinsic renal injury,
(but is consistent with volume depletion in patients receiving diuretics,mineralocorticoid defeciency or in some patients with salt-losting nephropathy or chronic renal insufficiency)

Osmolarity /Osmolality:

Osmole: particle present in a soln. E.g. Na in plasma.
Osmolality: Osmoles per Kg of water.
Osmolarity: Osmoles per Liter of soln.
I n body fluids 2 measurement are so closed that they can used interchangeably.


Normal Osmolality:
280—295 mmol/L
Calculation =
2*Na. (mmol/L) +Glucose (mmol/L) + Urea (mmol/L).
So, if glucose and urea are normal then only 2*Na. Will do.

Osmoler Gap:
Disparity btn measuered osmolality (in Lab by an OSMOMTER) and the calculated osmolality.

Osm. Gap. =
Measured osmolality – Calculated osmolality.

Why not calculated minus measured?
Other osmotical substances increases the measured without altering Serum Na and therefore ,
Measured >Calculated osmolality.