esp; thnx to my supervisor dr.Sahar iqbal (consultant chemical pathologist )

1. SERUM PHOSPHATE Dr.G.Murtaza
DIMC

2. INTRODUCTION
An adult has about 600g or Appro: 20mol of phosphorous
in organic& inorganic phosphate
85 % is in skeleton rest is principally in soft tissue
Phosphate is predominantly an intracellular anion
Phosphate plays an essential role in many biological functions such as
the formation of ATP, cyclic AMP, phosphorylation of protein &
in nucleic acid

3. BIOCHEMISTRY &
PHYSIOLOGY
Plasma contain both organic & inorganic phosphate but
only inorganic phosphate is measured
 Inorganic phosphate exists as both in monovalent
(H2PO4¯ ) & divalent(HPO4¯ ¯ ) phosphate ion
The ratio of monovalent & divalent is pH dependent ;
varies form 1;1 to 1:4 in acidosis & 1;9 to alkalosis
 10% of phosphate in serum is protein bound ,35 % is
complexed with sodium, calcium & magnesium & 55% is
free

5. REGULATION OF PHOSPHATE
 Regulation of phosphate is complex under control of
Kidney, intestine & skeleton
 throughout 24 hours Plasma Phosphate Concentration
shows Diurnal
variation with significant increase in Evening meal ,Peak
in early hours of morning & decrease to nadir in the
early morning
 This circadian rhythm is almost completely removed by
fasting

7. PARATHYROID EFFECT

8. FIBROBLAST GROWTH
FACTOR 23
FGF23
Inhibit 1-alpha hydroxylase
Increase fraction excretion via
kidney
Bone cells release ( osteoclast ,osteoblast )
Increased Sustained Plasma phosphate
Increased plasma 1,25 (OH)2D

10. CLINICAL SIGNIFICANCE
HYPOPHOSPHATEMIA
CONCENTRATION BELOW 2.5 MG/DL
MODERATE DEFICIENY : 1.5 -2.4GM/DL
shows no sign & symptoms
SEVERE DEFICIENCY : <1.5 MG/DL
shows sign & symptoms because phosphate is necessary for cellular function

11. Causes

13. HYPERPHOSPHATEMIA
 A plasma phosphate level higher than 4.5 mg/dL is
hyperphosphatemia
 the commonest cause of a high plasma phosphate is in vitro
seepage from red cells or hemolysis (factitious
hyperphosphatasemia);
 the commonest pathological etiology is renal failure ( dec GFR )
 Serum phosphate does not rise above normal until the glomerular
filtration rate falls below 30 ml/min per 1.73 m^2.

14. Causes

15. MEASUREMENT OF
PHOSPHATE

16. URINARY PHOSPHATE
EXCRETION
 best method for assessing renal tubular reabsorption
of phosphate
 Urinary phosphate excretion varies with age, muscle
mass ,renal function PTH ,time of day ,
 Urinary excretion of phosphate varies widely with diet
,& essentially equivalent to dietary intake
 24-hour urine specimens must be collected in an acid-
washed, detergent-free container. Acidify with HCl.( to
avoid Phosphate complex formation ) .

18. REFERENCE VALUES

19. Thank you ….

20. REFERENCES
A PRIMER OF CHEMICAL PATHOLOGY( Walmsley)
Tietz book of clinical chemistry chapter 64 edition 6th