Clinical Chemistry

Pt is euvolemic. [Na+] < 135 mmol/L – DDx?

– rapid correction =>?

– slow correction =>

SIADH ([Na]urine>20mol/L), drugs (1ADH-like)


– Cerebral edema

1desmopressin,SSRI, TCA, ecstasy

[Na+] < 135 mmol/L

Osmolarityserum > 280

Dx – causes?

Pseudohyponatremia <– hyperglycemia, hyperlipidemia, hyperproteinemia

Pt is hypovolemic

[Na+]serum < 135 mmol/L , [Na+]urine > 30mmol/L 


Hyponatremia-Renal losses

<– diuretics, medullary renal disease, Addison,RTA I

Pt is hypovolemic

[Na+]serum < 135 mmol/L , [Na+]urine < 30mmol/L 


Hyponatremia- Extrarenal loss

<– GI, 3rd spacing



Na+ administration <– IV, sodium bicarbonate, high-dose Na+ -Antibiotics

Dehydration <– DI, DM, diarrhea, sweating, osmotic diuretics

Pt: elevated [K+]serum, no in vitro hemolysis

no clinical evidence of hyperkalemia


Pseudohyperkalemia–> no Rx required

thrombocytosis/leukocytosis –> 1passive transm K+leak

familial –> 1RBC , autos. dom. chrom 16

Acidosis and hypokalemia



Increased Ca++, Cl, nephrogenous cAMP

decreased PO4-2   — Dx? Most common cause?

1o hyperparathyroidism

1.Adenoma(90%), 4-gland hyperplasia, carcinoma

Hypercalcemia, increased nephrogenous cAMP, nml PTH


Humoral hypercalcemia of malignancy–>PTHrP

RCC, SCC of lung/head&Neck/ skin/esophagus/cervix, breast ca, Islet cell tm, paraganglioma, TCL

clear cell ca (ovary)

Granulomatous disease and hypercalcemia



histiocytes of granulomas –>+ VitD–>1,25(OH)2VitD

Pruritus, “metastatic” calcification of vessel walls and soft tissue (GI/skin bx’s)


Calciphylaxis;–long term hypercalcemia a/w hyperphosphatemia

s/p renal transplant and hyperparathyroidism


Tertiary hyperparathyroidism

parathyroid –>autonomous => 1o hyperparathyroidism

Effect of acidosis and alkalosis on free Ca++

Acidosis–> increases free Ca++

Alkalosis–> decreases free Ca++

“Loses Calcium, Ads Calcium”

Which fraction of Calcium is biologically active => accurate reflection ofclinical Calcium status

free Ca++

50% –> protein bound (mainly albumin)

Sample for Ca++ measurement requirements

Arterial blood, no exposure to air / EDTA/Citrate

avoid fist clenching & prolonged tourniquet application

rapid delivery , keep cool

Correction of Ca++ for low protein

0.8mg/dL Ca++ per 1g/dL protein lost

Avoid if: Acid-base disturbances, neonates, renal insufficiency, liver disease

PTHrP secreted by which normal epithelia?

compare with PTH?

Sqaumous and lactating breast epithelium

PTHrP ~ N-terminal PTH –> biologic activity , short t1/2

–> can be specifically assayed

Low PTH/Calcium, Increased Phosphate,

Low 1,25(OH)2D levels



acquired–>most common

hereditary–> isolated / a/w DiGeorge syndrome

Low Calcium, PTH = nml-high

tissue deposition of calcium salts,brown tm’s of bone1


2o hyperparathyroidism (pseudohypoparathyroidism)

<–peripheral resistance to PTH –>+ osteoclasts1

Chronic renal failure, VitD deficiency

Magnesium and PTH secretion

– mild transient decrease of Mg++

– persistent/ marked decrease of Mg++

– increased PTH–>balance of divalent cations

– inhibition of PTH secretion

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