PTH, Minerals, Vit D Flashcards by Sarah Carlson

Pt has c/o mild fatigue and an elevated serum Ca of 11.5. What is the most likely cause of this patient’s hypercalcemia? Would you order any other lab tests?

Hyperparathyrdoidism?

PTH
PO4

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A PTH of 165 is?

HIGH!

normal 15-75

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A PO4 of 2.8 is?

low

normal 2.5-4.5

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What is the MCC of hypercalcemia in an outpatient setting?

primary hyperparathyroidism

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What are the top three causes of primary elevation of PTH?

– 85% benign parathyroid neoplasm or adenoma – 10% parathyroid hyperplasia (3% MEN)
– 2% parathyroid carcinoma

**Usually doesn’t cause serum Ca >12 mg

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What percentage of patient’s with primary hyperparathyroidism have bones, stones, groans and moans?

<20%! Most people are asymptomatic

Usually in F in pts >45 yrs, otherwise similar sex diffs

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In addition to PTH and PO4 what other lab tests hsould you order?

urine Ca (24 hr preferred)

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How do you evaluate hypercalcemia?

Total Ca >10.5 or ionized Ca >5.6 
>
causative diseases vs meds
>
measure intact PTH level
>
normal/high
>
24 hr urine Ca level

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If 24 hr urine Ca is low….

familial hypocalciuric hypercalcemia

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If 24 hr urine Ca is normal/high…

primary/tertiary hyperparathyroidism

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Describe Ca equilibria in blood

High pH: Ca is bound to PROTEIN (albumin, globulins) 40-45%

Lower pH: Free (ionized)

Complexed: PO4, HCO3, Lactate (5-10%)

*All are pH dependent

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What happens to free Ca in alkalemia?

HIGHER pH –> free Ca decreases, increase in Pr-bound Ca

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What happens to free Ca in acidemia?

LOWER pH –> free Ca increases, Pr-bound Ca decreases

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For each .1 change in pH, free Ca changes by ….

Does total Ca change?

NO!

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What is the major clinical utility of ionized Ca?

Ensure maintenance of hemodyanmic fxn
monitor pts in critical care
- higher mortality in septi pts with hypocalcemia
- neonates
- pts w/ pancreatitis/renal disease
diagnose/treat hypercalcemic/hypocalcemic conditions

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What reflects TRUE Ca status, is unaffected by protein concentration and requies stringent collection/handling because its pH sensitive?

Free (ionized Ca)

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What reflects (free + protein-bound + anion bound), depends on protein concentration and is not affected by pH?

Total Ca

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What formula is often use to correct Ca to account for protein?

Corrected Ca (mg/dL) = Measured Total Ca (mg/dL) + 0.8*[4-Albumin (g/dL)]
• Correction fails to accurately predict calcium status in individual patients

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How do you correct iCa for pH changes?

Corrected iCa = Measured iCa [1-0.53(7.4-measured pH)]

Limited range of correction (pH 7.2-7.6)
Assumptions: patient has pH of 7.4, no variation in albumin, no additional iCa binding proteins or anions
Preferable to avoid pre-analytical issues entirely

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When should iCa be tested?

total Ca is <8 or >10.2

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How can parathyroidectomies be guided by serum PTH concentrations?

• Decrease in PTH of > 50% 10 minutes post-resection signals success in removing the abnormally secreting parathyroid tissue
• Rapid turnaround time is essential
– Shorter incubation
– Compromised sensitivity

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47 year old female
• 5’4, 140 lbs
• BP: 110/90
• 2-week history of fatigue and midback pain (6 out of 10)
• Described pain as aching, worse in the morning and aggravated by movement
• Laboratory tests unremarkable except for serum total calcium of 16.7 mg/dL

+ Family hx for cancer

What is the most likely cause of this pts hypercalcemia?

occult malignancy

What is the MCC of hypercalcemia in the outpatient setting when Ca < 12

hyperparathyroidism

What causes hypercalcemia by increasing synthesis of 1,25-(OH)2 vitamin D from macrophages within the granuloma?

Sarcoidosis

macrophages in the granuloma increase synthesis of vit D

What vitamin intoxication can increase Ca to 12-14 mg/dL?

vit A (50,000 to 100,000 IU)

What lab tests would you order to confirm the diagnosis of an occult malignancy causing hypercalcemia?

iPTH was 20... Suppressed Do a sxs guided malignancy work up

What are labs to test for solid tumors?

increased PTHrP: adeno and sq cancer (lung tumor) Increased alk phosphatase: bone lysis (breast tumor)

What are labs for hematologic malignancies?

+ myeloma screen: MM | increased calcitriol: lymphoma, granulomatous disease

What is PTHrP?

it is DISTINCT from PTH but has some N terminal homoogy so can interact with the PTH receptor and mimic PTH activity

What is the normal range for PTHrP?

1-2 pmol/L | collect and process on ice with protease inhibitors!

71 year old female referred to endocrinology clinic after several years of unresolved hypomagnesemia (NORMAL 1.7-2.5) • Numerous hospital admissions to receive IV magnesium • Previously presented with palpatations (x3) and once with diarrhea and vomiting • Medical history included type 2 diabetes mellitus and hiatal hernia • Medications: simvastatin, esomeprazole/Nexium, verapamil, pioglitazone, metformin • Supplementation: calcium, magnesium, vitamin D • Clinical examination unremarkable • Normal ECG and echocardiogram MG .52 CA 6.84 WHAT COULD BE THE CAUSE OF THIS PT'S HYPOMAGNESEMIA?

``` • Renal – Medication (diuretics, cisplatin, aminoglycosides, cyclosporine) – Infection (pyelonephritis, glomerulonephritis) – Osmotic diuresis • Gastrointestinal – Diarrhea, vomiting – Laxative abuse – Lack of intake or absorption of dietary Mg – Malabsorption – Malnutrition – Alcoholism – TPN • Leads to secondary hypoparathyroidism ```

What is PPIH?

PPI induced hypomagnesemia * Median # of years before onset: 5.5 years * Mechanism largely unknown * Clinical guidelines recommend obtaining serum Mg on new patients starting PPIs and regular monitoring of patients on long-term PPI therapy * Relatively rare complication * Patients at greater risk: GI disorders, diuretics

12 mo M presents for pediatric WCC - breastfed since birth - meeting mile stones - mild vaglus varus both legs * CBC:normal * iPTH:334pg/mL * Phosphorus:2.5mg/dL • Magnesium: 2.3 mg/dL • Totalcalcium:9.7mg/dL What is the most likely cause of this child’s elevated PTH?

Vit D def

If you suspect vit D def in a child what other tests would you order?

25-hydroxyvitamin D

What is required to convert 25 OH vit D to 1,25 OH vit D?

PTH!

D3 vs D2: syntehsized in the body

D3 (D2 plant)

D3 vs D2: synthetically derived supplement

D2 (D3 natural)

Leads to a sigfniciant increase in total 25OH vit D in body

D3 (D2 only moderate)

What form of vit D is recommended by experts for optimal bone and immune support?

What lab is the best indication of a patient's true vitamin D status?

25-OH (t1/2 2-3 weeks)

How does vit D prevent hypocalcemia?

it inhibits PTH

What biochemical changes are assocaited with vit D deficiency?

Decrease in 25OHD Decrease urCa INCREASE in PTH Eventual decrase in Ca/Phos

What is Rickets?

* Originated in late 1600’s * By 1900 > 80% children in industrialized cities in North America and Europe suffered from rickets * 1920’s: irradiation/fortification of milk became common practice; eventually saw eradication of rickets * C-sections increased; rate has remained the same since after WWII

What are signs of Rickets?

* Skeletal deformities (delayed fontanelle closure, bowed legs, breastbone projection) * Weakness * Unable to stand or walk * Slow growth * Bone pain and tenderness * Seizures * Dental deformities

Where is Rickets becoming more common now?

(children): prevalent among immigrants from Asia, Africa, and Middle Eastern countries • Vitamin D deficiency associated with Fe deficiency; treatment with Fe can increase 25(OH)D concentrations • More likely to follow dress restrictions limiting sun exposure • Darker pigmented skin converts UV rays to vitamin D less efficiently than lighter skin

What sort of supplementation is required for every age?

– Birth – 1y: 400 IU – 1-70y: 600 IU – 71+ y: 800 IU – Breastfed infants need supplementation!

How much vit D shoiuld you get during pregnancy?

* Current requirement: 600 IU * Supplementation with 800-1600 IU/day * Supplement with vitamin D3 or D2? D3 is what is quantitatively transferred in human milk

How much vit D supplementation is recommended for neonates?

400 IU | Breast milk is DEFICIENT in vit D

How much vitamin D should lactating women receive?

400 IU/day

What can be used for 25OH vit D screening?

immunoassays

What is the most accurate test used to test for vit D def and who should it be used for?

LC-MS/MS CKD pts pediatrics pts on vitamin D supplementation

Where is the greatest prevalence of vit D def?

Inpatients/hospitalized adults

What indicates a vit D def?

<20 (20-60 ref range)

What vit D levels are considered toxic?

>150