Why is there such a difference in lab results? Hospital drawn v’s finger prick.

[shambles]

I had a multitude of tests done at the same time but the calcium is showing completely different each time when it’s a finger prick test and although I know it’s correct calcium that is the important result, I am interested to find out why so different and in fact which one is correct?

Hospital drawn Jan 13

Calcium 2.442.20-2.60

Corrected calcium 2.372.20-2.60

Finger prick August 13

CALCIUM * 2.59 mmol/L 2.15 - 2.55

Corrected Calcium 2.52 mmol/L 2.15 - 2.55

Hospital Drawn September 13(this was part of RBC magnesium test)

Calcium 2.42 mmol/L 2.10 – 2.60

Finger Prick Jan 14

CALCIUM 2.50 mmol/L 2.15 - 2.55

Corrected Calcium 2.48 mmol/L 2.15 - 2.55

I have not taken any supplements since August 13. So why the difference in the results?

[Jackie]

Hi Different Labs vary as different assays. This is no problem so long as you always have the ranges.Why are you so worried about calcium, it is in range?It must not go over range, can be a sign of parathyroid or too much vit D.If the finger prick is a t a reliable Lab eg Blue Horizon, that is fine.if not so reliable, personally I would say no value in having it done. If there is a problem in other cases the GP should do it OK. Calcium does vary a lot, monthly tests for someone with major problems is considered best. Most people ,if in normal range a lot less. It is an electrolyte so can be important.

Best wishes,

Jackie

[shambles in reply to Jackie]

Hi Jackie thanks for the reply. I am concerned because the surgeon said after the I had my thyroid removed that they clipped the parathyroid due my thyroid being so swollen and to keep an eye on my calcium levels as they were low after the operation which I know is common. Right after the operation my eyes went off, TED and I was on IV steroids for 5 months before someone at the hospital highlighted my calcium was way too low and I should have been in supplements when on steroids. The GP gave me a pill to take at the surgery were you have to sit still for half an hour as sometimes it gets stuck! I'm ashamed to say I don't even know what it was. The endo then said there was probably bone damage because I hadn't been given calcium supplement so sent me for a bone density scan but that we all good. But I cannot for the life of me get my calcium levels right now. My GP is disinterested which is why I pay for tests. I was taking calcium supplements and and 1000 IU of vit D3 but when I tested in August my levels were pretty high so I stopped. My phosphate is over range as it was in August. So I wonder if I have over supplemented? My vit D is in range, just.

[Jackie in reply to shambles]

Hi I see.If you have the finger prick done via Blue Horizon, they use a phial of blood not a card, that is fine,It is only the corrected calcium that matters.What you described would be totally logical as with a serious PTH problem, then the calcium goes way over range.However, you should be well over that now.Calciu is Endo really.

The tablet would be for Alendronic acid for osteoporosis, bone scan , DEXA would have confirmed this was OK , why the GP stopped it. It is usual to have a follow up scan every 3 years but does not sound as if you ned it. That is ndo too.

If your D is low, it would be OK to take some vit D, probably with calcium but it must be prescribed, preferably by an Endo, very specialised.

I have terrible problems with Calcium and I honestly do not think you need to worry. Thyroid OPs etc do cause havoc for a while.

I hope that helps.

Jackie

[shambles in reply to Jackie]

Thanks Jackie, I am going to stop worrying I think Thanks for making sense of the unknown pill too.

[bantam12]

Finger prick tests are not as accurate, I had 2 vastly different VitD results, one taken at the GP and one finger prick both done at the same time.

As Jackie says calcium changes all the time, I have monthly calcium tests as I have hypercalcemia and the results are never the same. Personally I wouldn't bother with finger prick tests again as you can't rely on the result.

[shambles in reply to bantam12]

Hi hypohen thanks for the reply. You will understand calcium levels and I'm sorry you have hypercalcemia. I don't understand calcium levels but mine have been all over the place since I had my thyroid removed and given steroids for TED. As I explained to Jackie, I think I may have over supplemented as I have high phosphate which as I understand it means I should have low levels of calcium. I had it in my head that it would take a long time for calcium levels to alter, something like 3 months to see a notable change but I guess I'm wrong about that. Will fasting make any difference to the results and the two high readings were both fasting tests?

[bantam12 in reply to shambles]

The only high result I can see is the finger prick test at 2.59 but your corrected is 2.52 so in range and ok. Calcium level can change very quickly, although mine is high my Vit D is low so i should be taking VitD supps but they send my calcium even higher within a few days and when I stop them calcium goes down again within a few days.

You probably don't want to be taking calcium supps as you are top end of the range but it would be worth getting a Vit D test done to see whereabouts that is and maybe parathyroid as well. Taking high doses of Vit D can cause your phosphate to rise but here are other reasons.

By the way my VitD on a finger prick test came back at 77, the hospital test was 41 which is a big difference.

[shambles in reply to bantam12]

Thanks for putting my mind at ease and educating me :-). Just sent of my vit d test today, so I wonder what number I will get!