A 58 year old man, seeing his Family Doctor. Clinical information is
'Swollen foot, ?gout'. A serum sample taken at 11.30am gave the following
results:
Sodium: 138 mmol/L
Potassium: 4.5 mmol/L
Urea: 6.4 mmol/L (2.8 - 7.0)
Creatinine: 112 umol/L (62 - 133)
Adjusted calcium: 2.41 mmol/L (2.10 - 2.55)
Phosphate: 0.59 mmol/L (0.81 - 1.55)
Uric acid: 489 umol/L (male, 208 - 506)
This Case, which we thought would be straightforward, attracted a wide
range of opinion and action, and a total of 31 participants. Just for once,
no-one suggested telephoning the Family Doctor (and no-one suggested adding
thyroid function tests!).
17 thought that the urate which was within reference limits did not exclude
classical gout; [2.0]
2 queried osteoarthritis/ osteomalacia; [0.7]
1 queried another cause for the swollen foot such as playing football with
grandchildren; [*0.5]
1 queried pseudo-gout; [-0.3, one assessor pointing out that this typically
affects the knee joints of elderly females]
1 thought that the urate excluded classical gout. [-1.7]
9 suggested that crystal microscopy of joint fluid was needed to confirm
diagnosis; [0.3]
1 said that diagnosis of gout cannot be made from serum tests. [1.0]
7 queried alcohol as a cause of the low phosphate (and also gout); [0.7]
4 said that a low phosphate was consistent with acute gout; [0.7]
3 queried whether the low phosphate was caused by a previous carbohydrate
load; [*0.3]
2 queried drug-induced gout; [0]
1 each queried
hyperparathyroidism; [-1.3]
a malnourished diabetic taking antacids; [-1.0]
diuretic use [0]
a tumour [*0]
congenital hypophosphataemia. [-1.3]
A bewildering array of other tests and action was suggested.
6 would measure gamma-GT; [0.7]
6 would suggest a repeat phosphate, preferably fasting; [1.3]
4 would measure CRP and/or ESR; [1.3]
3 would measure glucose; [0.7]
2 each would measure
LFTs [0.7]
Lipids [-0.3]
alkaline phosphatase; [0.7]
MCV; [0.7]
magnesium [0].
2 would suggest an X-ray; [1.3]
1 each would measure
24-hour urinary uric acid; [0]
total protein and albumin; [0]
immunoglobulins and protein electrophoresis; [0]
Creatine kinase; [-0.7]
paracetamol; [-1.0]
urine microalbumin and phosphate; [-0.3]
PTH and 1, 25 OH Vitamin D; [-0.7]
amino acids. [-1.0]
1 would suggest referral to a Rheumatologist; [0.3]
1 suggested a therapeutic trial of a non-steroidal anti-inflammatory drug.
[0.7]
This report originally left this Department without comment (tut, tut) and
I was 'phoned about it by the Family Doctor a couple of days later. He knew
that a normal urate did not necessarily exclude gout, but was puzzled by
the low phosphate and wondered whether this could suggest pseudo-gout. The
sample wasn't post-prandial. I didn't know the answer, but turned to my
stand-by for awkward questions, Tietz's admirable 'Clinical Guide to
Laboratory Tests'. I found that this lists acute gout as one of the causes
of a low phosphate (presumably through co-deposition of phosphates in the
affected joint)- I didn't know that. I am relieved to see that neither did
most of the participants and the assessors! So my advice was simply
'Consistent with acute gout'
Best wishes
Gordon Challand
Ping Li
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