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Hi Marieke,
Low urinary sodium in association with hyponatraemia is usually due to maximal activation of the RAAS and can be due to: extrarenal salt loss (from GIT or sweat) but patient would be usually hypovolaemic; reduced effective circulating blood volume as in cirrhosis & cardiac faliure but this should be clinically evident; or low inatke of dietary sodium. Acute water intioxication can also lead to low urinary sodium but associated with a low urinary osmolality. Your patient doesn't seem to fit any of these categories, it may be due to a combination of low dietary sodium (from reduced appetite) and activation of RAAS by the diuretic.
regards
Mohammad
Does anyone have thoughts on why this patient’s urinary sodium level would be low?
76 year old man with widespread lymphoma
Serum sodium levels have been low-normal for several months, but went down to 117 mmol/L on 16/7. The next day it was 121, with serum osmolality 259, urine osmolality 495, but urine sodium <20.
The last previous serum sodium was measured on 30/6, when it was 128.
He’d had 2U blood on 19/6, Fludarabine for the first time on 20/6 and only returned to the clinicians on 30/6 (day 10) despite having had a temperature of 37.9 one evening.
He was next seen on 16/7, when the sodium of 117 was measured, reporting that the fludarabine had been “hard going”. He’d had abdominal discomfort, a reduced appetite, some nausea, but no vomiting and regular bowels.
On 17/7 a second course of Fludarabine was started and 2U blood were given.
The follow-up serum sodium on 25/07 was 125, but the urine sodium was still <20.
|
Date |
Hb |
S-Na |
S-K |
S-urea |
S-creat |
S-alb |
S-osmo |
U-Na |
U-osmo
|
|
18/6/08 |
9.5 |
132 |
3.7 |
6.3 |
94 |
27 |
|
|
|
|
30/6/08 |
10.2 |
128 |
3.7 |
4.6 |
95 |
25 |
|
|
|
|
16/7/08 |
8.7 |
117 |
4.3 |
3.4 |
93 |
27 |
|
|
|
|
17/7/08 |
|
121 |
4.3 |
3.6 |
93 |
|
259 |
<20 |
495 |
|
25/7/08 |
10.2 |
125 |
3.9 |
5.7 |
101 |
27 |
268 |
<20 |
543 |
His other medications are Frusemide 40 mg od, Lanzoprazole 15 mg od, Allopurinol 300 mg od, Plavix 75 mg od (Clopidogrel) and Co trimoxazole.
He weighs 57 kg. PMH Hypertension and quadruple cardiac bypass in 1997.
The most likely explanations for the hyponatraemia would each be expected to result in a urine Na >20, and the urea and creatinine levels are not consistent with either true or “effective” volume depletion.
Any ideas gratefully received.
Thanks
Marieke
Dr Marieke Jordaan
Consultant Chemical Pathologist
Mid-Yorkshire Trust
Pinderfields General Hospital: (01924) 317060 or 08448118110 ext 57060
Pontefract General Infirmary: (01977) 606238 or 606681