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. 2019 Apr;11(8):689-701.
doi: 10.4155/bio-2018-0295. Epub 2019 Apr 17.

Feasibility of measuring sodium, potassium and creatinine from urine sample on dried filter paper

Mohamad Tarik  1 , Lakshmy Ramakrishnan  1 , Ritvik Amarchand  2 , Harshal Ramesh Salve  2 , Prashant Mathur  3 , Pradeep Joshi  4 , Anand Krishnan  2
Affiliations

Feasibility of measuring sodium, potassium and creatinine from urine sample on dried filter paper

Mohamad Tarik et al. Bioanalysis. 2019 Apr.

Abstract

Aim: To develop a bioassay for estimation of sodium, potassium and creatinine in dried urine strips and comparing with their respective concentration in liquid urine samples. Materials & methods: Urine was collected on filter paper strips, dried at room temperature and, eluted for estimation of sodium, potassium by indirect ion selective electrode method and creatinine by Jaffé method. Result: This bioassay was validated based on the US FDA guidelines for bioanalytical method validation and was linear, sensitive, accurate and precise with acceptable recovery and matrix effects. Analytes were stable in dried urine strips during 1 year of storage at 4°C. Conclusion: We conclude that the dried urine is suitable for analysis of sodium, potassium and creatinine and offers a convenient alternative for monitoring dietary salt intake.

Keywords: cardiovascular disease; dried urine strip; electrolytes; hypertension; kidney dysfunction; salt intake.

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Conflict of interest statement

Financial & competing interests disclosure

Authors thank the Indian Council of Medical Research and WHO for providing financial support for National NCDs Monitoring Survey from which this pilot study was carried out. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript apart from those disclosed.

No writing assistance was utilized in the production of this manuscript.

Figures

Figure 1.
Figure 1.. Diagrammatic representation of dried urine strip bioassay.
DUS: Dried urine strip.
Figure 2.
Figure 2.. Comparison between dried and liquid urinary sodium, potassium and creatinine analysis in 134 samples: linear correlation and Bland–Altman agreement.
For urinary sodium: (A) linear regression plots; solid line represents the data best fit (R2 = 0.888); and (B) Bland–Altman plot for agreement analysis of dried urine and liquid urine sample. The bias was -5.27 and LoA ranged from -47.56 to 36.99 mmol/l. For urinary potassium: (C) linear regression plots; solid line represents the data best fit (R2 = 0.906); and (D) Bland–Altman plot for agreement analysis of dried urine and liquid urine sample. The bias was 1.36 mmol/l and LoA ranged from -5.08 to 7.78 mmol/l. For urinary creatinine: (E) linear regression plots; solid line represents the data best fit (R2 = 0.909); and (F) Bland–Altman plot for agreement analysis of dried urine and liquid urine sample. The bias was 2.65 mg/dl and LoA ranged from -10.35 to 15.65 mg/dl. SD: Standard deviation.
Figure 3.
Figure 3.. Storage stability of sodium, potassium and creatinine in dried urine after 1 year at 4°C and comparison with baseline analysis in dried and liquid urine in 134 samples.
For urinary sodium: (A) and (B) Bland–Altman plot for agreement analysis of 1 year dried and liquid urine sample. The mean difference was -3.93 (2SD limits: -42.52–34.66) mmol/l and 1.23 (limits: -24.86 to 27.27) mmol/l in dried urinary sodium after 1 year when compare with baseline sodium levels in liquid and dried urine, respectively. For urinary potassium: (C) and (D) Bland–Altman plot for agreement analysis between 1 year and baseline potassium in liquid as well as dried urine, respectively (meam difference was -0.839 mmol/l [LoA: -11.53–9.86] and -0.374 mmol/l [LoA: -13.51–6.03]). For urinary creatinine: (E) and (F) Bland–Altman plot for agreement analysis The difference was -6.6 mg/dl (LoA: -32.78–19.58) and -11.25 mg/dl (LoA: -34.47–11.97) mg/dl with baseline dried urine and liquid urine sample. SD: Standard deviation.
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