Reference Interval of Spot Urinary Oxalate to Creatinine Ratio in Children
Condition: Hyperoxaluria
Study type: Observational

Summary: 
      Reference intervals (RI) of oxalate for the Pakistani population are not readily available.
      The values used by most labs are usually taken from the literature from studies mainly
      performed on Caucasian or from the manufacturer package insert of oxalate reagent kits [2].
      RI of an analyte assist the clinician in differentiating between health and disease [3]. It
      is established by testing healthy populations and figuring out what appears to be "normal"
      for them after defining the reference population demographically. Careful determination and
      verification or validation of RI by the laboratory are essential to ensure proper utility.
    

Detailed description: 
      A cross-sectional study was conducted at Section of Chemical Pathology, Department of
      Pathology and Laboratory Medicine, Aga Khan University, Karachi, from June 2018 to October
      2019 after approval from Aga Khan University Hospital's ethical review committee.

      Inclusion criteria included children less than six years of age, not suffering from any
      illness during the last two weeks and no hospitalization since the last four weeks. Children
      on vitamins or history of kidney stones or family history of kidney stones were excluded.

      A standardized questionnaire was used, and recommended target sample size was calculated
      using CLSI Guidelines C28-A3. Non-probability (consecutive sampling) was done. Parents or
      guardians of each reference individual were invited to participate in the study. An
      explanation of the study, consent form (written in the local language, in accordance with the
      guidelines of the local ethics committee), and the procedure for participation were explained
      to the parents by the primary investigator. Those who consented were provided with a
      container for urine collection, and the procedure for the collection was explained. A 5ml
      random morning urine sample was collected and stored at -30 ºC until analysis after adding 6M
      hydrochloric acid.

      Urinary Oxalate was measured on Micro lab 300 using a kit based on the oxalate oxidase
      principle by Trinity Biotech Plc, Wicklow, Ireland while creatinine was measured by kinetic
      Jaffe reaction ADVIA 1800 by Siemens Diagnostic, USA. Samples were analyzed in batches with
      quality control specimen for validating the results. Oxalate to creatinine ratio (Ox: Cr) was
      calculated. College of American Pathologist, USA accredits clinical Laboratory of Aga Khan
      University Hospital.

      Data were analyzed by EP evaluator and SPSS 23. Subjects were categorized based on ages into
      five groups. Group I (0-6 months), Group II (6 months-1 years), Group III (1-2 years), Group
      IV (2-4 years), and Group V (4-6 years). Descriptive data were analyzed for frequencies and
      median with IQR. P-value <0.05 was taken as statistically significant.
    

Observational model: Cohort
Time perspective: Cross-Sectional
Sampling method: Non-Probability Sample
Study population: 
        Healthy children less than 6 years of age (both genders)
      
Keywords: Spot oxalate to creatinine ratio; Reference intervals