Article Type : Research Article
Authors : Kowsalya R
Keywords : Chronic Kidney Disease; Vitamin B12; Anaemia
Introduction:
Anaemia, followed by development of left ventricular hypertrophy then
cardiovascular failure, is the major cause of mortality in Chronic Kidney
Disease (CKD) patients. B12 deficiency is one of the major contributors to
anaemia in CKD. Nutritional deficiency due to dietary restrictions, deranged
metabolism of vitamins and loss of vitamins in the dialysis procedure are important
causes of vitamin b12 deficiency in CKD patients. Hence study of b12 deficiency
and its active form in CKD is essential.
Aim:
The aim of this is to assess performance of active vit B12 in comparison to
total vit B12 for the correct diagnosis of true vitamin B12 status in CKD
patients.
Study
Design: An observational cross sectional study
Place
and Duration of Study: Dept. of Biochemistry, Institute of Nephro-Urology,
Bangalore, India from July 2022 to December 2022
Methodology:
Study population consists of CKD patients attending Nephrology outpatient for
follow up. They were categorized into 5
stages using eGFR values. Laboratory tests including. Total vit B12 and Active
B12also known as Holo-Transcobalamin (Holo-TC) were assayed in all the
participants using Abbott chemistry analyzer.
Results:
In our study, a statistically significant (P value = <0.0001) vitamin b12
deficiency was observed in severe stages of CKD (stage 4 &5) than in
earlier stages (stage1, 2, &3). Holo TC had better sensivity, specificity,
positive predictive value and negative predictive value in predicting vitamin
b12 deficincy in CKD patients than total vitamin b12.
Conclusion:
Holo TC is the better indicator of vitamin B12 deficiency in CKD patients in
comparison with total vitamin b12.
A significant proportion of Chronic Kidney Disease
(CKD) patients have physiological vitamin B12 deficiency. CKD patients are at
higher risk of nutritional deficiency due to dietary restrictions, and
malnutrition. Deranged metabolism in CKD patients leading to metabolic
alterations and hormonal dysregulations is another contributor to vitamin b12
deficiency. Also dialysis procedure itself can cause loss of vitamins leading
to vitamin b12 and folic acid deficiency [1]. It’s well known that vitamin B12
along with folic acid is essential for the homocysteine metabolism in the body.
Hyperhomocystinemia, an immediate complication of vitamin B12 deficiency has
grown as an important risk factor for cardiovascular disease in CKD patients
[2]. Hence detecting vitamin B12 deficiency in CKD patients at the earliest is
more important as administration of intravenous B-Complex vitamins is proven to
be efficient in reducing serum homocysteine levels in CKD patients [3]. Vitamin
B12 in the blood is basically protein-bound and approximately 20% of
circulating B12 is bound to transcobalam in which is the biologically active
form that can be taken up into cells. That active form of vitamin b12 is also
called Holo-transcobalamin (Holo TC). CKD patients have an impaired tissue uptake
of vitamin B12 because of increased transcobalamin losses in the urine and
reduced absorption in the proximal tubule leading to a functional B12
deficiency which goes undetected by measuring only the Total b12 levels in CKD
patients [4]. Thus it is very important to measure Active vitamin B12 (Holo TC)
instead of total B12 levels in CKD patients. Also studies in this aspect in
general population, have shown that Holo TC would be a better indicator of
vitamin B12 status than total serum cobalamin, and may more accurately reflect
functional B12 status.5,8. The aim of present study is to assess performance of
Active vitamin B12 in comparison to Total vitamin B12 for the diagnosis of true
VitB12 status in CKD patients of different stages.
This was a retrospective cross-sectional study conducted in the Institute of Nephrourology, Bangalore, a tertiary care Centre for Nephro and urology care. Data was collected from the medical records and laboratory records of patients over a period of six months from July 2022 to Dec 2022.
Inclusion criteria
Adult patients both men and women of age group 20 to 60 year, diagnosed with CKD, attending routine nephrology outpatient department for follow-up were randomly selected and enrolled for the study.
Exclusion criteria
CKD patients, on vitamin b12 supplementation were excluded from the study. Cases were categorized into 5 groups CKD stage 1, to stage 5 as per KDOQI guidelines [5], using eGFR (estimated glomerular filtration rate) values. Different stages of CKD and their eGFR values included stage 1(eGFR >90), stage 2 (eGFR?60-90), stage 3 (eGFR 30-?60), stage 4 (eGFR?15-30), and stage 5 (eGFR?<15).Laboratory tests mainly Urea, creatinine, total vitamin B12 and active b12 (Holo TC) were done in all the patients enrolled in the study. eGFR was calculated by the CKD Epidemiology Collaboration (CKD-EPI) equation [6].
Sample Collection and lab Analysis
Blood sample was collected randomly by standard
venepuncture technique into plain plastic tubes using aseptic precautions.
Complete clot formation was ensured prior to centrifugation. Serum was
separated after centrifuging for 15 minutes, and was analysed for all the
parameters on the same day. Analysis of serum was done by Abbott ci4100
chemistry and immunoassay auto analyser in biochemistry laboratory. Ready to
use kits from Abbott architect ci systems were used for the analyses. Urea by
colorimetric method using urease method and creatinine using alkaline picrate
method. Vitamin b12 was assayed by Chemiluminescent Micro particle Immunoassay
(CMIA) method with reportable range of 148 pg/ml to 2000 pg/ml. Active vitamin
b12 (Holo TC) was assayed based on Micro particle Enzyme Immunoassay (MEIA)
technology with reportable range of 19 pg/ml to 128 pg/ml.
Statistical Analysis
Data were analysed by Statistical Package for Social Science (SPSS) version 17. Results were presented as mean ± Standard Deviation (SD) for quantitative variables. The significance level, or p-value, was calculated using the unpaired t-test. A P value <0.005 was considered significant. Sensitivity, specificity, positive predictive value and negative predictive value for the tests were calculated using formulas.
Results
A total of 103 patients with CKD were enrolled into the study as per the inclusion criterion. Patients were categorized into 5 stages of CKD using eGFR values as per KDOQI guidelines, mentioned above. Total vitamin B12 and Holo TC were analysed in all the patients. Biochemical data of the patients enrolled in the study are listed in Table 1. Among 103 CKD patients (n=103), 29 patients (29%) were in stage 5, 23 patients (23%) were in stage 4, 19 patients (19%) were in stage 3, 16 patients ( 16%) were in stage 2 and 1 of CKD. Both vitamin 12 and Holo TC values were lower in stage 5 CKD patients followed by stage 4, 3, 2 and 1 (Table 1).
Vitamin B12 Deficiency
Out of 103 CKD patients, around 36 patients (37%) had total vitamin B12 deficiency and 52 patients (53%) had Active B12 (Holo Tc) deficiency. On clinical examination, only 26% (n= 25) had symptoms of B12 deficiency like tingling and numbness, burning feet, particularly at night time
Effect of dialysis onB12 deficiency
Total Vitamin B12 and Holo TC were predominantly lower in CKD patients on dialysis for more than five years duration compared to those on dialysis for less than five years which was significant with p value (<0.0001) at 95% confidence interval (Table 2) (Figure 1).
Total Vitamin B12 vs Holo TC
From the methodology of both Total b12 and Holo TC the upper cut off and the lower cut offs were defined. (Table 3). Seven patients had lower cut off value (<148) for total vitamin B12 and twelve had lower cut off for (<19) for Holo TC. None had higher cut off (>2000) for vitamin B12 and six had higher cut off for HoloTC. Based on these results and also on the clinical features of B12 deficiency in CKD patients, sensitivity, specificity of the tests were calculated for vitamin B12 and Holo TC. Holo TC showed high sensitivity and specificity compared to vitamin b12 which was significant with p value of <0.005. Also positive and negative predictive values were higher for Holo TC than Total vitamin B12 (Table 4).
Figure 1: Effect of dialysis on vit B12 & HoloTC.
Table 1: Biochemical data.
Parameters |
Stage 1 CKD (?eGFR?<15) n=16 Mean ± sd |
Stage 2 CKD (?eGFR?15-30) n=16 Mean ± sd |
Stage3 CKD (?eGFR30-?60) n=19 Mean ± sd |
Stage 4 CKD (?eGFR?60-90), n=23 Mean ± sd |
Stag 5 CKD (eGFR?,>90) n=29 Mean ± sd
|
Age(yrs) |
51 ± 13 |
42 ± 11 |
41 ± 12 |
39 ± 14 |
37 ± 18
|
Urea (10-44mg/dl) |
35 ± 8 |
42 ± 7.1 |
79 ± 26 |
125 ± 35 |
158 ± 60 |
Creatinine (0.57-1.1mg/dl) |
0.8 ± 0.2 |
1.6 ± 0.1 |
2.2 ± 0.2 |
4.3 ± 0.2 |
12 ± 4.2 |
Vit B12 (191-663 pg/ml) |
688 ± 55 |
539 ± 137 |
390 ± 133 |
165 ± 55 |
140 ± 68 |
Holo Tc (35-128pg/ml) |
120 ± 12 |
98 ± 14 |
66 ± 15 |
33 ± 15 |
21 ± 6 |
Holo TC- Holo Transcobalamin, vit B12- total vitamin
B12 , CKD- chronic kidney disease |
Table 2: Comparison of total vitamin B12 and Holo Tc with duration of Dialysis.
Duration of
Dialysis |
number of CKD patients |
Total Vit B12 (Mean ± sd) |
Active B12
(HoloTc) (Mean ± sd) |
< 5 YEARS |
52 |
456 ± 63 |
73 ± 13 |
> 5 YEARS |
51 |
115 ± 12 |
33 ± 9 |
P value |
|
0.0001 |
0.0001 |
|
Cut Offs |
Number of CKD patients(n) |
Total Vit B12 |
lower cut off (<148pg/ml) |
7 |
higher cut off (>2000 pg/ml) |
Nil |
|
Holo TC |
lower cut off (<19 pg/ml) |
12 |
higher cut off (>128 pg/ml) |
6 |
Vitamin B deficiency is a major public health problem, particularly among older persons. Patients with CKD have high risk of developing vitamin B12 deficiency in early life and hence the cardiovascular complications associated with it. All patients with vitamin b12 deficiency will not show the symptoms of B12 deficiency. But they develop metabolic complications of B12 deficiency which will be evident in their later life. It is also possible that, in many cases, functional vit B12 deficiency is not reflected in the blood tests and it remains borderline low or within normal reference range [7]. Active B12 (Holo-TC) is important marker which can override the clinical dilemma associated with total vit B12 deficiency. It helps in early detection of vit B12 deficiency due to its faster cellular uptake and short half-life period as compared to total vit B12 [8]. In this study we compared Total B12 and Active vit B12 5 different groups of CKD patients.
Table 4: Comparison of the
validity tests of Total b12 and Holo TC in the diagnosis of functional vitamin
b12 deficiency.
Validity tests |
Vit B12 |
HoloTC |
Sensitivity |
76.4% |
85.4% |
Specificity |
62% |
72% |
Positive predictive value |
79% |
88% |
Negative predictive value |
42% |
56% |
Active B12 has better diagnostic accuracy than vitamin
b12 especially in CKD patients. Thus Active B12 (Holo TC) should be considered
for diagnosing and treating B12 deficiency in CKD patients in order to reduce
the risk of cardiovascular morbidity and mortality in these patients.