Recently, in one of the blogs, I discussed NGAL. In that
blog, I mentioned cystatin C (CC). It
occurred to me that all laboratories do not offer CC. Here, adapted from the
September, 2013 issue of Am. J. of Kidney Disease, is a series of questions and
answers about cystatin.
What if my lab cannot
measure cystatin C?
The 2012 KDIGO guidelines will likely increase demand for CC, and we
encourage clinicians to request CC from their clinical labs.
Is CC too expensive
for routine measurement?
Because CC is automated, the labor costs are minimal and the primary costs
are the reagents. This cost is less than or equivalent to the cost of several
tests that nephrologists and cardiologists frequently order: troponin (~ $10),
and B-type natriuretic peptide (~$15).
Which equation should
The new CKD-EPI equations currently appear to be the best available GFR
estimating equations using CC.
The choice of the combined creatinine-CC equation versus the
CC alone equation depends upon the diagnostic strategy. If the goal is to
choose the optimal GFR estimate for either screening or a specific clinical
indication, then the combined eGFR(cr-cys) should be used. On the other hand,
if CC is used as a secondary test based on the results of eGFRcr, then the
eGFRcys should be used so that creatinine is not in both the screening and
verification steps of a GFR estimating strategy. The approach in Sweden is to
compare the eGFRcr and eGFRcys: if they are within 40% of one another, then
their average is the best estimate; if the difference is >40%, then
clinicians should choose the estimate least likely to be biased based on
Is it important to
monitor changes in eGFR using CC?
Cystatin C may have advantages over
creatinine for detecting acute changes in eGFR in the hospital setting for
patients in intensive care; however, minimal difference was observed for
patients undergoing cardiac surgery.50,51 Overall, we do not believe that
routine use of cystatin C is warranted for monitoring acute changes in kidney
1. Am J
Kidney Dis. Sep 2013; 62(3): 595–603. This review article is available free. Just
click on the reference itself.
Recently, near my home in Texas, there was an Ebola scare
when a case appeared quite unexpected until a little investigation discovered
that the patient had been exposed on a recent trip. This suggested to me that a
short blog on Ebola was in order. Ergo…
As of August 13, 2014, 2,127 patients across four West
African countries have been infected with the Ebola virus over the past nine
months. Among these patients, approximately 50 percent subsequently died from the
disease. Ebola is transmitted only by patients who already present symptoms of
the disease, and infection only occurs upon only direct contact with the blood
or body fluids of an Ebola patient. Consequently, transmission of the outbreak
can be contained through careful monitoring for fever among persons who have
visited, or come into contact with persons from, the site of the outbreak.
Thus, patients suspected of presenting symptoms characteristic of Ebola should
Here is where we are with regard to vaccines:
EBOV vaccine candidates have been identified in preclinical studies
EBOV vaccines are immunogenic in human clinical trials
• An ideal
EBOV vaccine will give rapid and durable immunity against multiple EBOV species
Medicine 2014, 12:196
2. Neth J
Med. 2014 Nov;72(9):442-8.
3. J Venom
Anim Toxins Incl Trop Dis. 2014 Oct 3;20(1):44
4. BMC Med.
2014 Oct 10;12(1):196
Atypical squamous cells of undetermined significance (ASCUS)
and low-grade squamous intra-epithelial lesions (LSIL) are minor lesions of the
cervical epithelium detectable by cytological examination of cells collected
from the surface of the cervix of a woman. Usually, women with ASCUS and LSIL
do not have cervical (pre-) cancer. However, a substantial proportion of them do
have underlying high-grade cervical intra-epithelial neoplasia (CIN, grade 2 or
3) and are at increased risk for developing cervical cancer. Therefore,
accurate triage of women with ASCUS or LSIL is required to identify those who
need further management.
Arbyn et al. studied two approaches to triage women with
ASCUS or LSIL: 1) Repeating the cytological test, and 2) DNA testing for high-risk
types of the human papillomavirus (hrHPV) -- the main causal factor of cervical
cancer. They concluded that HPV-triage with HC2 for assay can be recommended
because it has higher accuracy (significantly higher sensitivity, and similar
specificity) than repeat cytology. When triaging women with LSIL, an HC2 test
yields a significantly higher sensitivity, but a significantly lower
specificity compared to a repeat cytology. Therefore, practice recommendations
for management of women with LSIL should be balanced, taking local
circumstances into account. (Keep in mind that it is possible that, by lowering
the sensitivity, the specificity will increase, and thus it is possible that HC2
and cytology may be quite similar.)
It is the practice in some places that repeat cytology and
HPV testing comprise delayed triage. Sorbye et al. compared HPV mRNA with HPV
DNA to determine which was better for the HPV part. Their follow-up study of
311 women aged 25-69 years with ASC-US/LSIL index cytology indicated that, in triage of repeated ASC-US/LSIL, HPV mRNA testing is more specific and is
more relevant in clinical use than an HPV DNA test.
Database Syst Rev. 2013 Mar 28;3:CD008054. HPV testing versus repeat
2. PLoS One.
2014 Nov 18;9(11):e112934. HPV mRNA Is More Specific than HPV DNA
Pharm Des. 2013; 19(8):1401-5. HPV mRNA testing in triage of women with ASC-US
cytology may reduce the time for CIN2+diagnosis compared with repeat cytology.
During the past few years a number of investigations of NGAL have demonstrated that this marker is a "useful biomarker in clinical nephrology which is helpful to diagnosis and evaluate the categories for CKD proposed by the KDIGO." In a recent study Xiang et al found that the concentration of the NGAL increased progressively with the increasing of risk categories (proposed by the revised CKD classification). The cutoff value of NGAL was calculated from stage 2 to stage 5. ROC analysis showed the AUC (serum NGAL > 0.8, urine NGAL > 0.7) and high specificity (sNGAL > 87%, uNGAL > 90%) on the cutoff value of NGAL. Along the same lines, Shen et al noted five positive results in their study of NGAL: First, the serum NGAL levels of patients with stage 2-4 CKD were significantly increased compared with the control group. Second, there were positive correlations between NGAL and cystatin C levels and between NGAL and serum creatinine levels. Third, bounded by the progress of renal function, the area under the curve of serum NGAL was 0.87. A cut-off level of 246 ng/mL gave a sensitivity of 85% and a specificity of 82%. Fourth, Kaplan-Meier survival curve analysis showed that the serum NGAL level was closely related to the end-point of renal function in patients with CKD. Fifth, Cox multivariate regression analysis showed that the estimated glomerular filtration rate and blood NGAL are associated with progression of CKD.
1. Int J Clin Exp Pathol. 2014 Sep 15;7(10):7172-81
2. Nephrology (Carlton). 2014 Mar;19(3):129-35
3. Am J Kidney Dis. 2009 Dec;54(6):1012-24
Pre-analytical errors remain the most common source of
errors that a hospital laboratory must deal with. Specimen rejection is one of
the pre-analytical errors. These while rare (0.2% Ref. 1), they have
significant results – patient discomfort, delays in correct sample and a high
rate of specimen or test discarded.
In a recent study Karcher and Lehman (1) found that the
reason for most rejected specimens (92.4%) was inappropriate or inadequate
specimen. The remaining 7.6% were rejected owing to improper labeling.
Regarding specimens found to be improperly labeled, most (73.6%) were detected
by laboratory review (“lab check”), 9.9% by feedback from caregiver, and 9.1%
by delta check during the analytical phase.. Most rejected specimens (87.7%)
were ultimately recollected, 1.1% were relabeled or corrected, and 11.2% were
abandoned (neither recollected nor relabeled .)
Specimen rejection led to a (1) high rate of specimen
recollection, (2) delay in result availability (median of 65 minutes), and (3)
high rate of specimen/test abandonment. Relabeling of incorrectly labeled
specimens was found to be of little benefit and was associated with a
substantial percentage of subsequently mislabeled specimens.
Hemolyzed specimens continue to be a frequent occurrence in
clinical laboratories. The prevalence can be as high as 3.3% of all of the
routine samples, accounting for up to 40%-70% of all unsuitable specimens
identified, nearly five times higher than other causes, such as insufficient,
incorrect and clotted samples.
Pathol Lab Med. 2014 Aug;138(8):1003-8.
2. Clin Chem
Lab Med. 2008;46(6):764-72
I have seen data recently that indicate that some
laboratories are not using their measured SDs (and sometimes means) for
monitoring their QC. This can have two ramifications:
1) the QC will appear to be in control more often, saving
time and trouble and
2) the analytical system may develop an error that could be
missed by the incorrect SD (and mean).
This would lead to erroneous data being reported to the
clinical staff. Which could lead to a missed diagnosis, an incorrect diagnosis,
more laboratory tests, perhaps ‘scans’ or biopsies or worse. This is especially
possible if the QC system does not use both the TE (total error = bias + 2*SD)
AND the total error allowed (TEa, from for example CLIA or CAP) as a limit. In
other words the TE must be less than the TEa for the QC system to be in
Here is an example of what I am saying. Suppose the SD for
an analyte is 3.0 with a mean of 52 (and a peer mean of 50) and a TEa of 18%. The
%TE is (52-50)*100/50 +2*6% =16%. Which is within the TEa. Suppose, however the
laboratory sets the SD at 5. Without looking into the TEa the laboratory may go
along reporting errors without being aware of that. It is obvious that setting
the SD incorrectly is less likely if both TE and TEa are used to set the QC
system. Using both will also help choose the best QC rule(s). Please use the
measured mean and SD from YOUR QC data and check them when changing reagents
and/or calibrators and choose QC rules based on both TE and TEa.
calibrators and choose QC rules based on both TE and TEa.
Upon emerging from the thymus, naive T cells circulate in
the blood through lymph nodes and seek foreign (“nonself”) antigens. T cells
can recognize not only pathogen-associated antigens, but also abnormally
expressed self-proteins—indicating mutated or transformed tumorigenic cells -- as
“nonself.” If T cells encounter their specific antigen in the context of
appropriate co-stimulatory molecules, the cells become activated and upregulate
activation and homing molecules. These T cells, termed effector T cells, are
able to enter inflamed tissues in search of infected or cancerous cells. Among
other functions, effector T cells can produce inflammatory cytokines and/or
cytolytic granules, leading to apoptosis or necrosis of infected or tumor
cells. The use of immunotherapy to unlock the immune system’s ability to
eradicate cancer cells is an exciting new avenue for treatment of solid tumors
-- even in an extremely aggressive disease with poor prognosis, such as
advanced lung cancer -- but the exact clinical applications are still not
In lung cancer therapy, the emergence of targeted agents
with mechanisms of action based on driver mutations have introduced a set of
standard predictive biomarkers to aid in clinical decision making. Immune
checkpoint blockade, however, is designed to act on a complex and intact
immunological pathway rather than individual mutations or antigens. As such,
identification of a predictive biomarker has proven challenging. Answers as to
whether biomarkers such as PD-L1 can predict tumor responsiveness to agents
targeting this pathway have been equivocal so far.
In summary, the goal of immunotherapy is to prolong survival
and quality of life for patients with lung cancer by stimulating the patient’s
own immune system to combat cancer. This new treatment approach is still earl
and more data from mechanistic and clinical studies are needed on strategies to
optimize the clinical impact of these therapies.
1. Clinical Pharmacology & Therapeutics (2014); 96 2,
4. Groopman, J, The T-cell Army, The New Yorker, April 23,
In mid-2013, William Kuhens was diagnosed with myelogenous
leukemia (AML). The only treatment for him was experimental. He was assigned in
a Phase 1 trial with little hope -- for these studies are usually used only to investigate
what dose could be handled and what the side effects were, not to send the
cancer into remission. There were 10 patients in this trial of a new drug,
AG-221, which targeted a mutated gene that affected an enzyme – isocitrate
dehydrogenase (IDH-2). Of these first 10 subjects, three died from AML before
the drug could even be evaluated, but the data on six of the remaining seven
was striking – five went into complete remission and one was in partial
remission. Nothing like that was even imagined. As of the middle of September,
Kuhens is in remission. The only side effect is that he can no long eat
mayonnaise – it doesn’t taste good. In June this year, another study of 35
other patients was reported. Fourteen patients improved – nine went into
complete remission; 10 died before the drug could begin to work.
An interesting aspect of this drug -- and another like it,
AG-120 -- is that rather than destroy the cancer cells, these two turn the
cancerous cells around so that, rather than stay immature, and given only to
reproducing and continue to mature and act ‘normal.’ Only about 25 percent of AML
patients have the mutated gene and thus are not candidates for these drugs, but
the function of the mutant genes will lead to looking for similar defects which
may be targets for similar treatment -- a new avenue to try.
A, Araujo Cruz MM, Jyotsana N, et al. Mutant IDH1 promotes leukemogenesis in
vivo and can be specifically targeted in human AML. Blood2013;122(16):2877-2887
2. Yan H,
Parsons DW, Jin G, et al. IDH1 and IDH2 mutations in gliomas. N Engl J
3. Abbas S,
Lugthart S, Kavelaars FG, et al. Acquired mutations in the genes encoding IDH1
and IDH2 both are recurrent aberrations in acute myeloid leukemia: prevalence
and prognostic value. Blood 2010;116(12):2122-2126. FREE Full Text
There was a point-counterpoint “debate” in a recent issue of
Clinical Lab News. Arguing for reporting A1c as SI was Ian Young from Ireland;
for keeping A1c as percentage -- at least in the United States -- was David
Sacks from the NIH in Bethesda, MD.
Young posited that the use of percent gave values that were
quite similar to the SI units (mmol/L) for glucose and are confusing to both
patients and physicians. He pushed for using SI units for A1c. We will assume
that the total hemoglobin A would remain in SI as it now is. Thus, it seems
that two values would be necessary for A1c – the A1c and Hgb A. Although this was
not mentioned by Dr. Young, to me, this would not be an answer for it is the
relative amount of A1c that is of interest – not the absolute amount. IF only
the amount of A1c were reported (without the Hgb A), how would a patient of a
physician know whether that individual was in glucose control? I am certain
that physicians can explain the A1c as a percent to a patient who can remember
that 6 percent is good and 6.5 is not so good. And there are the H and L and “interpretative
comments” to help the patient if the clinician does not explain it. I vote for
percent around the world.
I recently read that the journal Science sent out an article under a pseudonym and an imaginary
address to several hundred journals asking that the article be published. The
article had not basis in fact and had a few patently false statements.
Curiously(?), nearly half of the journals accepted the article. Science withdrew the article from those
who accepted it. One must wonder how often such articles, often unwittingly,
are submitted and printed.
We all know that hemoglobin A1c (A1c) is a good marker for
the amount of glucose in the blood stream and that a level of 6.0 percent is
considered “normal.” As Oscar Wilde had
one of his characters in the Importance of Being Earnest say, “Life is rarely
pure and never simple.” I am sure we
would all agree with this. There was an
article in the July issue of the Mayo Clinic Proceedings that discussed a group
of 1141 ‘non-diabetic’ patients who underwent coronary angiography. The
patients were divided into four subgroups based on their A1c levels (<5.5%,
5.5-5.7%, 5.8-6.1% and >6.1%). The
study found that patients with higher A1c levels “tended to be older, over
weight and hypertensive.” They also had
higher blood glucose levels and low GFR rates. The study concluded that “the A1c level has a linear incremental
association with CAD in non-diabetic individuals. The A1c level is also
independently correlated with disease severity and higher SYNTAX scores (an
angiographic grading tool to determine the complexity of coronary artery
disease). Thus, A1c measurement could be used to improve cardiovascular risk
assessment in non-diabetic individuals.” This seems to cast some doubt about whether a 6 percent level of A1c is
A1c in non-diabetic patients: an independent predictor of coronary artery
disease and its severity. Mayo Clin Proc. 2014 Jul;89(7):908-16. Garg N, Moorthy N, Kapoor A,
of glycemic variability and glycated hemoglobin as risk factors of coronary
artery disease in patients with undiagnosed diabetes. Chin MedJ (Engl). 2012
Jan;125(1):38-43. 1, Su G, Li Z, et al.
intolerance, as reflected by hemoglobin A1c level, is associated with the
incidence and severity of transplant coronary arteryMi SH disease.[J Am Coll
Cardiol. 2004] J Am Coll Cardiol. 2004 Mar 17;43(6):1034-4 Kato T, Chan MC, Gao
SZ, et al.
In 1974, the College of American Pathologists (CAP) proposed
an algorithm for accepting/rejecting analytical runs using 2 controls. The algorithm used 3 rules to reject a run –
1 3SD,* 2 2SDw and 2 2SDa. In 1981,
Westgard et al. (JOW) proposed an expanded set of rules. Both groups were clear on the idea that a
single value beyond the 2 SD limits was not a reject signal.
In the past 40 years, improvements in instruments, reagents
and calibrators have resulted in a significant improvement of precision. This improvement suggests that QC monitoring
systems should review rules based on the SDs from current data, not based on
data from 30-plus years ago. Do we use 30 year old instruments? Or computers? Or phones?
At the AACC meeting in July, 2014, I presented a poster
looking at the changes in precision since 1988. Surveys from 1988 and 2012 were
studied. We used %CV to correct for the
variation in means from one survey to another. Our survey of 35 analytes from
chemistry, hematology and hemostasis indicated a decrease of 40 percent (average;
range 24-77) in CVs.
The table shows representative changes in SDs measured as
%CV and the change over time.
1988 2012 %Change
Analyte Method Mean %CV Mean %CV
Hemoglobin Coulter 2.9 1.7 41
WBC Coulter 3.8 2.7 24
Cholesterol Abbott 2.9 1.0 66
AST Roche 8.4 5.2 33
Ca Baker 4.9 1.3 77
Prothrombin time * 6.4 2.8 56
APTT Stago 10.4 2.9 78
*In 1988 most laboratories user a manual method.
changes in analytical precision strongly suggest that QC rules be reevaluated.
We "translated" the SD of the year 2012
into a new set of rules to detect both systematic and increased random
errors. Our translations indicate that
based on a 40 percent decrease the following rules would work very effectively: 1 4 SD, 2 3 SD, and R 5 SD. If you are squeamish about the 1 4 SD rule, use either 1 3 SD or at least 1 2.5 SD
changes in the rules will yield essentially 0% false rejects and an error
detection of nearly 100%
• As before
each analyte should be assessed to determine the proper rule(s).
I ran across an article recently that I thought you, like
me, would find it interesting. The title of the article is “Effect of
non-alcoholic beer on Subjective Sleep
in university stressed
population.” Of course, you easily relate
to the word “stressed.” Who working in a
laboratory isn’t stressed? The other
part of the title was the idea of “non-alcoholic beer.” You may, as did I, say how can that be? What is beer if not alcoholic? But is does exist – if only to get the hops
into your system. It turns out that beer
is the only beverage that contains hops, and hops is known to have a sedative
Here is the result of this study and another one carried out
on nurses. There is a sleep quality
index from Pittsburgh that measures the quality of your sleep and uses the 30
students as their own control for the first week of three. During the last two weeks, the students were
asked to drink the NAB at dinner and then fill out the survey. The overall rating improved significantly
(“p<0.05”), as was the sleep latency also a level of significance of
“<0.05.” As I mentioned, another study measured other aspects of sleep and
found the same high level of significance.
It turns out that there are quite a number of non-alcoholic
beers, although they can contain as much as 1.0% (but usually 0.5%) alcohol.
1. Acta Physiol Hung. 2014 Sep;101(3):353-61..Effect of
non-alcoholic beer on Subjective Sleep Quality in a university stressed
population. Franco L, Bravo R, Galán C, et al.
2. PLoS One. 2012;7(7):e37290. The sedative effect of
non-alcoholic beer in healthy female nurses. Franco L Sánchez C, Bravo R, et al.
I have been working with troponin since it came to this country several years ago. Most of my experience has been with troponin I (cTnI). When cTnI first was released to the laboratories the cut-off was set at 0.4. Then it dropped to 0.2 and now it has been lowered by some laboratories even further. These newer variations have pros and cons as you have seen. For example, there are reports of measurable cTn following a marathon.
"The increase in early diagnostic sensitivity of hs-cTn assays for ACS comes at the cost of a reduced ACS specificity, because more patients with other causes of acute or chronic myocardial injury without overt myocardial ischemia are detected than with previous cTn assays."
These newer assays detect low levels of cTn in apparently healthy people. "In addition, the sensitive assays detect more cTn positive patients who do not have a final diagnosis of ACS. It is unknown if such mild elevations in cTn detected by sensitive assays are of clinical concern. What is certain is that AMI remains a clinical not a biochemical diagnosis and interpretation of cTn concentrations should be made according to the clinical context." It has been demonstrated that the newer assays are better able (using the area under the ROC curve) to identify AMI in patients with existing CAD compared to the ‘standard' cTn.
A diagnostic accuracy study of patients presenting to the emergency department (ED) with symptoms of ACS was performed. Troponin was measured at 0, 2 and 6h post-presentation. AMI was made by 2 cardiologists and incorporated the 0 and 6h troponin values measured by a sensitive troponin assay. There was no significant difference in the diagnostic accuracy of early versus late biomarker strategies when used with the current risk stratification processes. Incorporation of a significant delta did not improve the stratification at 2h post-presentation."
1. Mair J., World J Cardiol. 2014 Apr 26;6(4):175-82.
2. Gaze DC., Curr Med Chem. 2011;18(23):3442-5. Curr Med Chem. 2011;18(23):3442-5.
3. Reiter M, Twerenbold R, Reichlin T, et al. Eur Heart J. 2012 Apr;33(8):988-97.
4. Cullen L, Greenslade J, Than M et al., Heart Lung Circ. 2014 May;23(5):428-34.
Laboratories have a major impact on patient safety: 80-90% of all the diagnoses are made on the basis of laboratory tests. Laboratory errors have a reported frequency of 0.012-0.6% of all test results.
Patient safety is a managerial issue which can be enhanced by implementing active system to identify and monitor quality failures. This can be facilitated by reactive method which includes incident reporting followed by root cause analysis. This leads to identification and correction of weaknesses in policies and procedures in the system. Another way is a proactive method like Failure Mode and Effect Analysis.
Here are synopses of two studies aimed at quantifying preanalytical errors which can be reduced by continuous education and FMEA approaches. In a study of data from 105 laboratories and 4,715,132 tubes during the data collection period, according to determinations by clinicians in the request form, 32,977 (0.7%) were found to be rejected. Whole blood-EDTA samples and serum samples accounted for 76% of all samples collected among laboratories, although they corresponded to only 56% of all rejections. In total, 81% of rejections arose as a result of the following reasons:
- "specimen not received" (38%),
- "hemolysis" (29%), and
- "clotted sample" (14%).
Moreover, plasma-citrate-erythrocyte sedimentation rate exhibited the highest percentage of rejection (1.5%), whereas the lowest rate corresponded to whole blood-EDTA (0.38%).
During a 1-year period, a total of 168,728 samples and 88,655 requests forms were received in a Stat laboratory. The total number of preanalytical errors was 1457, accounting for 0.8% of the total number of samples received in a year. Of the total preanalytical errors, 46% were hemolysed samples (biochemistry), 43% were clotted samples (hematology), 6% were samples lost-not received in the laboratory, 2.9% samples showed an inadequate sample-anticoagulant ratio, 0.7% were requests with errors in patient identification, 0.3% were samples collected in blood collection tubes with inappropriate anticoagulant and 0.1% were requests with errors -- missing test requests.
- Alsina MJ, Alvarez V, Barba N, et al. Clin Chem Lab Med. 2008;46(6):849-54.
- Grecu DS, Vlad DC, Dumitrascu V. Lab Med. 2014 Winter;45(1):74-81.
- Agarwal R. Indian J Clin Biochem. 2013 Jul;28(3):227-34.
For more on Failure Mode and Effect Analysis (FMEA) see http://asq.org/learn-about-quality/process-analysis-tools/overview/fmea.html and http://www.ihi.org/resources/Pages/Tools/FailureModesandEffectsAnalysisTool.aspx
Why can humans (and guinea pigs and dry-nosed primates and bats) not make vitamin C and are thus open to scurvy without replacement?
Many years ago, I worked on a study of guinea pigs that had been fed a diet without vitamin C and thus developed scurvy. I knew that people, like the guinea pigs, could develop scurvy without adding the vitamin to our diet. This has been known for more than a century and in the last few years we have found out why it happens to these few animals.
The inability of humans to synthesize L-ascorbic acid is known to be due to a lack of an enzyme that is required for the biosynthesis of this vitamin. The enzyme is known as L-gulono-gamma-lactone oxidase (GULO). Isolation of a cDNA for the rat enzyme resulted in a study of the basic defect underlying this deficiency at the gene level and led to isolation of a human genomic clone related to L-gulono-gamma-lactone oxidase as well as three overlapping clones covering the entire coding region of the rat L-gulono-gamma-lactone oxidase cDNA. Sequence analysis study indicated that the human L-gulono-gamma-lactone oxidase gene has accumulated a large number of mutations since it stopped being active and that it now exists as a pseudogene in the human genome.
This genetic defect has not been selected against in natural selection as we are able to consume more than enough vitamin C from our diet. It is also suggested that organisms without a functional GULO gene have a method of "recycling" the vitamin C that they obtain from their diets using red blood cells.
- Cell. 2008 Mar 21;132(6):1039-48
- Hum Gene Ther. 2008 Dec;19(12):1349-58
- Am J Clin Nutr. 1991 Dec;54(6 Suppl):1203S-1208S.