Blog entry by Meguid El Nahas
READ BLOG AFTER ABSTRACT:
Article by Peraza et al published in the April 2012 issue of AJKD.
BACKGROUNd; An epidemic of chronic kidney disease of unknown cause has emerged along the Pacific coast of Central America, particularly in relatively young male sugarcane workers. In El Salvador, we examined residence and occupations at different altitudes as surrogate risk factors for heat stress.
STUDY DESIGN: Cross-sectional population-based survey.
SETTING & PARTICIPANTS:
Populations aged 20-60 years of 5 communities in El Salvador, 256 men and 408 women (participation, 73%): 2 coastal communities with current sugarcane and past cotton production and 3 communities above 500 m with sugarcane, coffee, and service-oriented economies.
Participant sex, age, residence, occupation, agricultural history by crop and altitude, and traditional risk factors for CKD.
Serum creatinine (SCr) level greater than the normal laboratory range for sex, estimated glomerular filtration rate (eGFR) <60 mL/min/1.73 m(2), and proteinuria categorized as low (protein excretion ≥30-<300 mg/dL) and high grade (≥300 mg/dL).
Of the men in the coastal communities, 30% had elevated SCr levels and 18% had eGFR <60 mL/min/1.73 m(2) compared with 4% and 1%, respectively, in the communities above 500 m. For agricultural workers, prevalences of elevated SCr levels and eGFR <60 mL/min/1.73 m(2) were highest for coastal sugarcane and cotton plantation workers, but were not increased in sugarcane workers at 500 m or subsistence farmers. Women followed a weaker but similar pattern. Proteinuria was infrequent, of low grade, and not different among communities, occupations, or sexes. The adjusted ORs of decreased kidney function for 10-year increments of coastal sugarcane or cotton plantation work were 3.1 (95% CI, 2.0-5.0) in men and 2.3 (95% CI, 1.4-3.7) in women.
The cross-sectional nature of the study limits etiologic interpretations.
Agricultural work on lowland sugarcane and cotton plantations was associated with decreased kidney function in men and women, possibly related to strenuous work in hot environments with repeated volume depletion.
ANOTHER INTERPRETATION OF THIS STUDY COULD BE:
Dehydration in Agricultural workers working in extreme heat. Whilst the naive cover of the April issue of AJKD falls for it and suggests and "EPIDEMIC"of kidney disease in Central America...the critical reader would notice:
1. Cross sectional analysis with a SINGLE serum creatinine measurement does NOT identify an "EPIDEMIC" of kidney disease!!!!
2. CKD takes more than a single measurement of serum creatinine.
3. Raised serum creatinine in heat exposed manual workers is more likely to reflect dehydration under extremely strenuous conditions.
4. The control group working in the same agricultural fields, sugarcane and cotton plantation, but in the cooler altitude areas of El salvador dont seem to suffer as much...Heat and dehydration being less prevalent in cooler higher altitude!
5. Women in hot coastal areas dont seem to share the men heat induced raised creatinine risk because they have a smaller muscle mass and their serum creatinine is lower; MDRD calcuklated GFR does not fully correct for difference in body mass. I also suspect that women are assigned less strenuous agricultural role with less exposure to heat.
Once more nephrologists have forgotten:
1. That serum creatinine can be raised for many reasons including:
High meat diet, high muscle mass and dehydration; all potential confounders in hard working male agricultural workers.
2. That raised serum creatinine in a cross sectional study doesnt make for CKD!
3. That raised serum creatinine measured once does not make for an EPIDEMIC...!!!
WHEN WILL NEPHROLOGISTS LEARN???